Showing 1–50 of 568 results for author: Smail, I

A redshift of z=3.20 for the bright arc in eMACSJ2229.9-0808: Comment on Wagner & Falco (2026) "Hamilton's Object revisited: A challenging source redshift of a strong lensing configuration"

Authors: Ian Smail, Johan Richard, Harald Ebeling, A. C. Edge

Abstract: We re-analyse near-infrared and optical spectroscopy from the Subaru, Gemini, and Keck telescopes of the bright gravitational arc seen in the z=0.62 X-ray cluster eMACSJ2229.9-0808. The 22 strongest spectral features we identify uniquely determine the redshift of the galaxy as z=3.20, as previously reported by Ebeling et al. (2025), not z=0.82 as claimed by Wagner & Falco (2026). We re-analyse near-infrared and optical spectroscopy from the Subaru, Gemini, and Keck telescopes of the bright gravitational arc seen in the z=0.62 X-ray cluster eMACSJ2229.9-0808. The 22 strongest spectral features we identify uniquely determine the redshift of the galaxy as z=3.20, as previously reported by Ebeling et al. (2025), not z=0.82 as claimed by Wagner & Falco (2026). △ Less

Submitted 7 July, 2026; originally announced July 2026.

Comments: Comment article in A&A, in press. Refers to arXiv:2604.19867

Investigating the role of turbulence in the interstellar medium in $z\sim3$ dusty star-forming galaxies using kpc-resolution ALMA dust and gas maps

Authors: B. A. Westoby, J. A. Hodge, P. Sharda, P. E. Mancera Piña, M. Rybak, E. da Cunha, J. Li, I. Smail, A. M. Swinbank, A. Battisti, L. A. Boogaard, W. N. Brandt, G. Calistro Rivera, C. -C. Chen, P. Cox, M. Cracraft, H. Dannerbauer, R. Decarli, T. R. Greve, S. Kendrew, K. Knudsen, C. -L. Liao, J. van Marrewijk, O. Nayak, M. Neeleman , et al. (6 additional authors not shown)

Abstract: We present ALMA high-resolution ($\sim$0.25$^{\prime\prime}$/2 kpc) CO(5-4) and CO(4-3) observations of three $z\sim 3$ submillimetre-selected dusty galaxies from the ALESS survey. These data complement existing [sub]-kpc scale ALMA 870$μ$m continuum imaging and JWST NIRCam and MIRI imaging from the ALESS-JWST program, allowing us to trace the molecular gas, dust-obscured star formation, and stell… ▽ More We present ALMA high-resolution ($\sim$0.25$^{\prime\prime}$/2 kpc) CO(5-4) and CO(4-3) observations of three $z\sim 3$ submillimetre-selected dusty galaxies from the ALESS survey. These data complement existing [sub]-kpc scale ALMA 870$μ$m continuum imaging and JWST NIRCam and MIRI imaging from the ALESS-JWST program, allowing us to trace the molecular gas, dust-obscured star formation, and stellar populations on similar spatial scales. We spectroscopically confirm that two of the sources lie at the same redshift and are likely interacting. We find that the molecular-gas distribution broadly follows the dusty star-forming structures seen in the 870$μ$m dust continuum imaging, but that the gas reservoirs are significantly more extended than the dust emission with a spatial extent comparable to the rest-frame near-infrared stellar emission. By modeling the kinematics for the two highest signal-to-noise sources, we find that the galaxies are well-fit by rotating disc models with high ratios of ordered to random motion ($V_{\rm{max}}/\overlineσ=5\pm1$ and $6\pm1$), although smaller-scale kinematic deviations cannot be ruled out at the current sensitivity and spatial resolution. Finally, utilizing the high-resolution 870$μ$m dust continuum and CO data, we investigate star-formation scaling relations on kpc-scales in these high-redshift galaxies. Assuming a constant CO-to-H$_{2}$ conversion factor and excitation ratio, we find that the data are offset from theoretical star-formation relation predictions that do not take turbulence into account, but consistent with gravo-turbulent models, thereby suggesting that turbulence plays a central role in regulating star formation at high redshift. △ Less

Submitted 9 June, 2026; originally announced June 2026.

Journal ref: Mon Not R Astron Soc (2026)

Extending the ALMA survey of the SCUBA-2 CLS UDS field: Tracing the obscured formation of spheroids across z~1-4

Authors: Ian Smail, Steven Gillman, Ugne Dudzeviciute, A. M. Swinbank

Abstract: We investigate the properties of 870-um selected galaxies at z~1-4 with FIR luminosities of LIR~1e11-1e13Lo, encompassing systems that dominate obscured activity at the peak of cosmic star formation, to identify variations in star-formation processes as a function of dust mass and redshift. We revisit ALMA 870-um continuum maps from the ALMA/SCUBA-2 UDS (AS2UDS) survey, lowering the source selecti… ▽ More We investigate the properties of 870-um selected galaxies at z~1-4 with FIR luminosities of LIR~1e11-1e13Lo, encompassing systems that dominate obscured activity at the peak of cosmic star formation, to identify variations in star-formation processes as a function of dust mass and redshift. We revisit ALMA 870-um continuum maps from the ALMA/SCUBA-2 UDS (AS2UDS) survey, lowering the source selection threshold from 4.3 sigma to 3.1 sigma to enlarge the sample with S870~1mJy. To reduce contamination from noise peaks, we match submm sources to a K-selected galaxy sample and apply cuts on photometric redshift and near-infrared (H-K) colour. This yields 84 sources in our extended AS2UDS survey, AS2UDSx, with S870=0.3-2.2mJy, doubling the sample at S870~1mJy relative to the original study. Using this expanded sample, we find that submm galaxies with S870~1mJy at z>~2.5 share properties with brighter, more active populations, while those at z<~2.5 are distinct, with lower gas fractions, shorter depletion times, and stellar morphologies from JWST imaging that show less structured dust obscuration, resembling less-active field galaxies. This indicates a shift in the characteristics of 870-um-selected galaxies at S870~1mJy and z~2, likely driven by the stability of their gas discs. Brighter and higher-z galaxies can sustain dense, globally unstable discs through efficient gas accretion, powering compact obscured starbursts. In contrast, fainter systems at z<~2.5 lack this accretion, leading to more stable discs and more extended dust continuum emission. This suggests a natural division around S870~1mJy and z~2: lower-z, fainter sources represent the most active secularly-driven extended star-forming discs, while similar and brighter, higher-z submm galaxies form a distinct population of compact starbursts within massive, unstable, gas-rich discs, consistent with progenitors of massive spheroids. △ Less

Submitted 20 April, 2026; originally announced April 2026.

Comments: Submitted to MNRAS, comments welcome

Journal ref: Mon Not R Astron Soc (2026)

ALESS--JWST: Dust-driven Morphologies and Hidden Stellar Mass in $z\sim3$ Sub-millimeter Galaxies

Authors: J. Li, E. da Cunha, J. A. Hodge, I. Smail, S. Kendrew, A. battisti, M. Cracraft, L. A. Boogaard, W. N. Brandt, C. -C. Chen, P. Cox, K. K. Knudsen, C. -L. Liao, G. Calistro Rivera, M. Rybak, A. M. Swinbank, P. van der Werf, F. Walter, A. Weiss, B. A. Westoby

Abstract: We present JWST/NIRCam and MIRI observations of twelve $z\sim3$ sub-millimeter galaxies (SMGs) from the ALESS survey, combined with high-resolution ($0.08''-0.16''$) ALMA 870$μ$m imaging, enabling spatially resolved SED fitting on $\sim$kpc scales. We find a resolved star-forming main sequence linking surface densities of star formation rate and stellar mass, suggesting star formation remains tigh… ▽ More We present JWST/NIRCam and MIRI observations of twelve $z\sim3$ sub-millimeter galaxies (SMGs) from the ALESS survey, combined with high-resolution ($0.08''-0.16''$) ALMA 870$μ$m imaging, enabling spatially resolved SED fitting on $\sim$kpc scales. We find a resolved star-forming main sequence linking surface densities of star formation rate and stellar mass, suggesting star formation remains tightly coupled to local mass distribution even in obscured systems. Our resolved SED analysis reveals a systematic stellar mass bias in integrated fits, even including rest-frame $\sim2μ$m MIRI imaging. Rather than classical `outshining', this is mainly driven by spatially varying dust attenuation, indicating a `dust-obscuration bias' that causes obscured stellar mass to be missed. We show SMG morphologies are wavelength-dependent. At rest-frame optical wavelengths, central obscuration produces stellar-dust offsets and inflated sizes, while at longer wavelengths these effects diminish. The rest-frame $\sim1.5-3μ$m MIRI imaging is less affected by dust than NIRCam and reveals compact stellar structures matching the 870$μ$m dust continuum. We find centrally concentrated dust attenuation drives both offsets and size variations, demonstrating dust geometry is the main driver of structural diversity. Consequently, morphologies from rest-frame wavelengths $\lesssim1.6μ$m can be biased without longer-wavelength constraints. The intrinsic stellar mass and dust continuum sizes are consistent ($R_\mathrm{e,870μm}/R_\mathrm{e,\ast}=1.0\pm0.4$), supporting a picture in which SMGs host compact, obscured star formation that builds dense stellar cores, consistent with evolution into massive quiescent galaxies. We suggest such obscured structures and associated biases may also be common among massive star-forming galaxies at $z\gtrsim1$, implying these effects are likely of broad relevance. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: Submitted to Astrophysical Journal

JWST's PEARLS: A clumpy ring galaxy at $z = 4.0148$

Authors: David Vizgan, Ming-Yang Zhuang, Ian Smail, Rogier Windhorst, Gibson Bowling, Cheng Cheng, Seth Cohen, Christopher Conselice, Jose Diego, Brenda Frye, Norman Grogin, Rolf Jansen, Patrick Kamieneski, Anton Koekemoer, Rafael Ortiz III, Massimo Ricotti, Bangzheng Sun, Hayley Williams, S. P. Willner, Haojing Yan, Aadya Agrawal, Manuel Solimano, Zachary Stone, Joaquin Vieira, Chentao Yang

Abstract: Ring galaxies are an uncommon class of galaxies whose morphology is closely related to dynamical processes that govern galaxy evolution. Some ring galaxies, known as "collisional ring galaxies", are thought to form as a consequence of head-on collisions between galaxies, and a number of high-redshift collisional ring galaxies have been discovered and/or studied in the era of the James Webb Space T… ▽ More Ring galaxies are an uncommon class of galaxies whose morphology is closely related to dynamical processes that govern galaxy evolution. Some ring galaxies, known as "collisional ring galaxies", are thought to form as a consequence of head-on collisions between galaxies, and a number of high-redshift collisional ring galaxies have been discovered and/or studied in the era of the James Webb Space Telescope (JWST). In this paper, we present HST/ACS, JWST/NIRCam, and JWST/NIRSpec observations of a candidate ring galaxy at $z_{\rm spec} = 4.0148$, previously identified as a potential gravitational lens. The galaxy exhibits a complex morphology, including three bright clumps along an apparent ring with radius $\approx 0.25$" $\simeq 1.8$ kpc. It has a total SFR $= 140^{+20}_{-30}$ ${\rm M}_{\rm \odot}$ yr$^{-1}$ and $\log(M_\ast/{\rm M}_\odot) = 10.41^{+0.11}_{-0.13}$, making it similar to other high-redshift collisional ring galaxies. Although we argue strongly in favor of the collisional ring explanation, we cannot entirely rule out a galaxy-galaxy strong lensing explanation for the system's morphology, in which a foreground galaxy at $z \simeq 1.7$ lenses a galaxy at $z \simeq 4.0$ into an Einstein ring-like configuration; to confirm the nature of this source, we require kinematic information via high spectral resolution observations. We suggest that current and future gravitational lens surveys should consider high-redshift ring galaxies as possible but significant contaminants. △ Less

Submitted 12 May, 2026; v1 submitted 12 March, 2026; originally announced March 2026.

Comments: 14 pages, 7 figures, 2 tables. Accepted to ApJ after minor revision

KURVS: chemical properties from multiple strong line calibrations for star-forming galaxies at $z\sim1.5$

Authors: Zefeng Li, Ugnė Dudzevičiūtė, Annagrazia Puglisi, Steven Gillman, A. Mark Swinbank, Luca Cortese, Ian Smail, Karl Glazebrook, Anna F. McLeod, Dominic J. Taylor, Roland Bacon, Christopher Harrison, Edo Ibar, Juan Molina, Danail Obreschkow, Tom Theuns

Abstract: Gas-phase oxygen abundance (metallicity) properties can be constrained through emission line analyses, and are of great importance to investigate galaxy evolution histories. We present an analysis of the integrated and spatially-resolved rest-frame optical emission line properties of the ionised gas in 43 star-forming galaxies at $z\sim1.5$ in the KMOS Ultra-deep Rotational Velocity Survey (KURVS)… ▽ More Gas-phase oxygen abundance (metallicity) properties can be constrained through emission line analyses, and are of great importance to investigate galaxy evolution histories. We present an analysis of the integrated and spatially-resolved rest-frame optical emission line properties of the ionised gas in 43 star-forming galaxies at $z\sim1.5$ in the KMOS Ultra-deep Rotational Velocity Survey (KURVS). Using the [NII]$\lambda6584$/H$α$ (N$_2$), ([OII]$λ\lambda3727,9+$[OIII]$λ\lambda4959,5007$)/H$β$ (R23), and for the first time [NII]$\lambda6584$/[OII]$λ\lambda3727,9$ (N$_2$O$_2$) indicators at this redshift, we measure the gas-phase metallicities and their radial gradients. On $\sim4$-kpc scales metallicity gradients measured from N$_2$O$_2$ and those measured from N$_2$ are in good agreement when considering the spatial distributions of dust in each galaxy, as parameterised by dust attenuation radial gradients. We report a nearly flat metallicity gradient distribution typically at $z\sim1.5$, with the 50th, 16th and 84th percentiles at $0.01$, $-0.03$, and $0.05$ dex kpc$^{-1}$, respectively. The findings agree well with previous observational studies and simulations at this epoch. We ascribe the observed negative metallicity gradients to a natural result from self-regulating systems, and the positive ones to potential galactic fountains and higher merger rates. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 18 pages, 16 figures, published in MNRAS

The VLA Frontier Fields Survey: A 6GHz High-resolution Radio Survey of Abell2744

Authors: Esteban A. Orozco, Eric F. Jiménez-Andrade, Eric J. Murphy, Ian Smail, Emmanuel Momjian, Ian Heywood, Miguel Vega-Gutierrez, Christa DeCoursey

Abstract: We present 6GHz radio continuum observations of the galaxy cluster Abell 2744 ($z = 0.307$) obtained with the Karl G. Jansky Very Large Array (VLA) as part of the VLA Frontier Fields program, the goal of which is to explore the radio continuum emission from high-redshift galaxies that are magnified by foreground massive galaxy clusters. With an rms noise of $\approx 1 μ$Jy beam$^{-1}$, in the imag… ▽ More We present 6GHz radio continuum observations of the galaxy cluster Abell 2744 ($z = 0.307$) obtained with the Karl G. Jansky Very Large Array (VLA) as part of the VLA Frontier Fields program, the goal of which is to explore the radio continuum emission from high-redshift galaxies that are magnified by foreground massive galaxy clusters. With an rms noise of $\approx 1 μ$Jy beam$^{-1}$, in the image plane, and sub-arcsec angular resolution ($θ_{1/2}=0.82''$), this is the deepest and most detailed radio image of Abell 2744 ever obtained. A total of 93 sources is detected with a peak signal-to-noise ratio $\geq5$, of which 46 have optical/near-infrared (IR) counterparts with available redshift, magnification ($μ$), and stellar mass (${M}_*$) estimates. The radio sources are distributed over a redshift of 0.15 to 3.55, with a median redshift value of $z = 0.93^{+1.48}_{-0.63}$ and with a range mass from $5.5\times 10^{9} \,\rm{M}_{\odot}$ to $1.3\times 10^{11} \,\rm{M}_{\odot}$. A comparison between the radio-based star formation rates (SFRs) and those derived from ultraviolet-to-near IR data reveals that radio SFRs are typically an order of magnitude higher. This discrepancy is likely a result of strong dust obscuration affecting the UV-to-NIR tracers. We look for radio counterparts of the so-called ``Little Red Dots (LRDs)'' galaxies at $z\approx6$ seen behind Abell 2744, but find no significant detections. After stacking, we derive a 3$σ$ upper limit to the 6GHz radio luminosity of LRDs of $4.1\times 10^{39}\,\rm erg\,s^{-1}$. Finally, we present a sample of 22 moderately/strongly lensed galaxies ($μ\gtrsim 2$) in the VLA Frontier Fields survey, which provides a zoomed view of the star formation processes within main sequence galaxies at $z\approx 1-2$. △ Less

Submitted 3 June, 2026; v1 submitted 25 June, 2025; originally announced June 2025.

