Showing 1–50 of 209 results for author: Wilson, C D

MAUVE-MUSE: Ionization and Kinematic Signatures of Environmental Effects on Virgo Cluster Disks

Authors: Toby Brown, Luca Cortese, Barbara Catinella, A. Fraser-McKelvie, Adam B. Watts, Amirnezam Amiri, Alessandro Boselli, Woorak Choi, Aeree Chung, Timothy A. Davis, Eric Emsellem, Pavel Jáchym, María J. Jiménez-Donaire, Tutku Kolcu, Bumhyun Lee, Andrei Ristea, Jesse van de Sande, Kristine Spekkens, Sabine Thater, Christine D. Wilson, Nikki Zabel

Abstract: We present early science results from the MAUVE (Multiphase Astrophysics to Unveil the Virgo Environment) program which targets 40 Virgo Cluster galaxies to investigate the effect of environment on the interstellar medium (ISM) at ~100 pc scales. From 12 galaxies in the MAUVE-MUSE early sample, we find systematically elevated line ratios compared to PHANGS-MUSE field disks, with higher medians of… ▽ More We present early science results from the MAUVE (Multiphase Astrophysics to Unveil the Virgo Environment) program which targets 40 Virgo Cluster galaxies to investigate the effect of environment on the interstellar medium (ISM) at ~100 pc scales. From 12 galaxies in the MAUVE-MUSE early sample, we find systematically elevated line ratios compared to PHANGS-MUSE field disks, with higher medians of [N II]/H$α$ (0.75 vs. 0.50), [S II]/H$α$ (0.57 vs. 0.49), and [O III]/H$β$ (1.04 vs. 0.68). Spatially resolved BPT diagrams show 74% of MAUVE-MUSE spaxels ionized by sources other than H II regions, versus 61% in the field, and we find these ionization differences to be closely coupled to broadened kinematics. 44% of MAUVE-MUSE spaxels exceed H$α$ $σ_{LOS} = 40$ km/s (vs. 26% in the field), driven mainly by non-star-forming gas with $σ_{LOS}$ between 40 and 80 km/s, consistent with enhanced contribution of diffuse ionized gas (DIG). A subdominant tail of 5% of spaxels at $σ_{LOS} > 100$ km/s, largely absent in PHANGS-MUSE (1%), points to shocks or turbulent mixing layers from intracluster interactions. Our results show that environmental quenching primarily suppresses star formation, unveiling DIG as the dominant ionized component in cluster disks. The elevated line ratios and broadened kinematics observed in the MAUVE sample reflect the physical state of the ISM in the absence of vigorous star formation, rather than widespread direct environmental excitation. The observed shock-like emission provides an additional, secondary contribution likely driven by active interactions with the intracluster medium. △ Less

Submitted 21 April, 2026; originally announced April 2026.

Comments: 17 pages, 11 figures + appendices, accepted for publication in ApJ

Increased molecular gas velocity dispersion and star formation efficiency in barred galaxy centres

Authors: Jennifer M. Laing, Christine D. Wilson

Abstract: Work by the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) collaboration found higher molecular gas surface densities and velocity dispersions in the centres of barred galaxies compared to unbarred galaxies. We explore central molecular gas using published high resolution (150 pc) measurements of CO$(2-1)$ from the PHANGS-ALMA survey and a new velocity dispersion-dependent prescrip… ▽ More Work by the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) collaboration found higher molecular gas surface densities and velocity dispersions in the centres of barred galaxies compared to unbarred galaxies. We explore central molecular gas using published high resolution (150 pc) measurements of CO$(2-1)$ from the PHANGS-ALMA survey and a new velocity dispersion-dependent prescription for the CO-to-H$_{2}$ conversion factor $α_{\rm{CO}}$. Comparisons of the molecular gas surface density, velocity dispersion, star formation rate, and depletion time reveal that these quantities are different in the centres of barred and unbarred galaxies. Gas depletion times are found to be shorter in barred galaxy centres. Even when we control for the presence of an AGN, the velocity dispersion and depletion time are found to be statistically different between barred and unbarred galaxy centres. The higher velocity dispersion suggests extra non-circular motions, possibly due to the inflow of gas along the bar, that are not constant but must increase as the star formation rate increases. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 10 pages, plus 6 pages appendices, 3 figures, Accepted to AJ

VERTICO IX: Signatures of environmental processing of the gas in Virgo cluster spiral galaxies through mapping of CO isotopologues

Authors: Timothy A. Davis, Toby Brown, Maria J. Jimenez-Donaire, Christine D. Wilson, Dhruv Bisaria, Alessandro Boselli, Barbara Catinella, Aeree Chung, Luca Cortese, Sara Ellison, Bumhyun Lee, Ian D. Roberts, Kristine Spekkens, Vicente Villanueva, Nikki Zabel

Abstract: In this work we study CO isotopologue emission in the largest cluster galaxy sample to date: 48 VERTICO spiral galaxies in Virgo. We show for the first time in a significant sample that the physical conditions within the molecular gas appear to change as a galaxy's ISM is affected by environmental processes. 13CO is detected across the sample, both directly and via stacking, while C18O is detected… ▽ More In this work we study CO isotopologue emission in the largest cluster galaxy sample to date: 48 VERTICO spiral galaxies in Virgo. We show for the first time in a significant sample that the physical conditions within the molecular gas appear to change as a galaxy's ISM is affected by environmental processes. 13CO is detected across the sample, both directly and via stacking, while C18O is detected in a smaller number of systems. We use these data to study trends with global and radial galaxy properties. We show that the CO/13CO line ratio changes systematically with a variety of galaxy properties, including mean gas surface density, HI-deficiency and galaxy morphology. 13CO/C18O line ratios vary significantly, both radially and between galaxies, suggesting real variations in abundances are present. Such abundance changes may be due to star formation history differences, or speculatively even stellar initial mass function variations. We present a model where the optical depth of the molecular gas appears to change as a galaxy's ISM is affected by environmental processes. The molecular gas appears to become more transparent as the molecular medium is stripped, and then more opaque as the tightly bound remnant gas settles deep in the galaxy core. This explains the variations we see, and also helps explain similar observations in cluster early-type galaxies. Next generation simulations and dedicated observations of additional isotopologues could thus provide a powerful tool to help us understand the impact of environment on the ISM, and thus the quenching of galaxies. △ Less

Submitted 23 July, 2025; originally announced July 2025.

Comments: 12 pages, 11 figures, MNRAS accepted

Journal ref: Mon Not R Astron Soc (2025) 4031-4048

Building on the archives: Connecting the CN/CO intensity ratio with global galaxy properties in nearby U/LIRGs

Authors: Blake Ledger, Christine D. Wilson, Osvald Klimi, Nuria Torres-Alba, Toshiki Saito

Abstract: We use the CN/CO intensity ratio to obtain the dense gas fraction, $f_{\text{dense}}$, for a sample of 16 Ultra-luminous and Luminous Infrared Galaxies and compare $f_{\text{dense}}$ with a suite of global galaxy properties. We find a significant correlation between $f_{\text{dense}}$ and star formation rate calculated using both infrared luminosities and radio continuum, although there is signifi… ▽ More We use the CN/CO intensity ratio to obtain the dense gas fraction, $f_{\text{dense}}$, for a sample of 16 Ultra-luminous and Luminous Infrared Galaxies and compare $f_{\text{dense}}$ with a suite of global galaxy properties. We find a significant correlation between $f_{\text{dense}}$ and star formation rate calculated using both infrared luminosities and radio continuum, although there is significant scatter in each relation. We find no trend between global or peak $f_{\text{dense}}$ and merger stage. We find no correlation between global $f_{\text{dense}}$ and X-ray luminosity; however, the correlation becomes significant when we measure $f_{\text{dense}}$ at the location of peak X-ray emission. Our interpretation is that the dense gas is co-localized with strong X-ray emission from an active galactic nuclei or strong central star formation. △ Less

Submitted 4 February, 2025; originally announced February 2025.