Comments: 25 pages, 13 figures, 7 tables. Accepted for publication in ApJ; in press

ADF22+: a declining faint end in the far-infrared luminosity function in the SSA22 protocluster at z=3.09

Authors: Shuo Huang, Hideki Umehata, Ian Smail, Kouichiro Nakanishi, Bunyo Hatsukade, Mariko Kubo, Yoichi Tamura, Tomoki Saito, Soh Ikarashi

Abstract: Protoclusters represent the densest regions of cosmic large-scale structure in the early universe and are the environment where present-day massive elliptical galaxies are assembled. Millimeter continuum emission offers a powerful probe of obscured star formation at high redshifts across various environments. In this paper, we present a deep ALMA 1.17 mm mosaic of the central 8 arcmin$^2$ (… ▽ More Protoclusters represent the densest regions of cosmic large-scale structure in the early universe and are the environment where present-day massive elliptical galaxies are assembled. Millimeter continuum emission offers a powerful probe of obscured star formation at high redshifts across various environments. In this paper, we present a deep ALMA 1.17 mm mosaic of the central 8 arcmin$^2$ ($\approx30$ comoving Mpc$^{2}$) region in the SSA22 protocluster at $z=3.09$ to study the faint dusty star-forming galaxy (DSFG) population. The continuum map achieves an RMS noise level of $\approx25$ $μ$Jy beam$^{-1}$ at $\approx1\arcsec$ spatial resolution, $\approx2\times$ the depth of previous observation of this field. We detected 53 sources with a signal-to-noise ratio above 4.2, doubling the number of detections. Utilizing optical to mid-infrared ancillary data, we search for spectroscopic redshift and identify 18 of 53 as cluster members. For sources with more than two photometric data points in the near-infrared, stellar mass ($M_\star$) and star formation rate (SFR) from spectral energy distribution fitting are presented. The 1.17 mm number count shows $>2\times$ excess at flux density $\gtrsim1$ mJy but are consistent with blank field in fainter flux bins. The monochromatic far-infrared luminosity function of the SSA22 protocluster core region suggests a lack of faint DSFGs. All SSA22 protocluster member galaxies detected at 1.17 mm have SFR within the $M_\star$-SFR relation of general star-forming galaxies. Our results suggest that an early overdense environment like SSA22 protocluster predominantly enhances the formation of massive early-type galaxies in present-day galaxy clusters, but that the star formation in individual member galaxies is likely driven by gas supply along the cosmic web and occurs in a secular way. △ Less

Submitted 24 June, 2025; v1 submitted 30 March, 2025; originally announced March 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 699, A324 (2025)

ADF22-WEB: ALMA and JWST (sub)kpc-scale views of dusty star-forming galaxies in a $z\approx$3 proto-cluster

Authors: Hideki Umehata, Mariko Kubo, Ian Smail, Bret D. Lehmer, Erik B. Monson, Kouichiro Nakanishi, Yuichi Matsuda

Abstract: We present a morphological analysis of ALMA and JWST NIRCam images of nine dusty star-forming galaxies (DSFGs) at zspec=3.09, all embedded within the cosmic web filaments at the SSA22 proto-cluster core. The ALMA 870um and 1.1mm images are obtained at spatial resolutions ranging from 0.5" to 0.05" (350 pc at z=3.09). The high-resolution images enable us to resolve inner structures traced by dust c… ▽ More We present a morphological analysis of ALMA and JWST NIRCam images of nine dusty star-forming galaxies (DSFGs) at zspec=3.09, all embedded within the cosmic web filaments at the SSA22 proto-cluster core. The ALMA 870um and 1.1mm images are obtained at spatial resolutions ranging from 0.5" to 0.05" (350 pc at z=3.09). The high-resolution images enable us to resolve inner structures traced by dust continuum, identifying compact dusty cores, clumps, and offset ridges within bars. Sersic profile fit was performed for both ALMA 870um and NIRCam F444W images at comparable resolutions (0.15"). The Sersic index measured for 870um, masking bright regions, indicates values close to unity, suggesting that dust emission arises from disks with superimposed compact core components. For the JWST F444W images (restframe 1um), the Sersic indices range between nF444W = 1-3, pointing to the coexistence of bulges and stellar disks in these DSFGs. A comparison of dust mass surface density, nF444W, and F200W-F444W color (restframe 0.5-1um) reveals diversity among the DSFGs, likely reflecting different evolutionary stages including some DSFGs with red cores, indicating ongoing rapid bulge growth phases heavily obscured by dust. The predominantly disk-like morphologies observed in most DSFGs in the proto-cluster core contrast sharply with early-type morphologies that dominate the highest density environment in the local universe. This suggests that we are witnessing the early formation of the morphology-density relation, as massive galaxies undergo rapid growth as late-type galaxies fueled by cosmic web gas filaments. △ Less

Submitted 3 February, 2025; originally announced February 2025.

Comments: 21 pages, 12 figures, 5 tables, submitted

ALMA/SCUBA-2 COSMOS Survey: Properties of X-ray- and SED-selected AGNs in Bright Submillimeter Galaxies

Authors: Ryosuke Uematsu, Yoshihiro Ueda, David M. Alexander, A. M. Swinbank, Ian Smail, Carolina Andonie, Chian-Chou Chen, Ugne Dudzeviciute, Soh Ikarashi, Kotaro Kohno, Yuichi Matsuda, Annagrazia Puglisi, Hideki Umehata, Wei-Hao Wang

Abstract: We investigate the properties of active galactic nuclei (AGNs) in the brightest submillimeter galaxies (SMGs) in the COSMOS field. We utilize the bright sample of ALMA/SCUBA-2 COSMOS Survey (AS2COSMOS), which consists of 260 SMGs with $S_{\mathrm{870}\, μ\mathrm{m}}=0.7\text{--}19.2\,\mathrm{mJy}$ at $z=0\text{--}6$. We perform optical to millimeter spectral energy distribution (SED) modeling for… ▽ More We investigate the properties of active galactic nuclei (AGNs) in the brightest submillimeter galaxies (SMGs) in the COSMOS field. We utilize the bright sample of ALMA/SCUBA-2 COSMOS Survey (AS2COSMOS), which consists of 260 SMGs with $S_{\mathrm{870}\, μ\mathrm{m}}=0.7\text{--}19.2\,\mathrm{mJy}$ at $z=0\text{--}6$. We perform optical to millimeter spectral energy distribution (SED) modeling for the whole sample. We identify 24 AGN-host galaxies from the SEDs. Supplemented by 23 X-ray detected AGNs (X-ray AGNs), we construct an overall sample of 40 AGN-host galaxies. The X-ray luminosity upper bounds indicate that the X-ray undetected SED-identified AGNs are likely to be nearly Compton thick or have unusually suppressed X-ray emission. From visual classification, we identify $25^{+6}_{-5}$\% of the SMGs without AGNs as major merger candidates. This fraction is almost consistent with the general galaxy population at $z\sim2$, suggesting that major mergers are not necessarily required for the enhanced star formation in SMGs. We also identify $47^{+16}_{-15}$\% of the AGN hosts as major merger candidates, which is about twice as high as that in the SMGs without AGNs. This suggests that major mergers play a key role in triggering AGN activity in bright SMGs. △ Less

Submitted 15 January, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Comments: 37 pages, 21 figures, accepted for The Astrophysical Journal

The properties of the interstellar medium in dusty, star-forming galaxies at $z \sim 2-4$: The shape of the CO spectral line energy distributions

Authors: Dominic J. Taylor, A. M. Swinbank, Ian Smail, Annagrazia Puglisi, Jack E. Birkin, Ugne Dudzeviciute, Chian-Chou Chen, S. Ikarashi, Marta Frias Castillo, Axel Weiss, Zefeng Li, Scott C. Chapman, Jasper Jansen, E. F. Jimenez-Andrade, Leah K. Morabito, Eric J. Murphy, Matus Rybak, P. P. van der Werf

Abstract: The molecular gas in the interstellar medium (ISM) of star-forming galaxy populations exhibits diverse physical properties. We investigate the $^{12}$CO excitation of twelve dusty, luminous star-forming galaxies at $z \sim 2-4$ by combining observations of the $^{12}$CO from $J_{\rm up} = 1$ to $J_{\rm up} = 8$. The spectral line energy distribution (SLED) has a similar shape to NGC 253, M82, and… ▽ More The molecular gas in the interstellar medium (ISM) of star-forming galaxy populations exhibits diverse physical properties. We investigate the $^{12}$CO excitation of twelve dusty, luminous star-forming galaxies at $z \sim 2-4$ by combining observations of the $^{12}$CO from $J_{\rm up} = 1$ to $J_{\rm up} = 8$. The spectral line energy distribution (SLED) has a similar shape to NGC 253, M82, and local ULIRGs, with much stronger excitation than the Milky Way inner disc. By combining with resolved dust continuum sizes from high-resolution $870$-$μ$m ALMA observations and dust mass measurements determined from multi-wavelength SED fitting, we measure the relationship between the $^{12}$CO SLED and probable physical drivers of excitation: star-formation efficiency, the average intensity of the radiation field $\langle U\rangle$, and the star-formation rate surface density. The primary driver of high-$J_{\rm up}$ $^{12}$CO excitation in star-forming galaxies is star-formation rate surface density. We use the ratio of the CO($3-2$) and CO($6-5$) line fluxes to infer the CO excitation in each source and find that the average ratios for our sample are elevated compared to observations of low-redshift, less actively star-forming galaxies and agree well with predictions from numerical models that relate the ISM excitation to the star-formation rate surface density. The significant scatter in the line ratios of a factor $\approx 3$ within our sample likely reflects intrinsic variations in the ISM properties which may be caused by other effects on the excitation of the molecular gas, such as cosmic ray ionization rates and mechanical heating through turbulence dissipation. △ Less

Submitted 21 November, 2024; originally announced November 2024.

Comments: Accepted for publication in MNRAS; 17 pages, 7 figures

CO(1--0) imaging reveals 10-kiloparsec molecular gas reservoirs around star-forming galaxies at high redshift

Authors: Matus Rybak, J. T. Jansen, M. Frias Castillo, J. A. Hodge, P. P. van der Werf, I. Smail, G. Calistro Rivera, S. Chapman, C. -C. Chen, E. da Cunha, H. Dannerbauer, E. F. Jiménez-Andrade, C. Lagos, C. -L. Liao, E. J. Murphy, D. Scott, A. M. Swinbank, F. Walter

Abstract: Massive, intensely star-forming galaxies at high redshift require a supply of molecular gas from their gas reservoirs, replenished by infall from the surrounding circumgalactic medium, to sustain their immense star-formation rates. However, our knowledge of the extent and morphology of their cold-gas reservoirs is still in its infancy. We present the results of stacking 80 hours of JVLA observat… ▽ More Massive, intensely star-forming galaxies at high redshift require a supply of molecular gas from their gas reservoirs, replenished by infall from the surrounding circumgalactic medium, to sustain their immense star-formation rates. However, our knowledge of the extent and morphology of their cold-gas reservoirs is still in its infancy. We present the results of stacking 80 hours of JVLA observations of CO(1--0) emission -- which traces the cold molecular gas -- in nineteen $z=2.0-4.5$ dusty, star-forming galaxies from the AS2VLA survey. The visibility-plane stack reveals extended emission with a half-light radius of $3.8\pm0.5$~kpc, 2--3$\times$ more extended than the dust-obscured star formation and $1.4\pm0.2\times$ more extended than the stellar emission revealed by JWST. Stacking the [CI](1--0) observations for ten galaxies from our parent sample yields a half-light radius $\leq$2.6~kpc, marginally smaller than CO(1--0). The CO(1--0) size is also comparable to the [CII] halos detected around high-redshift star-forming galaxies, suggesting these arise from molecular gas. Photo-dissociation region modelling indicates that the extended CO(1--0) emission arises from clumpy, dense clouds rather than smooth, diffuse gas. Our results show that the bulk (up to 80\%) of molecular gas resides outside the star-forming region; with only a small part directly contributing to their current star formation. △ Less

Submitted 27 May, 2025; v1 submitted 10 November, 2024; originally announced November 2024.

Comments: Submitted to A&A, second version 2025 May 27. 9 pages, 5 figures

Journal ref: A&A 700, A278 (2025)

ADF22-WEB: A giant barred spiral starburst galaxy in the z = 3.1 SSA22 protocluster core

Authors: H. Umehata, C. C. Steidel, I. Smail, A. M. Swinbank, E. B. Monson, D. Rosario, B. D. Lehmer, K. Nakanishi, M. Kubo, D. Iono, D. M. Alexander, K. Kohno, Y. Tamura, R. J. Ivison, T. Saito, I. Mitsuhashi, S. Huang, Y. Matsuda

Abstract: In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive black holes (SMBHs). However the mechanisms that drive the early growth phase and subsequent transformation of these morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec scale observations of stars, gas, and dust in ADF… ▽ More In the present-day universe, the most massive galaxies are ellipticals located in the cores of galaxy clusters, harboring the heaviest super-massive black holes (SMBHs). However the mechanisms that drive the early growth phase and subsequent transformation of these morphology and kinematics of galaxies remain elusive. Here we report (sub)kiloparsec scale observations of stars, gas, and dust in ADF22.A1, a bright dusty starburst galaxy at z=3.1, hosting a heavily obscured active galactic nucleus and residing in a proto-cluster core. ADF22.A1 is a giant spiral galaxy with the kinematics of a rotating disk with rotation velocity Vrot=530+/-10km/s and diameter larger than 30 kpc. The high specific stellar angular momentum of this system, j*=3400+/-600 kpc km/s, requires a mechanism to effectively spin-up ADF22.A1, indicating the importance of accretion from the cosmic web to supply both gas and angular momentum to galaxies in their early gas-rich starburst phase. In its inner region, gas flows along dust lanes in a bar connected with the bright dusty core and the estimated mass ratio of a bulge to SMBH matches the local relation, suggesting that bars are a key mechanism to shape the early co-evolution of these components. Comparison with cosmological simulations shows that ADF22.A1 will likely evolve into a massive elliptical at the present day, experiencing a significant reduction in angular momentum associated with subsequent galaxy mergers. △ Less

Submitted 6 February, 2025; v1 submitted 29 October, 2024; originally announced October 2024.