Comments: Accepted to ApJ; 14 pages, 5 figures

Does the HCN/CO ratio trace the star-forming fraction of gas? II. Variations in CO and HCN Emissivity

Authors: Ashley R. Bemis, Christine D. Wilson, Piyush Sharda, Ian D. Roberts, Hao He

Abstract: We model emissivities of the HCN and CO $J=1-0$ transitions using measured properties of clouds found in normal star forming galaxies and more extreme systems. These models are compared with observations of HCN and CO $J=1-0$ transitions. We combine these model emissivities with predictions of gravoturbulent models of star formation, explore the impact of excitation and optical depth on CO and HCN… ▽ More We model emissivities of the HCN and CO $J=1-0$ transitions using measured properties of clouds found in normal star forming galaxies and more extreme systems. These models are compared with observations of HCN and CO $J=1-0$ transitions. We combine these model emissivities with predictions of gravoturbulent models of star formation, explore the impact of excitation and optical depth on CO and HCN emission, and assess if observed HCN/CO ratios track the fraction of gravitationally-bound dense gas, $f_\mathrm{grav}$, in molecular clouds. Our modeled HCN/CO ratios and emissivities are consistent with measurements from observations. CO emission shows a range of optical depths across different environments, from optically thick in normal galaxies to moderately optically thin in extreme systems. HCN is only moderately optically thick, with significant subthermal excitation in both normal and extreme galaxies. We find an anticorrelation between HCN/CO and $f_\mathrm{grav}$ as predicted by gravoturbulent models of star formation. Instead this ratio tracks gas at moderate densities ($n>10^{3.5}\ \mathrm{cm}^{-3}$), which is below the standard dense gas threshold of $n>10^{4.5}\ \mathrm{cm}^{-3}$. Variations in CO emissivity depend strongly on optical depth, due to variations in the dynamics of the cloud gas. HCN emissivity depends more strongly on excitation, and thus does not directly track variations in CO emissivity. We conclude that a single line ratio, such as HCN/CO, will not consistently track the fraction of gravitationally-bound, star-forming gas if the critical density for star formation varies in molecular clouds. This work highlights important uncertainties that need to be considered when observationally applying an HCN conversion factor in order to estimate the dense (i.e. $n>10^{4.5}\ \mathrm{cm}^{-3}$) gas content in nearby galaxies. △ Less

Submitted 24 January, 2025; v1 submitted 30 September, 2024; originally announced October 2024.

Comments: Accepted for publication in A&A

Journal ref: A&A 692, A146 (2024)

Cloud-Scale Molecular Gas Properties of the Antennae Merger: A Comparative Study with PHANGS-ALMA Galaxies and NGC 3256

Authors: Nathan Brunetti, Christine D. Wilson, Hao He, Jiayi Sun, Adam K. Leroy, Erik Rosolowsky, Ashley Bemis, Frank Bigiel, Brent Groves, Toshiki Saito, Eva Schinnerer

Abstract: We present observations of the central 9 kpc of the Antennae merger (NGC 4038/9) at 55 pc resolution in the CO 2-1 line obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We use a pixel-based analysis to compare the gas properties in the Antennae to those in 70 nearby spiral galaxies from the PHANGS-ALMA survey, as well as the merger and nearest luminous infrared galaxy NGC 325… ▽ More We present observations of the central 9 kpc of the Antennae merger (NGC 4038/9) at 55 pc resolution in the CO 2-1 line obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). We use a pixel-based analysis to compare the gas properties in the Antennae to those in 70 nearby spiral galaxies from the PHANGS-ALMA survey, as well as the merger and nearest luminous infrared galaxy NGC 3256. Compared to PHANGS galaxies at matched spatial resolution, the molecular gas in the Antennae exhibits some of the highest surface densities, velocity dispersions, peak brightness temperatures, and turbulent pressures. However, the virial parameters in the Antennae are consistent with many of the PHANGS galaxies. NGC 3256 has similar gas surface densities but higher nuclear velocity dispersions than the Antennae, as well as higher system-wide peak brightness temperatures and virial parameters. NGC 3256 is at a later stage in the merging process than the Antennae, which may result in more intense merger-driven gas flows that could drive up the turbulence in the gas. The high virial parameters in NGC 3256 may indicate that this increased turbulence is suppressing future star formation as NGC 3256 moves out of the starburst phase. In comparison, the relatively normal virial parameters in the Antennae may imply that it is about to undergo a new burst of star formation. △ Less

Submitted 6 April, 2024; originally announced April 2024.