Comments: 14 pages, 12 figures. accepted for publication in PASJ

The JWST Emission Line Survey (JELS): An untargeted search for H$α$ emission line galaxies at $z > 6$ and their physical properties

Authors: C. A. Pirie, P. N. Best, K. J. Duncan, D. J. McLeod, R. K. Cochrane, M. Clausen, J. S. Dunlop, S. R. Flury, J. E. Geach, C. L. Hale, E. Ibar, R. Kondapally, Zefeng Li, J. Matthee, R. J. McLure, L. Ossa-Fuentes, A. L. Patrick, Ian Smail, D. Sobral, H. M. O. Stephenson, J. P. Stott, A. M. Swinbank

Abstract: We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7$μ$m, over 63 arcmin$^{2}$ in the PRIMER/COSMOS field, we identified 609 emission line galaxy candidates. From these, we robustly selected 35 H$α$ star-forming galaxies at $z \sim 6.1$, with H$α$ star-formation rates ($\rm{SFR_{Hα}}$) $\sim0.9-15\ \rm{M_{\odot} \ yr^{-1}}$. Co… ▽ More We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7$μ$m, over 63 arcmin$^{2}$ in the PRIMER/COSMOS field, we identified 609 emission line galaxy candidates. From these, we robustly selected 35 H$α$ star-forming galaxies at $z \sim 6.1$, with H$α$ star-formation rates ($\rm{SFR_{Hα}}$) $\sim0.9-15\ \rm{M_{\odot} \ yr^{-1}}$. Combining our unique H$α$ sample with the exquisite panchromatic data in the field, we explored their physical properties and star-formation histories, and compared these to a broad-band selected sample at $z\sim 6$ which offered vital new insights into the nature of high-redshift galaxies. UV-continuum slopes ($β$) were considerably redder for our H$α$ sample ($\langleβ\rangle\sim-1.92$) compared to the broad-band sample ($\langleβ\rangle\sim-2.35$). This was not due to dust attenuation as our H$α$ sample was relatively dust-poor (median $A_V=0.23$); instead, we argued the reddened slopes could be due to nebular continuum. We compared $\rm{SFR_{Hα}}$ and the UV-continuum-derived $\rm{SFR_{UV}}$ to SED-fitted measurements averaged over canonical timescales of 10 and 100 Myr ($\rm{SFR_{10}}$ and $\rm{SFR_{100}}$). We found an increase in recent SFR for our sample of H$α$ emitters, particularly at lower stellar masses ($<10^9 \ \rm{M_{\odot}}$). We also found $\rm{SFR_{Hα}}$ strongly traced SFR averaged over 10 Myr timescales, whereas the UV-continuum over-predicts SFR on 100 Myr timescales at low stellar masses. These results point to our H$α$ sample undergoing `bursty' star formation. Our F356W $z \sim 6$ sample showed a larger scatter in $\rm{SFR_{10}/SFR_{100}}$ across all stellar masses, which highlighted how narrow-band photometric selections of H$α$ emitters are key to quantifying the burstiness of star-formation activity. △ Less

Submitted 30 June, 2025; v1 submitted 15 October, 2024; originally announced October 2024.

Comments: 29 pages, 19 figures, Accepted for publication in MNRAS after minor revisions

The JWST Emission Line Survey (JELS): Extending rest-optical narrow-band emission line selection into the Epoch of Reionization

Authors: K. J. Duncan, D. J. McLeod, P. N. Best, C. A. Pirie, M. Clausen, R. K. Cochrane, J. S. Dunlop, S. R. Flury, J. E. Geach, N. A. Grogin, C. L. Hale, E. Ibar, R. Kondapally, Zefeng Li, J. Matthee, R. J. McLure, Luis Ossa-Fuentes, A. L. Patrick, Ian Smail, D. Sobral, H. M. O. Stephenson, J. P. Stott, A. M. Swinbank

Abstract: We present the JWST Emission Line Survey (JELS), a JWST imaging programme exploiting the wavelength coverage and sensitivity of NIRCam to extend narrow-band rest-optical emission line selection into the epoch of reionization (EoR) for the first time, and to enable unique studies of the resolved ionised gas morphology in individual galaxies across cosmic history. The primary JELS observations compr… ▽ More We present the JWST Emission Line Survey (JELS), a JWST imaging programme exploiting the wavelength coverage and sensitivity of NIRCam to extend narrow-band rest-optical emission line selection into the epoch of reionization (EoR) for the first time, and to enable unique studies of the resolved ionised gas morphology in individual galaxies across cosmic history. The primary JELS observations comprise $\sim4.7μ$m narrow-band imaging over $\sim63$ arcmin$^{2}$ designed to enable selection of H$α$ emitters at z~6.1 and a host of novel emission-line samples, including [OIII] ($z\sim8.3$) and Paschen $α/β$ ($z\sim1.5/2.8$). For the F466N/F470N narrow-band observations, the emission-line sensitivities achieved are up to $\sim2\times$ more sensitive than current slitless spectroscopy surveys (5$σ$ limits of 0.8-1.2$\times10^{-18}\,\text{erg s}^{-1}\text{cm}^{-2}$), corresponding to unobscured H$α$ star-formation rates (SFRs) of 0.9-1.3 $\text{M}_{\odot}\text{yr}^{-1}$ at z~6.1, extending emission-line selections in the EoR to fainter populations. Simultaneously, JELS also adds F200W broadband and F212N narrow-band imaging (H$α$ at z~2.23) that probes SFRs $\gtrsim5\times$ fainter than previous ground-based narrow-band studies ($\sim0.2\text{M}_{\odot}\text{yr}^{-1}$), offering an unprecedented resolved view of star formation at cosmic noon. We present the detailed JELS survey design, key data processing steps specific to the survey observations, and demonstrate the exceptional data quality and imaging sensitivity achieved. We then summarise the key scientific goals of JELS, demonstrate the precision and accuracy of the expected redshift and measured emission line recovery through detailed simulations, and present examples of spectroscopically confirmed H$α$ and [OIII] emitters discovered by JELS that illustrate the novel parameter space probed. △ Less

Submitted 30 June, 2025; v1 submitted 11 October, 2024; originally announced October 2024.

Comments: Now accepted for publication in MRNAS; 19 pages, 11 figures. Significant changes/additions include new mosaics with all reobservations included and detailed simulations on NB photoz and line recovery

Journal ref: Mon Not R Astron Soc (2025) 1329-1347

The MUSE Ultra Deep Field (MUDF) VII. Probing high-redshift gas structures in the surroundings of ALMA-identified massive dusty galaxies

Authors: A. Pensabene, M. Galbiati, M. Fumagalli, M. Fossati, I. Smail, M. Rafelski, M. Revalski, F. Arrigoni-Battaia, A. Beckett, S. Cantalupo, R. Dutta, E. Lusso, T. Lazeyras, G. Quadri, D. Tornotti

Abstract: We present new ALMA continuum and spectral observations of the MUSE Ultra Deep Field (MUDF), a $2\times 2$ arcmin$^2$ region with ultradeep multiwavelength imaging and spectroscopy hosting two bright $z\approx 3.22$ quasars used to study intervening gas structures in absorption. Through a blind search for dusty galaxies, we identified a total of seven high-confidence sources, six of which with sec… ▽ More We present new ALMA continuum and spectral observations of the MUSE Ultra Deep Field (MUDF), a $2\times 2$ arcmin$^2$ region with ultradeep multiwavelength imaging and spectroscopy hosting two bright $z\approx 3.22$ quasars used to study intervening gas structures in absorption. Through a blind search for dusty galaxies, we identified a total of seven high-confidence sources, six of which with secure spectroscopic redshifts. We estimate galaxy dust and stellar masses ($M_{\rm dust}\simeq 10^{7.8-8.6}\,M_{\odot}$, $M_{\star}\simeq 10^{10.2-10.7}\,M_{\odot}$), as well as star formation rates (${\rm SFR}\simeq 10^{1.2-2.0}\,M_{\odot}\,{\rm yr^{-1}} $) which show that most of these galaxies are massive and dust-obscured similar to coeval (sub-)millimeter galaxies. All six spectroscopically-confirmed galaxies are within $500~\rm km~s^{-1}$ of metal absorption lines observed in the quasar sightlines, corresponding to $100\%$ association rate. We also find that four of these galaxies belong to groups in which they are among the most massive members. Within the multiple group galaxies associated to the same absorption system, the ALMA sources are not always the closest in projection, but they are often aligned with the gaseous structures in velocity space. This suggests that these massive galaxies occupy the center of the potential well of the gas structures traced in absorption. However, albeit the low number density of sources identified with ALMA, our study may indicate that absorbers seem to infrequently originate in the inner circumgalactic medium of these galaxies. Instead, they appear to be better tracers of the gas distributed in the large-scale structure that host them. △ Less

Submitted 8 October, 2024; originally announced October 2024.

Comments: 13 pages, 9 figures, 1 Appendix. Submitted to A&A

Journal ref: A&A 696, A33 (2025)

ALESS-JWST: Joint (sub-)kiloparsec JWST and ALMA imaging of $z\sim3$ submillimeter galaxies reveals heavily obscured bulge formation events

Authors: Jacqueline A. Hodge, Elisabete da Cunha, Sarah Kendrew, Juno Li, Ian Smail, Bethany A. Westoby, Omnarayani Nayak, Mark Swinbank, Chian-Chou Chen, Fabian Walter, Paul van der Werf, Misty Cracraft, Andrew Battisti, Willian N. Brandt, Gabriela Calistro Rivera, Scott C. Chapman, Pierre Cox, Helmut Dannerbauer, Roberto Decarli, Marta Frias Castillo, Thomas R. Greve, Kirsten K. Knudsen, Sarah Leslie, Karl M. Menten, Matus Rybak , et al. (3 additional authors not shown)

Abstract: We present JWST NIRCam imaging targeting 13 $z\sim3$ infrared-luminous ($L_{\rm IR}\sim5\times10^{12}L_{\odot}$) galaxies from the ALESS survey with uniquely deep, high-resolution (0.08$''$$-$0.16$''$) ALMA 870$μ$m imaging. The 2.0$-$4.4$μ$m (observed frame) NIRCam imaging reveals the rest-frame near-infrared stellar emission in these submillimeter-selected galaxies (SMGs) at the same (sub-)kpc re… ▽ More We present JWST NIRCam imaging targeting 13 $z\sim3$ infrared-luminous ($L_{\rm IR}\sim5\times10^{12}L_{\odot}$) galaxies from the ALESS survey with uniquely deep, high-resolution (0.08$''$$-$0.16$''$) ALMA 870$μ$m imaging. The 2.0$-$4.4$μ$m (observed frame) NIRCam imaging reveals the rest-frame near-infrared stellar emission in these submillimeter-selected galaxies (SMGs) at the same (sub-)kpc resolution as the 870$μ$m dust continuum. The newly revealed stellar morphologies show striking similarities with the dust continuum morphologies at 870$μ$m, with the centers and position angles agreeing for most sources, clearly illustrating that the spatial offsets reported previously between the 870$μ$m and HST morphologies were due to strong differential dust obscuration. The F444W sizes are 78$\pm$21% larger than those measured at 870$μ$m, in contrast to recent results from hydrodynamical simulations that predict larger 870$μ$m sizes. We report evidence for significant dust obscuration in F444W for the highest-redshift sources, emphasizing the importance of longer-wavelength MIRI imaging. The majority of the sources show evidence that they are undergoing mergers/interactions, including tidal tails/plumes -- some of which are also detected at 870$μ$m. We find a clear correlation between NIRCam colors and 870$μ$m surface brightness on $\sim$1 kpc scales, indicating that the galaxies are primarily red due to dust -- not stellar age -- and we show that the dust structure on $\sim$kpc-scales is broadly similar to that in nearby galaxies. Finally, we find no strong stellar bars in the rest-frame near-infrared, suggesting the extended bar-like features seen at 870$μ$m are highly obscured and/or gas-dominated structures that are likely early precursors to significant bulge growth. △ Less

Submitted 22 July, 2024; originally announced July 2024.

Comments: 26 pages, 10 figures. Submitted to ApJ. Comments welcome

MeerKAT observations of starburst galaxies and AGNs within the core of XMMXCS J2215.9-1738 at $z$ = 1.46

Authors: D. Y. Klutse, M. Hilton, I. Heywood, I. Smail, A. M. Swinbank, K. Knowles, S. P. Sikhosana

Abstract: We present the first detailed radio study of the galaxy cluster XMMXCS J2215.9-1738 at $z$ = 1.46 using MeerKAT $L$-band (1.3 GHz) observations. We combine our radio observation with archival optical and infrared data to investigate the star formation and AGN population within $R_{200}$ ($R = $ 0.8 Mpc) of the cluster centre. Using three selection criteria; the radio luminosity, the far-infrared r… ▽ More We present the first detailed radio study of the galaxy cluster XMMXCS J2215.9-1738 at $z$ = 1.46 using MeerKAT $L$-band (1.3 GHz) observations. We combine our radio observation with archival optical and infrared data to investigate the star formation and AGN population within $R_{200}$ ($R = $ 0.8 Mpc) of the cluster centre. Using three selection criteria; the radio luminosity, the far-infrared radio ratio ($q_{\rm{IR}}$) and the mid-infrared colour, we distinguish galaxies with radio emission predominantly powered by star formation from that powered by AGNs. We selected 24 cluster members within $R_{\rm{200}}$ in the MeerKAT image based on either their photometric or spectroscopic redshift. We classified 12/24 ($50\%$) as galaxies whose radio emission is dominated by star-formation activity, 6/24 ($25\%$) as intermediate star-forming galaxies and 6/24 ($25\%$) as AGN-dominated galaxies. Using the radio continuum luminosities of the star-forming cluster galaxies, we estimated an integrated star formation rate (SFR) value of 1700 $\pm$ 330 M$_{\odot}$yr$^{-1}$ within $R_{200}$. We derived a mass-normalized integrated SFR value of $(570 \pm 110) \times 10^{-14}$ yr$^{-1}$. This supports previous observational and theoretical studies that indicated a rapid increase in star formation activity within the core of high-redshift clusters. We also show that the high AGN fraction within the cluster core is consistent with previous cluster observations at $z >$ 1.5. △ Less

Submitted 4 July, 2024; originally announced July 2024.