Comments: 16 pages, 8 figures, accepted to MNRAS

Unraveling the Mystery of the Low CO-to-H$_2$ Conversion Factor in Starburst Galaxies: RADEX Modeling of the Antennae

Authors: Hao He, Christine D. Wilson, Jiayi Sun, Yu-Hsuan Teng, Erik Rosolowsky, Ashley R. Bemis

Abstract: CO emission has been widely used as a tracer of molecular gas mass. However, it is a long-standing issue to accurately constrain the CO-to-H$_2$ conversion factor ($α_{\mathrm{CO}}$) that converts CO luminosity to molecular gas mass, especially in starburst galaxies. We present the first resolved $α_{\mathrm{CO}}$ modeling results with multiple ALMA CO and $^{13}$CO transition observations at both… ▽ More CO emission has been widely used as a tracer of molecular gas mass. However, it is a long-standing issue to accurately constrain the CO-to-H$_2$ conversion factor ($α_{\mathrm{CO}}$) that converts CO luminosity to molecular gas mass, especially in starburst galaxies. We present the first resolved $α_{\mathrm{CO}}$ modeling results with multiple ALMA CO and $^{13}$CO transition observations at both giant molecular cloud (GMC) scale at 150 pc and kpc scale for one of the closest starburst mergers, the Antennae. By combining our CO modeling results and measurements of 350 GHz dust continuum, we find that most GMCs in the Antennae have $α_{\mathrm{CO}}$ values $\sim$4 times smaller than the commonly adopted Milky Way value (4.3). We find $α_{\mathrm{CO}}$ at GMC scales shows a strong dependence on CO intensity, $^{13}$CO/CO ratio and GMC velocity dispersion, which is consistent with various theoretical and simulation predictions. Specifically, we suggest that the $^{13}$CO/CO line ratio and the velocity dispersion can be used to infer $α_{\mathrm{CO}}$ in starburst regions. By applying our modeled $α_{\mathrm{CO}}$ in GMC analyses, we find that GMCs in the Antennae are less gravitationally bound than in normal spiral galaxies, which is more consistent with what is predicted by merger simulations. At kpc scale, we find that our modeled $α_{\mathrm{CO}}$ values are smaller than the modeled $α_{\mathrm{CO}}$ at GMC scale by 40%, which can be due to inclusion of a diffuse gas component with lower $α_{\mathrm{CO}}$ values. We find a similar correlation of $α_{\mathrm{CO}}$ and CO intensity at kpc scales to that at GMC scales. △ Less

Submitted 9 June, 2024; v1 submitted 29 January, 2024; originally announced January 2024.

Comments: 22 pages and 16 figures in the main text; accepted to ApJ

Hidden Gems on a Ring: Infant Massive Clusters and Their Formation Timeline Unveiled by ALMA, HST, and JWST in NGC 3351

Authors: Jiayi Sun, Hao He, Kyle Batschkun, Rebecca C. Levy, Kimberly Emig, M. Jimena Rodriguez, Hamid Hassani, Adam K. Leroy, Eva Schinnerer, Eve C. Ostriker, Christine D. Wilson, Alberto D. Bolatto, Elisabeth A. C. Mills, Erik Rosolowsky, Janice C. Lee, Daniel A. Dale, Kirsten L. Larson, David A. Thilker, Leonardo Ubeda, Bradley C. Whitmore, Thomas G. Williams, Ashley. T. Barnes, Frank Bigiel, Melanie Chevance, Simon C. O. Glover , et al. (16 additional authors not shown)

Abstract: We study young massive clusters (YMCs) in their embedded "infant" phase with $\sim0.\!^{\prime\prime}1$ ALMA, HST, and JWST observations targeting the central starburst ring in NGC 3351, a nearby Milky Way analog galaxy. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on… ▽ More We study young massive clusters (YMCs) in their embedded "infant" phase with $\sim0.\!^{\prime\prime}1$ ALMA, HST, and JWST observations targeting the central starburst ring in NGC 3351, a nearby Milky Way analog galaxy. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (${\sim}10^5\;\mathrm{M_\odot}$), small radii (${\lesssim}\,5\;\mathrm{pc}$), large escape velocities ($6{-}10\;\mathrm{km/s}$), and short free-fall times ($0.5{-}1\;\mathrm{Myr}$). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed HII region-cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline going from $\sim$1-2 Myr before cluster formation as starless clumps, to $\sim$4-6 Myr after as exposed HII region-cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit an non-uniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows. △ Less

Submitted 10 April, 2024; v1 submitted 25 January, 2024; originally announced January 2024.