A 100 Mpc$^2$ structure traced by hyperluminous galaxies around a massive $z$ = 2.85 protocluster

Authors: George C. P. Wang, Scott C. Chapman, Nikolaus Sulzenauer, Frank Bertoldi, Christopher C. Hayward, Ryley Hill, Satoshi Kikuta, Yuichi Matsuda, Douglas Rennehan, Douglas Scott, Ian Smail, Charles C. Steidel

Abstract: We present wide-field mapping at 850 $μ$m and 450 $μ$m of the $z$ = 2.85 protocluster in the HS1549$+$19 field using the Submillimetre Common User Bolometer Array 2 (SCUBA-2). Spectroscopic follow-up of 18 bright sources selected at 850 $μ$m, using the Nothern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter Array (ALMA), confirms the majority lies near $z$ $\sim$ 2.85 and are likely… ▽ More We present wide-field mapping at 850 $μ$m and 450 $μ$m of the $z$ = 2.85 protocluster in the HS1549$+$19 field using the Submillimetre Common User Bolometer Array 2 (SCUBA-2). Spectroscopic follow-up of 18 bright sources selected at 850 $μ$m, using the Nothern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter Array (ALMA), confirms the majority lies near $z$ $\sim$ 2.85 and are likely members of the structure. Interpreting the spectroscopic redshifts as distance measurements, we find that the SMGs span 90 Mpc$^2$ in the plane of the sky and demarcate a 4100 Mpc$^3$ "pancake"-shaped structure in three dimensions. We find that the high star-formation rates (SFRs) of these SMGs result in a total SFR of 20,000 M$_\odot$ yr$^{-1}$ only from the brightest galaxies in the protocluster. These rapidly star-forming SMGs can be interpreted as massive galaxies growing rapidly at large cluster-centric distances before collapsing into a virialized structure. We find that the SMGs trace the Lyman-$α$ surface density profile. Comparison with simulations suggests that HS1549$+$19 could be building a structure comparable to the most massive clusters in the present-day Universe. △ Less

Submitted 24 June, 2024; originally announced June 2024.

ALMA Lensing Cluster Survey: Physical characterization of near-infrared-dark intrinsically faint ALMA sources at z=2-4

Authors: Akiyoshi Tsujita, Kotaro Kohno, Shuo Huang, Masamune Oguri, Ken-ichi Tadaki, Ian Smail, Hideki Umehata, Zhen-Kai Gao, Wei-Hao Wang, Fengwu Sun, Seiji Fujimoto, Tao Wang, Ryosuke Uematsu, Daniel Espada, Francesco Valentino, Yiping Ao, Franz E. Bauer, Bunyo Hatsukade, Fumi Egusa, Yuri Nishimura, Anton M. Koekemoer, Daniel Schaerer, Claudia Lagos, Miroslava Dessauges-Zavadsky, Gabriel Brammer , et al. (11 additional authors not shown)

Abstract: We present results from Atacama Large Millimeter/submillimeter Array (ALMA) spectral line-scan observations at 3-mm and 2-mm bands of three near-infrared-dark (NIR-dark) galaxies behind two massive lensing clusters MACS J0417.5-1154 and RXC J0032.1+1808. Each of these three sources is a faint (de-lensed $S_{\text{1.2 mm}}$ $<$ 1 mJy) triply lensed system originally discovered in the ALMA Lensing C… ▽ More We present results from Atacama Large Millimeter/submillimeter Array (ALMA) spectral line-scan observations at 3-mm and 2-mm bands of three near-infrared-dark (NIR-dark) galaxies behind two massive lensing clusters MACS J0417.5-1154 and RXC J0032.1+1808. Each of these three sources is a faint (de-lensed $S_{\text{1.2 mm}}$ $<$ 1 mJy) triply lensed system originally discovered in the ALMA Lensing Cluster Survey. We have successfully detected CO and [C I] emission lines and confirmed that their spectroscopic redshifts are $z=3.652$, 2.391, and 2.985. By utilizing a rich multi-wavelength data set, we find that the NIR-dark galaxies are located on the star formation main sequence in the intrinsic stellar mass range of log ($M_*$/$M_\odot$) = 9.8 - 10.4, which is about one order of magnitude lower than that of typical submillimeter galaxies (SMGs). These NIR-dark galaxies show a variety in gas depletion times and spatial extent of dust emission. One of the three is a normal star-forming galaxy with gas depletion time consistent with a scaling relation, and its infrared surface brightness is an order of magnitude smaller than that of typical SMGs. Since this galaxy has an elongated axis ratio of $\sim 0.17$, we argue that normal star-forming galaxies in an edge-on configuration can be heavily dust-obscured. This implies that existing deep WFC3/F160W surveys may miss a fraction of typical star-forming main-sequence galaxies due to their edge-on orientation. △ Less

Submitted 8 February, 2025; v1 submitted 14 June, 2024; originally announced June 2024.

Comments: 23 pages, 10 figures, 5 tables, Accepted for publication on ApJ

The Structure of Massive Star-Forming Galaxies from JWST and ALMA: Dusty, High Redshift Disk Galaxies

Authors: Steven Gillman, Ian Smail, Bitten Gullberg, A. M. Swinbank, Aswin P. Vijayan, Minju Lee, Gabe Brammer, U. Dudzevičiūtė, Thomas R. Greve, Omar Almaini, Malte Brinch, Scott C. Chapman, Chian-Chou Chen, Soh Ikarashi, Yuichi Matsuda, Wei-Hao Wang, Fabian Walter, Paul P. van der Werf

Abstract: We present an analysis of the JWST NIRCam and MIRI morphological properties of 80 massive ($\log_{10}(M_\ast[M_{\odot}])$=11.2$\pm$0.1) dusty star-forming galaxies at $z$$=$2.7$^{+1.2}_{-0.7}$, identified as sub-millimetre galaxies (SMGs) by ALMA, that have been observed as part of the JWST PRIMER project. To compare the structure of these massive, active galaxies to more typical less actively sta… ▽ More We present an analysis of the JWST NIRCam and MIRI morphological properties of 80 massive ($\log_{10}(M_\ast[M_{\odot}])$=11.2$\pm$0.1) dusty star-forming galaxies at $z$$=$2.7$^{+1.2}_{-0.7}$, identified as sub-millimetre galaxies (SMGs) by ALMA, that have been observed as part of the JWST PRIMER project. To compare the structure of these massive, active galaxies to more typical less actively star-forming galaxies, we define two comparison samples. The first of 850 field galaxies matched in specific star-formation rate and redshift and the second of 80 field galaxies matched in stellar mass. We identify 20$\pm$5% of the SMGs as candidate late-stage major mergers, a further 40$\pm$10% as potential minor mergers and 40$\pm$10% which have comparatively undisturbed disk-like morphologies, with no obvious massive neighbours. These rates are comparable to those for the field samples and indicate that the majority of the sub-millimetre-detected galaxies are not late-stage major mergers, but have interaction rates similar to the less-active population at $z$$\sim$2-3. We establish that SMGs have comparable near-infrared sizes to the less active populations, but exhibit lower Sérsic indices, consistent with bulge-less disks and have more structured morphologies at 2$μ$m relative to 4$μ$m. We find evidence for dust reddening as the origin of the morphological differences between the populations, identifying a strong correlation between the F200W$-$F444W pixel colour and the 870$μ$m surface brightness. We conclude that SMGs and less active galaxies at the same epochs share a common disk-like structure, but the weaker bulge components of the SMGs results in a lower dynamical stability. Consequently, instabilities triggered either secularly or by minor external perturbations result in higher levels of activity (and dust content) in SMGs compared to typical star-forming galaxies. [Abridged] △ Less

Submitted 20 September, 2024; v1 submitted 5 June, 2024; originally announced June 2024.

Comments: 23 pages, 13 figures. Accepted for publication in A&A

Journal ref: A&A 691, A299 (2024)

SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). V. Confusion-limited Submillimeter Galaxy Number Counts at 450 $μ$m and Data Release for the COSMOS Field

Authors: Zhen-Kai Gao, Chen-Fatt Lim, Wei-Hao Wang, Chian-Chou Chen, Ian Smail, Scott C. Chapman, Xian Zhong Zheng, Hyunjin Shim, Tadayuki Kodama, Yiping Ao, Siou-Yu Chang, David L. Clements, James S. Dunlop, Luis C. Ho, Yun-Hsin Hsu, Chorng-Yuan Hwang, Ho Seong Hwang, M. P. Koprowski, Douglas Scott, Stephen Serjeant, Yoshiki Toba, Sheona A. Urquhart

Abstract: We present confusion-limited SCUBA-2 450-$μ$m observations in the COSMOS-CANDELS region as part of the JCMT Large Program, SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). Our maps at 450 and 850 $μ$m cover an area of 450 arcmin$^2$. We achieved instrumental noise levels of $σ_{\mathrm{450}}=$ 0.59 mJy beam$^{-1}$ and $σ_{\mathrm{850}}=$ 0.09 mJy beam$^{-1}$ in the deepest area of each map. The co… ▽ More We present confusion-limited SCUBA-2 450-$μ$m observations in the COSMOS-CANDELS region as part of the JCMT Large Program, SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). Our maps at 450 and 850 $μ$m cover an area of 450 arcmin$^2$. We achieved instrumental noise levels of $σ_{\mathrm{450}}=$ 0.59 mJy beam$^{-1}$ and $σ_{\mathrm{850}}=$ 0.09 mJy beam$^{-1}$ in the deepest area of each map. The corresponding confusion noise levels are estimated to be 0.65 and 0.36 mJy beam$^{-1}$. Above the 4 (3.5) $σ$ threshold, we detected 360 (479) sources at 450 $μ$m and 237 (314) sources at 850 $μ$m. We derive the deepest blank-field number counts at 450 $μ$m, covering the flux-density range of 2 to 43 mJy. These are in agreement with other SCUBA-2 blank-field and lensing-cluster observations, but are lower than various model counts. We compare the counts with those in other fields and find that the field-to-field variance observed at 450 $μ$m at the $R=6^\prime$ scale is consistent with Poisson noise, so there is no evidence of strong 2-D clustering at this scale. Additionally, we derive the integrated surface brightness at 450 $μ$m down to 2.1 mJy to be $57.3^{+1.0}_{-6.2}$~Jy deg$^{-2}$, contributing to (41$\pm$4)\% of the 450-$μ$m extragalactic background light (EBL) measured by COBE and Planck. Our results suggest that the 450-$μ$m EBL may be fully resolved at $0.08^{+0.09}_{-0.08}$~mJy, which extremely deep lensing-cluster observations and next-generation submillimeter instruments with large aperture sizes may be able to achieve. △ Less

Submitted 31 May, 2024; originally announced May 2024.

Comments: 29 pages, 14 figures, accepted for publication in ApJ

Beyond MACS: Physical properties of extremely X-ray luminous clusters at $z > 0.5$

Authors: H. Ebeling, J. Richard, B. Beauchesne, Q. Basto, A. C. Edge, I. Smail

Abstract: We present a sample of over 100 highly X-ray luminous galaxy clusters at $z\sim$ 0.5-0.9, discovered by the extended Massive Cluster Survey (eMACS) in ROSAT All-Sky Survey (RASS) data. Follow-up observations of a subset at higher resolution and greater depth with the Chandra X-ray Observatory are used to map the gaseous intra-cluster medium, while strong-gravitational-lensing features identified i… ▽ More We present a sample of over 100 highly X-ray luminous galaxy clusters at $z\sim$ 0.5-0.9, discovered by the extended Massive Cluster Survey (eMACS) in ROSAT All-Sky Survey (RASS) data. Follow-up observations of a subset at higher resolution and greater depth with the Chandra X-ray Observatory are used to map the gaseous intra-cluster medium, while strong-gravitational-lensing features identified in Hubble Space Telescope imaging allow us to constrain the total mass distribution. We present evidence of the exceptional gravitational-lensing power of these massive systems, search for substructure along the line of sight by mapping the radial velocities of cluster members obtained through extensive ground-based spectroscopy, and identify dramatic cases of galaxy evolution in high-density cluster environments. The available observations of the eMACS sample presented here provide a wealth of insights into the properties of very massive clusters ($\gtrsim 10^{15} M_\odot$) at $z > 0.5$, which act as powerful lenses to study galaxies in the very distant Universe. We also discuss the evolutionary state, galaxy population, and large-scale environment of eMACS clusters and release to the community all data and science products to further the understanding of the first generation of truly massive clusters to have formed in the Universe. △ Less

Submitted 17 April, 2024; originally announced April 2024.

Comments: Submitted to MNRAS, comments welcome! A version including the complete appendices is available at http://www.astro.dur.ac.uk/~ace/eMACS.pdf

A Comparative Study of the Ground State Transitions of CO and [C I] as Molecular Gas Tracers at High Redshift

Authors: Marta Frias Castillo, Matus Rybak, Jacqueline A. Hodge, Paul Van der Werk, Ian Smail, Joshua Butterworth, Jasper Jansen, Theodoros Topkaras, Chian-Chou Chen, Scott C. Chapman, Axel Weiss, Hiddo Algera, Jack E. Birkin, Elisabete da Cunha, Jianhang Chen, Helmut Dannerbauer, E. F. Jiménez-Andrade, Soh Ikarashi, Cheng-Lin Liao, Eric J. Murphy, A. M. Swinbank, Fabian Walter, Gabriela Calistro Rivera, R. J. Ivison, Claudia del P. Lagos

Abstract: The CO(1--0) and [\ion{C}{1}](1--0) emission lines are well-established tracers of cold molecular gas mass in local galaxies. At high redshift, where the interstellar medium (ISM) is likely to be denser, there have been limited direct comparisons of both ground state transitions. Here we present a study of CO(1--0) and [\ion{C}{1}](1--0) emission in a sample of 20 unlensed dusty, star-forming gala… ▽ More The CO(1--0) and [\ion{C}{1}](1--0) emission lines are well-established tracers of cold molecular gas mass in local galaxies. At high redshift, where the interstellar medium (ISM) is likely to be denser, there have been limited direct comparisons of both ground state transitions. Here we present a study of CO(1--0) and [\ion{C}{1}](1--0) emission in a sample of 20 unlensed dusty, star-forming galaxies at $z=2-5$. The CO(1--0)/[\ion{C}{1}](1--0) ratio is constant up to at least $z=5$, supporting the use of [CI](1-0) as a gas mass tracer. PDR modelling of the available data indicates a median H$_2$ density of log$(n~[$cm$^{-3}])=4.7\pm0.2$, and UV radiation field log$(G_{\mathrm{UV}} [G$_0$])=3.2\pm0.2$. We use the CO(1--0), [\ion{C}{1}](1--0) and 3mm dust continuum measurements to cross--calibrate the respective gas mass conversion factors, finding no dependence of these factors on either redshift or infrared luminosity. Assuming a variable CO conversion factor then implies [\ion{C}{1}] and dust conversion factors that differ from canonically assumed values but are consistent with the solar/super-solar metallicities expected for our sources. Radiative transfer modelling shows that the warmer CMB at high redshift can significantly affect the [\ion{C}{1}] as well as CO emission, which can change the derived molecular gas masses by up to 70\% for the coldest kinetic gas temperatures expected. Nevertheless, we show that the magnitude of the effect on the ratio of the tracers is within the known scatter of the $L'_\mathrm{CO}-L'_\mathrm{[CI]}$ relation. Further determining the absolute decrease of individual line intensities will require well-sampled spectral line energy distributions (SLEDs) to model the gas excitation conditions in more detail. △ Less

Submitted 8 April, 2024; originally announced April 2024.

The onset of bar formation in a massive galaxy at $z \sim 3.8$

Authors: Aristeidis Amvrosiadis, Samuel Lange, James Nightingale, Qiuhan He, Carlos S. Frenk, Kyle A. Oman, Ian Smail, Mark A. Swinbank, Francesca Fragkoudi, Dimitri A. Gadotti, Shaun Cole, Edoardo Borsato, Andrew Robertson, Richard Massey, Xiaoyue Cao, Ran Li

Abstract: We examine the morphological and kinematical properties of SPT-2147, a strongly lensed, massive, dusty, star-forming galaxy at $z = 3.762$. Combining data from JWST, HST, and ALMA, we study the galaxy's stellar emission, dust continuum and gas properties. The imaging reveals a central bar structure in the stars and gas embedded within an extended disc with a spiral arm-like feature. The kinematics… ▽ More We examine the morphological and kinematical properties of SPT-2147, a strongly lensed, massive, dusty, star-forming galaxy at $z = 3.762$. Combining data from JWST, HST, and ALMA, we study the galaxy's stellar emission, dust continuum and gas properties. The imaging reveals a central bar structure in the stars and gas embedded within an extended disc with a spiral arm-like feature. The kinematics confirm the presence of the bar and of the regularly rotating disc. Dynamical modeling yields a dynamical mass, ${M}_{\rm dyn} = (9.7 \pm 2.0) \times 10^{10}$ ${\rm M}_{\odot}$, and a maximum rotational velocity to velocity dispersion ratio, $V / σ= 9.8 \pm 1.2$. From multi-band imaging we infer, via SED fitting, a stellar mass, ${M}_{\star} = (6.3 \pm 0.9) \times 10^{10}$ $\rm{M}_{\odot}$, and a star formation rate, ${\rm SFR} = 781 \pm 99$ ${\rm M_{\odot} yr^{-1}}$, after correcting for magnification. Combining these measurements with the molecular gas mass, we derive a baryonic-to-total mass ratio of ${M}_{\rm bar} / {M}_{\rm dyn} = 0.9 \pm 0.2$ within 4.0 kpc. This finding suggests that the formation of bars in galaxies begins earlier in the history of the Universe than previously thought and can also occur in galaxies with elevated gas fractions. △ Less

Submitted 2 April, 2024; originally announced April 2024.

Comments: 19 pages, 11 figures. Submitted to MNRAS

Primordial Rotating Disk Composed of $\geq$15 Dense Star-Forming Clumps at Cosmic Dawn

Authors: S. Fujimoto, M. Ouchi, K. Kohno, F. Valentino, C. Giménez-Arteaga, G. B. Brammer, L. J. Furtak, M. Kohandel, M. Oguri, A. Pallottini, J. Richard, A. Zitrin, F. E. Bauer, M. Boylan-Kolchin, M. Dessauges-Zavadsky, E. Egami, S. L. Finkelstein, Z. Ma, I. Smail, D. Watson, T. A. Hutchison, J. R. Rigby, B. D. Welch, Y. Ao, L. D. Bradley , et al. (21 additional authors not shown)

Abstract: Early galaxy formation, initiated by the dark matter and gas assembly, evolves through frequent mergers and feedback processes into dynamically hot, chaotic structures. In contrast, dynamically cold, smooth rotating disks have been observed in massive evolved galaxies merely 1.4 billion years after the Big Bang, suggesting rapid morphological and dynamical evolution in the early Universe. Probing… ▽ More Early galaxy formation, initiated by the dark matter and gas assembly, evolves through frequent mergers and feedback processes into dynamically hot, chaotic structures. In contrast, dynamically cold, smooth rotating disks have been observed in massive evolved galaxies merely 1.4 billion years after the Big Bang, suggesting rapid morphological and dynamical evolution in the early Universe. Probing this evolution mechanism necessitates studies of young galaxies, yet efforts have been hindered by observational limitations in both sensitivity and spatial resolution. Here we report high-resolution observations of a strongly lensed and quintuply imaged, low-luminosity, young galaxy at $z=6.072$ (dubbed the Cosmic Grapes), 930 million years after the Big Bang. Magnified by gravitational lensing, the galaxy is resolved into at least 15 individual star-forming clumps with effective radii of $r_{\rm e}\simeq$ 10--60 parsec (pc), which dominate $\simeq$ 70\% of the galaxy's total flux. The cool gas emission unveils a smooth, underlying rotating disk characterized by a high rotational-to-random motion ratio and a gravitationally unstable state (Toomre $Q \simeq$ 0.2--0.3), with high surface gas densities comparable to local dusty starbursts with $\simeq10^{3-5}$ $M_{\odot}$/pc$^{2}$. These gas properties suggest that the numerous star-forming clumps are formed through disk instabilities with weak feedback effects. The clumpiness of the Cosmic Grapes significantly exceeds that of galaxies at later epochs and the predictions from current simulations for early galaxies. Our findings shed new light on internal galaxy substructures and their relation to the underlying dynamics and feedback mechanisms at play during their early formation phases, potentially explaining the high abundance of bright galaxies observed in the early Universe and the dark matter core-cusp problem. △ Less

Submitted 25 March, 2025; v1 submitted 28 February, 2024; originally announced February 2024.

Comments: Nature Astronomy in press. See also the companion papers on arXiv. Valentino+2024: arXiv:2402.17845 Giménez-Arteaga+2024: arXiv:2402.17875

ALMA Lensing Cluster Survey: Full SED Analysis of z~0.5-6 Lensed Galaxies Detected with Millimeter Observations

Authors: Ryosuke Uematsu, Yoshihiro Ueda, Kotaro Kohno, Yoshiki Toba, Satoshi Yamada, Ian Smail, Hideki Umehata, Seiji Fujimoto, Bunyo Hatsukade, Yiping Ao, Franz Erik Bauer, Gabriel Brammer, Miroslava Dessauges-Zavadsky, Daniel Espada, Jean-Baptiste Jolly, Anton M. Koekemoer, Vasily Kokorev, Georgios E. Magdis, Masamune Oguri, Fengwu Sun

Abstract: Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with ALMA, called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin^2 area and securely detects 180 sources at z~0.5-6 with a flu… ▽ More Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with ALMA, called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin^2 area and securely detects 180 sources at z~0.5-6 with a flux limit of ~0.2 mJy at 1.2 mm (Fujimoto et al. 2023). Here we report the results of multi-wavelength spectral energy distribution (SED) analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources IRX=log(Ldust/LUV)>1), including two extremely dust-obscured galaxies (IRX>5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional SMG samples in the same redshift range. We identify six heavily obscured AGN candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z=2-3 compared with that determined from X-ray surveys below 10 keV. △ Less

Submitted 13 February, 2024; v1 submitted 8 February, 2024; originally announced February 2024.

Comments: 27 pages, 20 figures

Obscured star formation in clusters at z=1.6-2.0: massive galaxy formation and the reversal of the star formation-density relation

Authors: Ian Smail

Abstract: Clusters of galaxies at z>1 are expected to be increasingly active sites of star formation. To test this, an 850um survey was undertaken of eight high-redshift clusters at z=1.6-2.0 using SCUBA-2 on the James Clerk Maxwell Telescope. Mid-infrared properties were used to identify 53 probable counterparts to 45 SCUBA-2 sources with colours that suggested that they were cluster members. This uncovere… ▽ More Clusters of galaxies at z>1 are expected to be increasingly active sites of star formation. To test this, an 850um survey was undertaken of eight high-redshift clusters at z=1.6-2.0 using SCUBA-2 on the James Clerk Maxwell Telescope. Mid-infrared properties were used to identify 53 probable counterparts to 45 SCUBA-2 sources with colours that suggested that they were cluster members. This uncovered a modest overdensity of 850um sources with far-infrared luminosities LIR>10^12Lo (SFR>100Mo/yr) and colours consistent with being cluster members of a factor of 4+/-1 within the central 1Mpc radius of the clusters. The submillimetre photometry of these galaxies was used to estimate the total cluster star formation rates. These showed that the mass-normalised rates in the clusters are two orders of magnitude higher than in local systems, evolving as (1+z)^(5.5+/-0.6). This rapid evolution means that the mass-normalised star formation rates in these clusters matched that of average halos in the field at z~1.8+/-0.2 marking the epoch where the local star formation-density relation reverses in massive halos. The estimated stellar masses of the cluster submillimetre galaxies suggest that their descendants will be amongst the most massive galaxies in z~0 clusters. This reinforces the suggestion that the majority of the massive early-type galaxy population in z~0 clusters were likely to have formed at z>1.5-2 through very active, but dust-obscured, starburst events. △ Less

Submitted 3 March, 2024; v1 submitted 16 January, 2024; originally announced January 2024.

Comments: Revised in response to Referee report

The kinematics of massive high-redshift dusty star-forming galaxies

Authors: A. Amvrosiadis, J. L. Wardlow, J. E. Birkin, I. Smail, A. M. Swinbank, J. Nightingale, F. Bertoldi, W. N. Brandt, C. M. Casey, S. C. Chapman, C. -C. Chen, P. Cox, E. da Cunha, H. Dannerbauer, U. Dudzevičiūtė, B. Gullberg, J. A. Hodge, K. K. Knudsen, K. Menten, F. Walter, P. van der Werf

Abstract: We present a new method for modelling the kinematics of galaxies from interferometric observations by performing the optimization of the kinematic model parameters directly in visibility-space instead of the conventional approach of fitting velocity fields produced with the CLEAN algorithm in real-space. We demonstrate our method on ALMA observations of $^{12}$CO (2$-$1), (3$-$2) or (4$-$3) emissi… ▽ More We present a new method for modelling the kinematics of galaxies from interferometric observations by performing the optimization of the kinematic model parameters directly in visibility-space instead of the conventional approach of fitting velocity fields produced with the CLEAN algorithm in real-space. We demonstrate our method on ALMA observations of $^{12}$CO (2$-$1), (3$-$2) or (4$-$3) emission lines from an initial sample of 30 massive 850$μ$m-selected dusty star-forming galaxies with far-infrared luminosities $\gtrsim$$\,10^{12}\,$L$_{\odot}$ in the redshift range $z \sim\,$1.2$-$4.7. Using the results from our modelling analysis for the 12 sources with the highest signal-to-noise emission lines and disk-like kinematics, we conclude the following: (i) Our sample prefers a CO-to-$H_2$ conversion factor, of $α_{\rm CO} = 0.92 \pm 0.36$; (ii) These far-infrared luminous galaxies follow a similar Tully$-$Fisher relation between the circularized velocity, $V_{\rm circ}$, and baryonic mass, $M_{\rm b}$, as more typical star-forming samples at high redshift, but extend this relation to much higher masses $-$ showing that these are some of the most massive disk-like galaxies in the Universe; (iii) Finally, we demonstrate support for an evolutionary link between massive high-redshift dusty star-forming galaxies and the formation of local early-type galaxies using the both the distributions of the baryonic and kinematic masses of these two populations on the $M_{\rm b}\,-\,σ$ plane and their relative space densities. △ Less

Submitted 14 December, 2023; originally announced December 2023.

An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS Field (AS2COSPEC): Physical Properties of z=2-5 Ultra- and Hyperluminous Infrared Galaxies

Authors: Cheng-Lin Liao, Chian-Chou Chen, Wei-Hao Wang, Ian Smail, Yiping Ao, Scott C. Chapman, Ugne Dudzeviciute, Marta Frias Castillo, Minju M. Lee, Stephen Serjeant, A. Mark Swinbank, Dominic J. Taylor, Hideki Umehata, Yinghe Zhao

Abstract: We report physical properties of the brightest ($S_{870\,μ\rm m}=12.4$-$19.2\,$mJy) and not strongly lensed 18 870$\,μ$m selected dusty star-forming galaxies (DSFGs), also known as submillimeter galaxies (SMGs), in the COSMOS field. This sample is part of an ALMA band$\,$3 spectroscopic survey (AS2COSPEC), and spectroscopic redshifts are measured in 17 of them at $z=2$-$5$. We perform spectral ene… ▽ More We report physical properties of the brightest ($S_{870\,μ\rm m}=12.4$-$19.2\,$mJy) and not strongly lensed 18 870$\,μ$m selected dusty star-forming galaxies (DSFGs), also known as submillimeter galaxies (SMGs), in the COSMOS field. This sample is part of an ALMA band$\,$3 spectroscopic survey (AS2COSPEC), and spectroscopic redshifts are measured in 17 of them at $z=2$-$5$. We perform spectral energy distribution analyses and deduce a median total infrared luminosity of $L_{\rm IR}=(1.3\pm0.1)\times10^{13}\,L_{\odot}$, infrared-based star-formation rate of ${\rm SFR}_{\rm IR}=1390\pm150~M_{\odot}\,\rm yr^{-1}$, stellar mass of $M_\ast=(1.4\pm0.6)\times10^{11}\,M_\odot$, dust mass of $M_{\rm dust}=(3.7\pm0.5)\times10^9\,M_\odot$, and molecular gas mass of $M_{\rm gas}= (α_{\rm CO}/0.8)(1.2\pm0.1)\times10^{11}\,M_\odot$, suggesting that they are one of the most massive, ISM-enriched, and actively star-forming systems at $z=2$-$5$. In addition, compared to less massive and less active galaxies at similar epochs, SMGs have comparable gas fractions; however, they have much shorter depletion time, possibly caused by more active dynamical interactions. We determine a median dust emissivity index of $β=2.1\pm0.1$ for our sample, and by combining our results with those from other DSFG samples, we find no correlation of $β$ with redshift or infrared luminosity, indicating similar dust grain compositions across cosmic time for infrared luminous galaxies. We also find that AS2COSPEC SMGs have one of the highest dust-to-stellar mass ratios, with a median of $0.02\pm0.01$, significantly higher than model predictions, possibly due to too strong of a AGN feedback implemented in the model. Finally, our complete and uniform survey enables us to put constraints on the most massive end of the dust and molecular gas mass functions. △ Less

Submitted 31 January, 2024; v1 submitted 29 November, 2023; originally announced November 2023.

Comments: 25 pages, 13 figures, published in ApJ

Journal ref: ApJ, 961, 226 (2024)

PEARLS: Near Infrared Photometry in the JWST North Ecliptic Pole Time Domain Field

Authors: Christopher N. A. Willmer, Chun Ly, Satoshi Kikuta, S. A. Kattner, Rolf A. Jansen, Seth H. Cohen, Rogier A. Windhorst, Ian Smail, Scott Tompkins, John F. Beacom, Cheng Cheng, Christopher J. Conselice, Brenda L. Frye, Anton M. Koekemoer, Nimish Hathi, Minhee Hyun, Myungshin Im, S. P. Willner, X. Zhao, Walter A. Brisken, F. Civano, William Cotton, Guenther Hasinger, W. Peter Maksym, Marcia J. Rieke , et al. (1 additional authors not shown)

Abstract: We present Near-Infrared (NIR) ground-based Y, J, H, and K imaging obtained in the James Webb Space Telescope North Ecliptic Pole Time Domain Field (TDF) using the MMT-Magellan Infrared Imager and Spectrometer (MMIRS) on the MMT.These new observations cover a field of approximately 230 arcmin^2 in Y, H, and K and 313 arcmin^2 in J. Using Monte Carlo simulations we estimate a 1 sigma depth relative… ▽ More We present Near-Infrared (NIR) ground-based Y, J, H, and K imaging obtained in the James Webb Space Telescope North Ecliptic Pole Time Domain Field (TDF) using the MMT-Magellan Infrared Imager and Spectrometer (MMIRS) on the MMT.These new observations cover a field of approximately 230 arcmin^2 in Y, H, and K and 313 arcmin^2 in J. Using Monte Carlo simulations we estimate a 1 sigma depth relative to the background sky of (Y, J, H, K}) = (23.80, 23.53, 23.13, 23.28) in AB magnitudes for point sources at a 95% completeness level. These observations are part of the ground-based effort to characterize this region of the sky, supplementing space-based data obtained with Chandra, NuSTAR, XMM, AstroSat, HST, and JWST. This paper describes the observations and reduction of the NIR imaging and combines these NIR data with archival imaging in the visible, obtained with the Subaru Hyper-Suprime-Cam, to produce a merged catalog of 57,501 sources. The new observations reported here, plus the corresponding multi-wavelength catalog, will provide a baseline for time-domain studies of bright sources in the TDF. △ Less

Submitted 5 September, 2023; v1 submitted 31 August, 2023; originally announced September 2023.

Comments: 23 pages, 10 figures. Accepted for publication in ApJS. Images and catalogs available at https://doi.org/10.5281/zenodo.7934393. Data description available under ancillary files and at the Zenodo site. Added a reference, fixed typos in metadata

Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter galaxy that is invisible to HST

Authors: Ian Smail, Ugne Dudzeviciute, Mark Gurwell, Giovanni G. Fazio, S. P. Willner, A. M. Swinbank, Vinodiran Arumugam, Jake Summers, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Ashish Meena, Adi Zitrin, William C. Keel, Dan Coe, Christopher J. Conselice, Jordan C. J. D'Silva, Simon P. Driver, Brenda Frye, Norman A. Grogin, Anton M. Koekemoer, Madeline A. Marshall, Mario Nonino, Nor Pirzkal, Aaron Robotham , et al. (10 additional authors not shown)

Abstract: We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A1489. These SMA-located sources both lie at z=4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam observations. We… ▽ More We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A1489. These SMA-located sources both lie at z=4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam observations. We investigate their stellar, ISM, and dynamical properties, including a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass and Av maps. We find that 850.1 is one of the most massive and highly obscured, Av~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and 850.2 is one of the least massive and least obscured, Av~1, members of the z>4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on imaging at <2um, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar mass distribution, Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both the properties of massive, quiescent galaxies at z~1.5 and ultra-massive early-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature which we link to the active dynamical environment it resides within. △ Less

Submitted 28 June, 2023; originally announced June 2023.

Comments: Submitted to ApJ, comments welcome!

Unbiased surveys of dust-enshrouded galaxies using ALMA

Authors: K. Kohno, S. Fujimoto, A. Tsujita, V. Kokorev, G. Brammer, G. E. Magdis, F. Valentino, N. Laporte, Fengwu Sun, E. Egami, F. E. Bauer, A. Guerrero, N. Nagar, K. I. Caputi, G. B. Caminha, J. -B. Jolly, K. K. Knudsen, R. Uematsu, Y. Ueda, M. Oguri, A. Zitrin, M. Ouchi, Y. Ono, J. Gonzalez-Lopez, J. Richard , et al. (21 additional authors not shown)

Abstract: The ALMA lensing cluster survey (ALCS) is a 96-hr large program dedicated to uncovering and characterizing intrinsically faint continuum sources and line emitters with the assistance of gravitational lensing. All 33 cluster fields were selected from HST/Spitzer treasury programs including CLASH, Hubble Frontier Fields, and RELICS, which also have Herschel and Chandra coverages. The total sky area… ▽ More The ALMA lensing cluster survey (ALCS) is a 96-hr large program dedicated to uncovering and characterizing intrinsically faint continuum sources and line emitters with the assistance of gravitational lensing. All 33 cluster fields were selected from HST/Spitzer treasury programs including CLASH, Hubble Frontier Fields, and RELICS, which also have Herschel and Chandra coverages. The total sky area surveyed reaches $\sim$133 arcmin$^2$ down to a depth of $\sim$60 $μ$Jy beam$^{-1}$ (1$σ$) at 1.2 mm, yielding 141 secure blind detections of continuum sources and additional 39 sources aided by priors. We present scientific motivation, survey design, the status of spectroscopy follow-up observations, and number counts down to $\sim$7 $μ$Jy. Synergies with JWST are also discussed. △ Less

Submitted 24 May, 2023; originally announced May 2023.

Comments: 6 pages, 4 figures, Proceedings of the 7th Chile-Cologne-Bonn-Symposium: Physics and Chemistry of Star Formation, V. Ossenkopf-Okada, R. Schaaf, I. Breloy (eds.)

ALMA Lensing Cluster Survey: Deep 1.2 mm Number Counts and Infrared Luminosity Functions at $z\simeq1-8$

Authors: Seiji Fujimoto, Kotaro Kohno, Masami Ouchi, Masamune Oguri, Vasily Kokorev, Gabriel Brammer, Fengwu Sun, Jorge Gonzalez-Lopez, Franz E. Bauer, Gabriel B. Caminha, Bunyo Hatsukade, Johan Richard, Ian Smail, Akiyoshi Tsujita, Yoshihiro Ueda, Ryosuke Uematsu, Adi Zitrin, Dan Coe, Jean-Paul Kneib, Marc Postman, Keiichi Umetsu, Claudia del P. Lagos, Gergo Popping, Yiping Ao, Larry Bradley , et al. (18 additional authors not shown)

Abstract: We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescop… ▽ More We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $μ$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects. △ Less

Submitted 20 June, 2024; v1 submitted 2 March, 2023; originally announced March 2023.

Comments: ApJS in press, 34 pages, 8 Tables, and 18 Figures (+38 pages, 5 Tables, and 6 Figures in Appendix)

VLA Legacy Survey of Molecular Gas in Massive Star-forming Galaxies at High Redshift

Authors: Marta Frias Castillo, Jacqueline Hodge, Matus Rybak, Paul van der Werf, Ian Smail, Jack Birkin, Chian-Chou Chen, Scott Chapman, Ryley Hill, Claudia del P. Lagos, Cheng-Lin Liao, Elisabete da Cunha, Gabriela Calistro Rivera, Jianhang Chen, Eric Jimenez Andrade, Eric Murphy, Douglas Scott, Mark Swinbank, Fabian Walter, Rob Ivison, Helmut Dannerbauer

Abstract: We present initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO($J$ = 1-0) transition in a sample of 30 submillimeter-selected, dusty star-forming galaxies at $z =$ 2-5 with existing mid--$J$ CO detections from ALMA and NOEMA, of which 17 have been fully observed. We detect CO(1-0) emission in 11 targets, along with three tentative ($\sim$1.5-2$σ$) detecti… ▽ More We present initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO($J$ = 1-0) transition in a sample of 30 submillimeter-selected, dusty star-forming galaxies at $z =$ 2-5 with existing mid--$J$ CO detections from ALMA and NOEMA, of which 17 have been fully observed. We detect CO(1-0) emission in 11 targets, along with three tentative ($\sim$1.5-2$σ$) detections; three galaxies are undetected. Our results yield total molecular gas masses of 6-23$\times$10$^{10}$ ($α_\mathrm{CO}$/1) M$_\odot$, with gas mass fractions, $f_\mathrm{gas}$=$M_\mathrm{mol}$/($M_*$+$M_\mathrm{mol}$), of 0.1-0.8 and a median depletion time of (140$\pm$70) Myr. We find median CO excitation ratios of $r_{31}$ = 0.75$\pm$0.39 and $r_{41}$ = 0.63$\pm$0.44, with a significant scatter. We find no significant correlation between the excitation ratio and a number of key parameters such as redshift, CO(1-0) line width or $Σ_\mathrm{SFR}$. We only find a tentative positive correlation between $r_{41}$ and the star-forming efficiency, but we are limited by our small sample size. Finally, we compare our results to predictions from the SHARK semi-analytical model, finding a good agreement between the molecular gas masses, depletion times and gas fractions of our sources and their SHARK counterparts. Our results highlight the heterogeneous nature of the most massive star-forming galaxies at high-redshift, and the importance of CO(1--0) observations to robustly constrain their total molecular gas content and ISM properties. △ Less

Submitted 10 February, 2023; v1 submitted 7 February, 2023; originally announced February 2023.

Comments: 10 pages, 15 figures. Accepted for publication in ApJ

KAOSS: turbulent, but disc-like kinematics in dust-obscured star-forming galaxies at $z\sim$1.3-2.6

Authors: Jack E. Birkin, A. Puglisi, A. M. Swinbank, Ian Smail, Fang Xia An, S. C. Chapman, Chian-Chou Chen, C. J. Conselice, U. Dudzevičiūtė, D. Farrah, B. Gullberg, Y. Matsuda, E. Schinnerer, D. Scott, J. L. Wardlow, P. van der Werf

Abstract: We present spatially resolved kinematics of 27 ALMA-identified dust-obscured star-forming galaxies (DSFGs) at $z\sim$1.3-2.6, as traced by H$α$ emission using VLT/KMOS near-infrared integral field spectroscopy from the "KMOS-ALMA Observations of Submillimetre Sources" (KAOSS) Large Programme. We derive H$α$ rotation curves and velocity dispersion profiles for the DSFGs, and find that among the 27… ▽ More We present spatially resolved kinematics of 27 ALMA-identified dust-obscured star-forming galaxies (DSFGs) at $z\sim$1.3-2.6, as traced by H$α$ emission using VLT/KMOS near-infrared integral field spectroscopy from the "KMOS-ALMA Observations of Submillimetre Sources" (KAOSS) Large Programme. We derive H$α$ rotation curves and velocity dispersion profiles for the DSFGs, and find that among the 27 sources with bright, spatially extended H$α$ emission, 24 display evidence for disc-like kinematics. We measure a median inclination-corrected velocity at 2.2$R_{\rm d}$ of $v_{\rm rot}=$190$\pm$40kms$^{-1}$ and intrinsic velocity dispersion of $σ_0=$87$\pm$6kms$^{-1}$ for these disc-like sources. The kinematics yield median circular velocities of $v_{\rm circ}=$230$\pm$20kms$^{-1}$ and dynamical masses within 2$R_{\rm e}$ ($\sim$7kpc radius) of $M_{\rm dyn}=$(1.1$\pm$0.2)$\times$10$^{11}$M$_\odot$. Compared to less actively star-forming galaxies, KAOSS DSFGs are both faster rotating with higher intrinsic velocity dispersions, but have similar $v_{\rm rot}/σ_0$ ratios, median $v/σ_0=$2.5$\pm$0.5. We suggest that the kinematics of the DSFGs are primarily rotation supported but with a non-negligible contribution from pressure support, which may be driven by star formation or mergers/interactions. We estimate the normalisation of the stellar mass Tully-Fisher relation (sTFR) for the disc-like DSFGs and compare it with local studies, finding no evolution at fixed slope between $z\sim$2 and $z\sim$0. Finally, we show that the kinematic properties of the DSFG population are consistent with them evolving into massive early-type galaxies, the dominant $z\sim$0 population at these masses. △ Less

Submitted 1 May, 2024; v1 submitted 13 January, 2023; originally announced January 2023.

Comments: 24 pages, 15 figures, accepted for publication in MNRAS, updated author list

The JCMT SCUBA-2 Survey of the James Webb Space Telescope North Ecliptic Pole Time-Domain Field

Authors: Minhee Hyun, Myungshin Im, Ian R. Smail, William D. Cotton, Jack E. Birkin, Satoshi Kikuta, Hyunjin Shim, Christopher N. A. Willmer, James J. Condon, Rogier A. Windhorst, Seth H. Cohen, Rolf A. Jansen, Chun Ly, Yuichi Matsuda, Giovanni G. Fazio, A. M. Swinbank, Haojing Yan

Abstract: The James Webb Space Telescope Time-Domain Field (JWST-TDF) is an $\sim$14$'$ diameter field near the North Ecliptic Pole that will be targeted by one of the JWST Guaranteed Time Observations programs. Here, we describe our James Clerk Maxwell Telescope SCUBA-2 850 $μ$m imaging of the JWST-TDF and present the submillimeter source catalog and properties. We also present a catalog of radio sources f… ▽ More The James Webb Space Telescope Time-Domain Field (JWST-TDF) is an $\sim$14$'$ diameter field near the North Ecliptic Pole that will be targeted by one of the JWST Guaranteed Time Observations programs. Here, we describe our James Clerk Maxwell Telescope SCUBA-2 850 $μ$m imaging of the JWST-TDF and present the submillimeter source catalog and properties. We also present a catalog of radio sources from Karl J. Jansky Very Large Array 3 GHz observations of the field. These observations were obtained to aid JWST's study of the dust-obscured galaxies that contribute significantly to the cosmic star formation at high redshifts. Our deep 850 $μ$m map covers the JWST TDF at a noise level of $σ_{850}$ = 1.0 mJy beam$^{-1}$, detecting 83/31 sources in the main/supplementary signal-to-noise ratio (S/N $>$ 4 / S/N = 3.5 - 4) sample respectively. The 3 GHz observations cover a 24$'$ diameter field with a 1 $σ$ noise of 1$μ$Jy beam$^{-1}$ at a 0$.\!\!^{\prime\prime}$7 FWHM. We identified eighty-five 3 GHz counterparts to sixty-six 850 $μ$m sources and then matched these with multiwavelength data from the optical to the mid-infrared wave bands. We performed spectral energy distribution fitting for 61 submillimeter galaxies (SMGs) matched with optical/near-infrared data, and found that SMGs at S/N $>$ 4 have a median value of $z_{phot} = $2.22 $\pm$ 0.12, star formation rates of 300 $\pm$ 40 M$_{\odot}\,{\rm yr^{-1}}$ (Chabrier initial mass function), and typical cold dust masses of 5.9 $\pm$ 0.7 $ \times$ 10$^{8} $M$_{\odot}$, in line with bright SMGs from other surveys. The large cold dust masses indicate correspondingly large cool gas masses, which we suggest are a key factor necessary to drive the high star formation rates seen in this population △ Less

Submitted 7 January, 2023; originally announced January 2023.

Comments: 22 pages, 18 figures (1 extended figure and the full catalog are included), Published in ApJS

Journal ref: ApJS 264 19 (2023)

ALMACAL IX: multi-band ALMA survey for dusty star-forming galaxies and the resolved fractions of the cosmic infrared background

Authors: Jianhang Chen, R. J. Ivison, Martin A. Zwaan, Ian Smail, Anne Klitsch, Céline Péroux, Gergö Popping, Andrew D. Biggs, Roland Szakacs, Aleksandra Hamanowicz, Claudia Lagos

Abstract: Wide, deep, blind continuum surveys at submillimetre/millimetre (submm/mm) wavelengths are required to provide a full inventory of the dusty, distant Universe. However, conducting such surveys to the necessary depth, with sub-arcsec angular resolution, is prohibitively time-consuming, even for the most advanced submm/mm telescopes. Here, we report the most recent results from the ALMACAL project,… ▽ More Wide, deep, blind continuum surveys at submillimetre/millimetre (submm/mm) wavelengths are required to provide a full inventory of the dusty, distant Universe. However, conducting such surveys to the necessary depth, with sub-arcsec angular resolution, is prohibitively time-consuming, even for the most advanced submm/mm telescopes. Here, we report the most recent results from the ALMACAL project, which exploits the 'free' calibration data from the Atacama Large Millimetre/submillimetre Array (ALMA) to map the lines of sight towards and beyond the ALMA calibrators. ALMACAL has now covered 1,001 calibrators, with a total sky coverage around 0.3 deg2, distributed across the sky accessible from the Atacama desert, and has accumulated more than 1,000h of integration. The depth reached by combining multiple visits to each field makes ALMACAL capable of searching for faint, dusty, star-forming galaxies (DSFGs), with detections at multiple frequencies to constrain the emission mechanism. Based on the most up-to-date ALMACAL database, we report the detection of 186 DSFGs with flux densities down to S870um ~ 0.2mJy, comparable with existing ALMA large surveys but less susceptible to cosmic variance. We report the number counts at five wavelengths between 870um and 3mm, in ALMA bands 3, 4, 5, 6 and 7, providing a benchmark for models of galaxy formation and evolution. By integrating the observed number counts and the best-fitting functions, we also present the resolved fraction of the cosmic infrared background (CIB) and the CIB spectral shape. Combining existing surveys, ALMA has currently resolved about half of the CIB in the submm/mm regime. △ Less

Submitted 28 November, 2022; v1 submitted 17 October, 2022; originally announced October 2022.

Comments: 22 pages, 16 figures, accepted for publication in MNRAS

Journal ref: 2023MNRAS.518.1378C

Resolving a merger in a hyper-luminous submillimeter galaxy at z=2.82

Authors: R. W. Perry, S. C. Chapman, Ian Smail, F. Bertoldi

Abstract: We present the resolved properties of the $z=2.82$ Hyper Luminous Infrared Galaxy (HyLIRG) HS170850.1, the brightest 850$μ$m source found in the SCUBA-2 followup to the Keck Baryonic Structure Survey fields (S$_{\rm 850 μm}=$19.5 mJy), and amongst the most luminous starbursts known at any redshift. Using the IRAM-NOEMA interferometer in the highest resolution A-configuration, we resolve the source… ▽ More We present the resolved properties of the $z=2.82$ Hyper Luminous Infrared Galaxy (HyLIRG) HS170850.1, the brightest 850$μ$m source found in the SCUBA-2 followup to the Keck Baryonic Structure Survey fields (S$_{\rm 850 μm}=$19.5 mJy), and amongst the most luminous starbursts known at any redshift. Using the IRAM-NOEMA interferometer in the highest resolution A-configuration, we resolve the source into two components separated by $\sim$8 kpc, visible as blue shifted and red shifted $^{12}$CO(5-4) lines, exhibiting the expected kinematic properties of a major merger between two gas-rich galaxies. The combined merger system is traced over 2.3$''$ or 18.3 kpc. Each component of the merger shows ordered gas motions suggestive of a massive, turbulent disk. We measure the masses of the blue and red disks as (1.5 $\pm$ 0.2) $\times10^{11}$ M$_\odot$ and (0.71 $\pm$ 0.22) $\times10^{11}$ M$_\odot$ respectively. The more massive disk component shows broad wings in the CO line, offset by $\sim$3 kpc from the disk centroid along the major axis, and extending to velocities $\sim\pm$1000 km $ \rm{s^{-1}}$ from systemic velocity. We interpret this as either a possible bipolar outflowing component, or more likely a warping or tidal structure in the CO disk. Comparing the properties of HS170850.1 to other submillimeter detected galaxies with comparably bright 850$μ$m luminosities suggests that ongoing gas-rich mergers, or at least a clustered/group environment lead to these most extreme starburst phases. △ Less

Submitted 3 June, 2023; v1 submitted 15 October, 2022; originally announced October 2022.

Comments: 13 pages, 5 Figures, 2 Tables

JWST's PEARLS: A JWST/NIRCam view of ALMA sources

Authors: Cheng Cheng, Jia-Sheng Huang, Ian Smail, Haojing Yan, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Zhiyuan Ma, Anton Koekemoer, Christopher N. A. Willmer, S. P. Willner, Jose M. Diego, Brenda Frye, Christopher J. Conselice, Leonardo Ferreira, Andreea Petric, Min Yun, Hansung B. Gim, Maria del Carmen Polletta, Kenneth J. Duncan, Rachel Honor, Benne W. Holwerda, Huub J. A. Röttgering, Nimish P. Hathi, Patrick S. Kamieneski , et al. (11 additional authors not shown)

Abstract: We report the results of James Webb Space Telescope/NIRCam observations of 19 (sub)millimeter (submm/mm) sources detected by the Atacama Large Millimeter Array (ALMA). The accurate ALMA positions allowed unambiguous identifications of their NIRCam counterparts. Taking gravitational lensing into account, these represent 16 distinct galaxies in three fields and constitute the largest sample of its k… ▽ More We report the results of James Webb Space Telescope/NIRCam observations of 19 (sub)millimeter (submm/mm) sources detected by the Atacama Large Millimeter Array (ALMA). The accurate ALMA positions allowed unambiguous identifications of their NIRCam counterparts. Taking gravitational lensing into account, these represent 16 distinct galaxies in three fields and constitute the largest sample of its kind to date. The counterparts' spectral energy distributions from rest-frame ultraviolet to near infrared provide photometric redshifts ($1<z<4.5$) and stellar masses ($M_*>10^{10.5}$ Msol), which are similar to sub-millimeter galaxy (SMG) hosts studied previously. However, our sample is fainter in submm/mm than the classic SMG samples are, and our sources exhibit a wider range of properties. They have dust-embedded star-formation rates as low as 10 Msol yr$^{-1}$, and the sources populate both the star-forming main sequence and the quiescent categories. The deep NIRCam data allow us to study the rest-frame near-IR morphologies. Excluding two multiply imaged systems and one quasar, the majority of the remaining sources are disk-like and show either little or no disturbance. This suggests that secular growth is a potential route for the assembly of high-mass disk galaxies. While a few hosts have large disks, the majority have small disks (median half-mass radius of 1.6 kpc). At this time, it is unclear whether this is due to the prevalence of small disks at these redshifts or some unknown selection effects of deep ALMA observations. A larger sample of ALMA sources with NIRCam observations will be able to address this question. △ Less

Submitted 9 December, 2022; v1 submitted 14 October, 2022; originally announced October 2022.

Comments: 19 pages, 11 figures, accepted by ApJL

JWST's PEARLS: Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results

Authors: Rogier A. Windhorst, Seth H. Cohen, Rolf A. Jansen, Jake Summers, Scott Tompkins, Christopher J. Conselice, Simon P. Driver, Haojing Yan, Dan Coe, Brenda Frye, Norman Grogin, Anton Koekemoer, Madeline A. Marshall, Rosalia O'Brien, Nor Pirzkal, Aaron Robotham, Russell E. Ryan, Jr., Christopher N. A. Willmer, Timothy Carleton, Jose M. Diego, William C. Keel, Paolo Porto, Caleb Redshaw, Sydney Scheller, Stephen M. Wilkins , et al. (60 additional authors not shown)

Abstract: We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" ("PEARLS") project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift proto-clusters;… ▽ More We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" ("PEARLS") project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift proto-clusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, AGN growth, and First Light. Five fields, the JWST NEP Time-Domain Field (TDF), IRAC Dark Field (IDF), and three lensing clusters, will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9-4.5 $μ$m galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9-4.5 μm. PEARLS is designed to be of lasting benefit to the community. △ Less

Submitted 28 November, 2022; v1 submitted 9 September, 2022; originally announced September 2022.

Comments: Accepted to AJ, comments welcome. We ask anyone who uses our public PEARLS (NEP TDF) data to refer to this overview paper

ALMA Lensing Cluster Survey: ALMA-Herschel Joint Study of Lensed Dusty Star-Forming Galaxies across $z\simeq0.5-6$

Authors: Fengwu Sun, Eiichi Egami, Seiji Fujimoto, Timothy Rawle, Franz E. Bauer, Kotaro Kohno, Ian Smail, Pablo G. Pérez-González, Yiping Ao, Scott C. Chapman, Francoise Combes, Miroslava Dessauges-Zavadsky, Daniel Espada, Jorge González-López, Anton M. Koekemoer, Vasily Kokorev, Minju M. Lee, Kana Morokuma-Matsui, Alejandra M. Muñoz Arancibia, Masamune Oguri, Roser Pelló, Yoshihiro Ueda, Ryosuke Uematsu, Francesco Valentino, Paul Van der Werf , et al. (3 additional authors not shown)

Abstract: We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100-500 $μ$m are deblended for 180 ALMA sources in 33 lensing cluster fields that are either detected securely (141 sources; in our main sample) or tentatively at S/N$\geq$4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15-mm flux… ▽ More We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100-500 $μ$m are deblended for 180 ALMA sources in 33 lensing cluster fields that are either detected securely (141 sources; in our main sample) or tentatively at S/N$\geq$4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15-mm flux density of $\sim0.02$ mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at $>2σ$ in at least one Herschel band. 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at $z=4.2\pm1.2$. The 16-50-84 percentiles of the redshift distribution are 1.15-2.08-3.59 for ALCS sources in the main sample, suggesting an increasing fraction of $z\simeq1-2$ galaxies among fainter millimeter sources ($f_{1150}\sim 0.1$ mJy). With a median lensing magnification factor of $μ= 2.6_{-0.8}^{+2.6}$, ALCS sources in the main sample exhibit a median intrinsic star-formation rate of $94_{-54}^{+84}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of $\sim$3. Our study suggests weak or no redshift evolution of dust temperature with $L_\mathrm{IR}<10^{12}\,\mathrm{L}_\odot$ galaxies within our sample at $z \simeq 0 - 2$. At $L_\mathrm{IR}>10^{12}\,\mathrm{L}_\odot$, the dust temperatures show no evolution across $z \simeq 1 -4$ while being lower than those in the local Universe. For the highest-redshift source in our sample ($z=6.07$), we can rule out an extreme dust temperature ($>$80 K) that was reported for MACS0416 Y1 at $z=8.31$. △ Less

Submitted 7 May, 2022; v1 submitted 14 April, 2022; originally announced April 2022.

Comments: 44 pages, 23 figures, 4 tables, accepted for publication in ApJ

An ultra-deep multi-band VLA survey of the faint radio sky (COSMOS-XS): New constraints on the cosmic star formation history

Authors: D. van der Vlugt, J. A. Hodge, H. S. B. Algera, I. Smail, S. K. Leslie, J. F. Radcliffe, D. A. Riechers, H. Röttgering

Abstract: We make use of ultra-deep 3 GHz Karl G. Jansky Very Large Array observations of the COSMOS field from the multi-band COSMOS-XS survey to infer radio luminosity functions (LFs) of star-forming galaxies (SFGs). Using $\sim$1300 SFGs with redshifts out to $z\sim4.6$, and fixing the faint and bright end shape of the radio LF to the local values, we find a strong redshift trend that can be fitted by pu… ▽ More We make use of ultra-deep 3 GHz Karl G. Jansky Very Large Array observations of the COSMOS field from the multi-band COSMOS-XS survey to infer radio luminosity functions (LFs) of star-forming galaxies (SFGs). Using $\sim$1300 SFGs with redshifts out to $z\sim4.6$, and fixing the faint and bright end shape of the radio LF to the local values, we find a strong redshift trend that can be fitted by pure luminosity evolution with the luminosity parameter given by $α_L \propto (3.40 \pm 0.11) - (0.48 \pm 0.06)z$. We then combine the ultra-deep COSMOS-XS data-set with the shallower VLA-COSMOS $\mathrm{3\,GHz}$ large project data-set over the wider COSMOS field in order to fit for joint density+luminosity evolution, finding evidence for significant density evolution. By comparing the radio LFs to the observed far-infrared (FIR) and ultraviolet (UV) LFs, we find evidence of a significant underestimation of the UV LF by $21.6\%\, \pm \, 14.3 \, \%$ at high redshift ($3.3\,<\,z\,<\,4.6$, integrated down to $0.03\,L^{\star}_{z=3}$). We derive the cosmic star formation rate density (SFRD) by integrating the fitted radio LFs and find that the SFRD rises up to $z\,\sim\,1.8$ and then declines more rapidly than previous radio-based estimates. A direct comparison between the radio SFRD and a recent UV-based SFRD, where we integrate both LFs down to a consistent limit ($0.038\,L^{\star}_{z=3}$), reveals that the discrepancy between the radio and UV LFs translates to a significant ($\sim$1 dex) discrepancy in the derived SFRD at $z>3$, even assuming the latest dust corrections and without accounting for optically dark sources. △ Less

Submitted 8 April, 2022; originally announced April 2022.

Comments: Submitted to ApJ; 27 pages, 13 figures, 4 tables

An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS field (AS2COSPEC): Survey Description and First Results

Authors: Chian-Chou Chen, Cheng-Lin Liao, Ian Smail, A. M. Swinbank, Y. Ao, A. J. Bunker, S. C. Chapman, B. Hatsukade, R. J. Ivison, Minju M. Lee, Stephen Serjeant, Hideki Umehata, Wei-Hao Wang, Y. Zhao

Abstract: We introduce an ALMA band 3 spectroscopic survey, targeting the brightest submillimeter galaxies (SMGs) in the COSMOS field. Here we present the first results based on the 18 primary SMGs that have 870 $μ$m flux densities of $S_{870}=12.4-19.3$ mJy and are drawn from a parent sample of 260 ALMA-detected SMGs from the AS2COSMOS survey. We detect emission lines in 17 and determine their redshifts to… ▽ More We introduce an ALMA band 3 spectroscopic survey, targeting the brightest submillimeter galaxies (SMGs) in the COSMOS field. Here we present the first results based on the 18 primary SMGs that have 870 $μ$m flux densities of $S_{870}=12.4-19.3$ mJy and are drawn from a parent sample of 260 ALMA-detected SMGs from the AS2COSMOS survey. We detect emission lines in 17 and determine their redshifts to be in the range of $z=2-5$ with a median of ${3.3\pm0.3}$. We confirm that SMGs with brighter $S_{870}$ are located at higher redshifts. The data additionally cover five fainter companion SMGs, and we obtain line detection in one. Together with previous studies, our results indicate that for SMGs that satisfy our selection, their brightest companion SMGs are physically associated with their corresponding primary SMGs in $\ge40$% of the time, suggesting that mergers play a role in the triggering of star formation. By modeling the foreground gravitational fields, $<10$% of the primary SMGs can be strongly lensed with a magnification $μ>2$. We determine that about 90\% of the primary SMGs have lines that are better described by double Gaussian profiles, and the median separation of the two Gaussian peaks is 430$\pm$40 km s$^{-1}$. This allows estimates of an average baryon mass, which together with the line dispersion measurements puts our primary SMGs on the similar mass-$σ$ correlation found on local early-type galaxies. Finally, the number density of our $z>4$ primary SMGs is found to be $1^{+0.9}_{-0.6}\times10^6$ cMpc$^{-3}$, suggesting that they can be the progenitors of $z\sim3-4$ massive quiescent galaxies. △ Less

Submitted 28 March, 2022; v1 submitted 14 December, 2021; originally announced December 2021.

Comments: 30 pages, 16 figures, ApJ in press

COLDz: Probing Cosmic Star Formation With Radio Free-free Emission

Authors: Hiddo S. B. Algera, Jacqueline A. Hodge, Dominik A. Riechers, Sarah K. Leslie, Ian Smail, Manuel Aravena, Elisabete da Cunha, Emanuele Daddi, Roberto Decarli, Mark Dickinson, Hansung B. Gim, Lucia Guaita, Benjamin Magnelli, Eric J. Murphy, Riccardo Pavesi, Mark T. Sargent, Chelsea E. Sharon, Jeff Wagg, Fabian Walter, Min Yun

Abstract: Radio free-free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum -- being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys -- the usage of free-free emission as a star formation rate tracer has mostly re… ▽ More Radio free-free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum -- being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys -- the usage of free-free emission as a star formation rate tracer has mostly remained limited to the local Universe. Here we perform a multi-frequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10 and 34 GHz in the COSMOS and GOODS-North fields to probe free-free emission in typical galaxies at the peak of cosmic star formation. We find that $z \sim 0.5 - 3$ star-forming galaxies exhibit radio emission at rest-frame frequencies of $\sim 65 - 90$ GHz that is $\sim 1.5 - 2\times$ fainter than would be expected from a simple combination of free-free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free-free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free-free emission at $0.5 \lesssim z \lesssim 3$, which are in good agreement with more established tracers at high redshift. In the future, deep multi-frequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free-free emission as a tracer of high-redshift star formation. △ Less

Submitted 1 November, 2021; originally announced November 2021.

Comments: Accepted for publication in ApJ; 22 pages + appendices, 11 figures in main text

An extreme case of galaxy and cluster co-evolution at $z$=0.7

Authors: Harald Ebeling, Johan Richard, Ian Smail, Alastair Edge, Anton Koekemoer, Lukas Zalesky

Abstract: We report the discovery of eMACSJ0252.4$-$2100 (eMACSJ0252), a massive and highly evolved galaxy cluster at $z=0.703$. Our analysis of Hubble Space Telescope imaging and VLT/MUSE and Keck/DEIMOS spectroscopy of the system finds a high velocity dispersion of 1020$^{+180}_{-190}$ km s$^{-1}$ and a high (if tentative) X-ray luminosity of $(1.2\pm 0.4)\times10^{45}$ erg s$^{-1}$ (0.1$-$2.4 keV). As ex… ▽ More We report the discovery of eMACSJ0252.4$-$2100 (eMACSJ0252), a massive and highly evolved galaxy cluster at $z=0.703$. Our analysis of Hubble Space Telescope imaging and VLT/MUSE and Keck/DEIMOS spectroscopy of the system finds a high velocity dispersion of 1020$^{+180}_{-190}$ km s$^{-1}$ and a high (if tentative) X-ray luminosity of $(1.2\pm 0.4)\times10^{45}$ erg s$^{-1}$ (0.1$-$2.4 keV). As extreme is the system's brightest cluster galaxy, a giant cD galaxy that forms stars at a rate of between 85 and 300 M$_\odot$ yr$^{-1}$ and features an extended halo of diffuse [OII] emission, as well as evidence of dust. Its most remarkable properties, however, are an exceptionally high ellipticity and a radially symmetric flow of gas in the surrounding intracluster medium, potential direct kinematic evidence of a cooling flow. A strong-lensing analysis, anchored by two multiple-image systems with spectroscopic redshifts, finds the best lens model to consist of a single cluster-scale halo with a total mass of $(1.9\pm0.1)\times 10^{14}$ M$_\odot$ within 250 kpc of the cluster core and, again, an extraordinarily high ellipticity of $e=0.8$. Although further, in-depth studies across the electromagnetic spectrum (especially in the X-ray regime) are needed to conclusively determine the dynamical state of the system, the properties established so far suggest that eMACSJ0252 must have already been highly evolved well before $z\sim 1$, making it a prime target to constrain the physical mechanisms and history of the co-evolution or dark-matter halos and baryons in the era of cluster formation. △ Less

Submitted 21 September, 2021; v1 submitted 17 September, 2021; originally announced September 2021.

Comments: 9 pages, 8 figures, accepted for publication in MNRAS

Extensive Lensing Survey of Optical and Near-Infrared Dark Objects (El Sonido): HST H-Faint Galaxies behind 101 Lensing Clusters

Authors: Fengwu Sun, Eiichi Egami, Pablo G. Pérez-González, Ian Smail, Karina I. Caputi, Franz E. Bauer, Timothy D. Rawle, Seiji Fujimoto, Kotaro Kohno, Ugnė Dudzevičiūtė, Hakim Atek, Matteo Bianconi, Scott C. Chapman, Francoise Combes, Mathilde Jauzac, Jean-Baptiste Jolly, Anton M. Koekemoer, Georgios E. Magdis, Giulia Rodighiero, Wiphu Rujopakarn, Daniel Schaerer, Charles L. Steinhardt, Paul Van der Werf, Gregory L. Walth, John R. Weaver

Abstract: We present a Spitzer/IRAC survey of H-faint ($H_{160} \gtrsim 26.4$, $<5σ$) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of $\sim$648 arcmin$^2$ (effectively $\sim$221 arcmin$^2$ in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 $\mathrm{μm}$; median CH2$=22.46\pm0.11$ AB mag) that lack robust HST/WFC3-IR F160W counte… ▽ More We present a Spitzer/IRAC survey of H-faint ($H_{160} \gtrsim 26.4$, $<5σ$) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of $\sim$648 arcmin$^2$ (effectively $\sim$221 arcmin$^2$ in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 $\mathrm{μm}$; median CH2$=22.46\pm0.11$ AB mag) that lack robust HST/WFC3-IR F160W counterparts. The most remarkable source in our sample, namely ES-009 in the field of Abell 2813, is the brightest H-faint galaxy at 4.5 $\mathrm{μm}$ known so far ($\mathrm{CH2}=20.48\pm0.03$ AB mag). We show that the H-faint sources in our sample are massive (median $M_\mathrm{star} = 10^{10.3\pm 0.3}$ $M_\odot$), star-forming (median star formation rate $=100_{-40}^{+60}$ $M_\odot$yr$^{-1}$) and dust-obscured ($A_V=2.6\pm0.3$) galaxies around a median photometric redshift of $z=3.9\pm0.4$. The stellar continua of 14 H-faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius ($R_\mathrm{e,circ}$; lensing corrected) of $1.9\pm0.2$ kpc and $<1.5$ kpc for the resolved and whole samples, respectively. This is consistent with the sizes of massive unobscured galaxies at $z\sim4$, indicating that H-faint galaxies represent the dusty tail of the distribution of a wider galaxy population. Comparing with the ALMA dust continuum sizes of similar galaxies reported previously, we conclude that the heavy dust obscuration in H-faint galaxies is related to the compactness of both stellar and dust continua ($R_\mathrm{e,circ}\sim 1$ kpc). These H-faint galaxies make up $16_{-7}^{+13}$% of the galaxies in the stellar mass range of $10^{10}-10^{11.2}$ $M_\odot$ at $z=3\sim5$, contributing to $8_{-4}^{+8}$% of the cosmic star formation rate density in this epoch and likely tracing the early phase of massive galaxy formation. △ Less

Submitted 8 September, 2021; v1 submitted 3 September, 2021; originally announced September 2021.

Comments: 26 pages, 10 figures, 3 tables. Accepted for publication in ApJ

Radio spectral properties of star-forming galaxies in the MIGHTEE-COSMOS field and their impact on the far-infrared-radio correlation

Authors: Fangxia An, M. Vaccari, Ian Smail, M. J. Jarvis, I. H. Whittam, C. L. Hale, S. Jin, J. D. Collier, E. Daddi, J. Delhaize, B. Frank, E. J. Murphy, M. Prescott, S. Sekhar, A. R. Taylor, Y. Ao, K. Knowles, L. Marchetti, S. M. Randriamampandry, Z. Randriamanakoto

Abstract: We study the radio spectral properties of 2,094 star-forming galaxies (SFGs) by combining our early science data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey with VLA, GMRT radio data, and rich ancillary data in the COSMOS field. These SFGs are selected at VLA 3GHz, and their flux densities from MeerKAT 1.3GHz and GMRT 325MHz imaging data are extracted using… ▽ More We study the radio spectral properties of 2,094 star-forming galaxies (SFGs) by combining our early science data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey with VLA, GMRT radio data, and rich ancillary data in the COSMOS field. These SFGs are selected at VLA 3GHz, and their flux densities from MeerKAT 1.3GHz and GMRT 325MHz imaging data are extracted using the "super-deblending" technique. The median radio spectral index is $α_{\rm 1.3GHz}^{\rm 3GHz}=-0.80\pm0.01$ without significant variation across the rest-frame frequencies ~1.3-10GHz, indicating radio spectra dominated by synchrotron radiation. On average, the radio spectrum at observer-frame 1.3-3GHz slightly steepens with increasing stellar mass with a linear fitted slope of $β=-0.08\pm0.01$, which could be explained by age-related synchrotron losses. Due to the sensitivity of GMRT 325MHz data, we apply a further flux density cut at 3GHz ($S_{\rm 3GHz}\ge50\,μ$Jy) and obtain a sample of 166 SFGs with measured flux densities at 325MHz, 1.3GHz, and 3GHz. On average, the radio spectrum of SFGs flattens at low frequency with the median spectral indices of $α^{\rm 1.3GHz}_{\rm 325MHz}=-0.59^{+0.02}_{-0.03}$ and $α^{\rm 3.0GHz}_{\rm 1.3GHz}=-0.74^{+0.01}_{-0.02}$. At low frequency, our stacking analyses show that the radio spectrum also slightly steepens with increasing stellar mass. By comparing the far-infrared-radio correlations of SFGs based on different radio spectral indices, we find that adopting $α_{\rm 1.3GHz}^{\rm 3GHz}$ for $k$-corrections will significantly underestimate the infrared-to-radio luminosity ratio ($q_{\rm IR}$) for >17% of the SFGs with measured flux density at the three radio frequencies in our sample, because their radio spectra are significantly flatter at low frequency (0.33-1.3GHz). △ Less

Submitted 5 August, 2021; originally announced August 2021.

Comments: 15 pages, 6 figures, 1 table; accepted for publication in MNRAS on 2021 Aug 4

ALMA Observations of Lyman-alpha Blob 1: Multiple major-mergers and widely distributed interstellar media

Authors: Hideki Umehata, Ian Smail, Charles C. Steidel, Matthew Hayes, Douglas Scott, A. M. Swinbank, R. J. Ivison, Toru Nagao, Mariko Kubo, Kouichiro Nakanishi, Yuichi Matsuda, Soh Ikarashi, Yoichi Tamura, J. E. Geach

Abstract: We present observations of a giant Lyman-alpha blob in the SSA22 proto-cluster at z=3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array (ALMA). Dust continuum, along with [C II]158um, and CO(4-3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ~100 kpc central region. Seven galaxies at z=3.0987-3.1016 in the surroundings are ide… ▽ More We present observations of a giant Lyman-alpha blob in the SSA22 proto-cluster at z=3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array (ALMA). Dust continuum, along with [C II]158um, and CO(4-3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ~100 kpc central region. Seven galaxies at z=3.0987-3.1016 in the surroundings are identified in [C II] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C II] and infrared luminosity ratios for the widely distributed media (L[C II]/LIR~0.01-0.001) suggest that the observed extended interstellar media are likely to have originated from star-formation activity and the contribution from shocked gas is probably not dominant. LAB1 is found to harbour a total molecular gas mass Mmol=(8.7+/-2.0)e+10 Msun, concentrated in the core region of the Ly-alpha-emitting area. While (primarily obscured) star-formation activity in the LAB1 core is one of the most plausible power sources for the Ly-alpha emission, multiple major-mergers found in the core may also play a role in making LAB1 exceptionally bright and extended in Ly-alpha as a result of cooling radiation induced by gravitational interactions. △ Less

Submitted 2 July, 2021; originally announced July 2021.

Comments: 23 pages, 11 figures, accepted for publication in ApJ

Measurements of the dust properties in z~1-3 SMGs with ALMA

Authors: E. da Cunha, J. A. Hodge, C. M. Casey, H. S. B. Algera, M. Kaasinen, I. Smail, F. Walter, W. N. Brandt, H. Dannerbauer, R. Decarli, B. A. Groves, K. K. Knudsen, A. M. Swinbank, A. Weiss, P. van der Werf, J. A. Zavala

Abstract: We present Atacama Large Millimetre Array (ALMA) 2mm continuum observations of a complete and unbiased sample of 99 870micron-selected sub-millimeter galaxies (SMGs) in the Extended Chandra Deep Field South (ALESS). Our observations of each SMG reach average sensitivities of 53 microJy/beam. We measure the flux densities for 70 sources, for which we obtain a typical 870micron-to-2mm flux ratio of… ▽ More We present Atacama Large Millimetre Array (ALMA) 2mm continuum observations of a complete and unbiased sample of 99 870micron-selected sub-millimeter galaxies (SMGs) in the Extended Chandra Deep Field South (ALESS). Our observations of each SMG reach average sensitivities of 53 microJy/beam. We measure the flux densities for 70 sources, for which we obtain a typical 870micron-to-2mm flux ratio of 14 +/- 5. We do not find a redshift dependence of this flux ratio, which would be expected if the dust emission properties of our SMGs were the same at all redshifts. By combining our ALMA measurements with existing Herschel/SPIRE observations, we construct a (biased) subset of 27 galaxies for which the cool dust emission is sufficiently well sampled to obtain precise constraints on their dust properties using simple isothermal models. Thanks to our new 2mm observations, the dust emissivity index is well-constrained and robust against different dust opacity assumptions. The median dust emissivity index of our SMGs is $β\simeq1.9\pm0.4$, consistent with the emissivity index of dust in the Milky Way and other local and high-redshift galaxies, as well as classical dust grain model predictions. We also find a negative correlation between the dust temperature and $β$, similar to low-redshift observational and theoretical studies. Our results indicate that $β\simeq2$ in high-redshift dusty star-forming galaxies, implying little evolution in dust grain properties between our SMGs and local dusty galaxy samples, and suggesting these high-mass and high-metallicity galaxies have dust reservoirs driven by grain growth in their ISM. △ Less

Submitted 16 June, 2021; originally announced June 2021.

Comments: 31 pages, 20 figures, accepted for publication in the Astrophysical Journal