Comments: 27 pages, 12 figures; ApJ accepted

Stored in the archives: Uncovering the CN/CO intensity ratio with ALMA in nearby U/LIRGs

Authors: Blake Ledger, Toshiki Saito, Daisuke Iono, Christine D. Wilson

Abstract: We present an archival Atacama Large Millimeter/submillimeter Array (ALMA) study of the CN N = 1 - 0 / CO J = 1 - 0 intensity ratio in nearby (z < 0.05) Ultra Luminous and Luminous Infrared Galaxies (U/LIRGs). We identify sixteen U/LIRGs that have been observed in both CN and CO lines at $\sim$ 500 pc resolution based on sixteen different ALMA projects. We measure the (CN bright)/CO and (CN bright… ▽ More We present an archival Atacama Large Millimeter/submillimeter Array (ALMA) study of the CN N = 1 - 0 / CO J = 1 - 0 intensity ratio in nearby (z < 0.05) Ultra Luminous and Luminous Infrared Galaxies (U/LIRGs). We identify sixteen U/LIRGs that have been observed in both CN and CO lines at $\sim$ 500 pc resolution based on sixteen different ALMA projects. We measure the (CN bright)/CO and (CN bright)/(CN faint) intensity ratios at an ensemble of molecular clouds scales (CN bright = CN N = 1 - 0, J = 3/2 - 1/2; CN faint = CN N = 1 - 0, J = 1/2 - 1/2 hyperfine groupings). Our global measured (CN bright)/CO ratios range from 0.02-0.15 in LIRGs and 0.08-0.17 in ULIRGs. We attribute the larger spread in LIRGs to the variety of galaxy environments included in our sample. Overall, we find that the (CN bright)/CO ratio is higher in nuclear regions, where the physical and excitation conditions favour increased CN emission relative to the disk regions. 10 out of 11 galaxies which contain well-documented active galactic nuclei show higher ratios in the nucleus compared to the disk. Finally, we measure the median resolved (CN bright)/(CN faint) ratio and use it to estimate the total integrated CN line optical depth in ULIRGs ($τ\sim$ 0.96) and LIRGs ($τ\sim$ 0.23). The optical depth difference is likely due to the higher molecular gas surface densities found in the more compact ULIRG systems. △ Less

Submitted 26 October, 2023; originally announced October 2023.

Comments: Accepted to MNRAS; 18 pages, 9 figures

VERTICO and IllustrisTNG: The spatially resolved effects of environment on galactic gas

Authors: Adam R. H. Stevens, Toby Brown, Benedikt Diemer, Annalisa Pillepich, Lars Hernquist, Dylan Nelson, Yannick M. Bahé, Alessandro Boselli, Timothy A. Davis, Pascal J. Elahi, Sara L. Ellison, María J. Jiménez-Donaire, Ian D. Roberts, Kristine Spekkens, Vicente Villanueva, Adam B. Watts, Christine D. Wilson, Nikki Zabel

Abstract: It has been shown in previous publications that the TNG100 simulation quantitatively reproduces the observed reduction in each of the total atomic and total molecular hydrogen gas for galaxies within massive halos, i.e.~dense environments. In this Letter, we study how well TNG50 reproduces the resolved effects of a Virgo-like cluster environment on the gas surface densities of satellite galaxies w… ▽ More It has been shown in previous publications that the TNG100 simulation quantitatively reproduces the observed reduction in each of the total atomic and total molecular hydrogen gas for galaxies within massive halos, i.e.~dense environments. In this Letter, we study how well TNG50 reproduces the resolved effects of a Virgo-like cluster environment on the gas surface densities of satellite galaxies with $m_* > \! 10^9\,{\rm M}_\odot$ and ${\rm SFR} \! > 0.05\,{\rm M}_\odot\,{\rm yr}^{-1}$. We select galaxies in the simulation that are analogous to those in the HERACLES and VERTICO surveys, and mock-observe them to the common specifications of the data. Although TNG50 does not quantitatively match the observed gas surface densities in the centers of galaxies, the simulation does qualitatively reproduce the trends of gas truncation and central density suppression seen in VERTICO in both HI and H$_2$. This result promises that modern cosmological hydrodynamic simulations can be used to reliably model the post-infall histories of cluster satellite galaxies. △ Less

Submitted 11 October, 2023; originally announced October 2023.

Comments: 9 pages, 4 figures, accepted in ApJL

VERTICO VII: Environmental quenching caused by suppression of molecular gas content and star formation efficiency in Virgo Cluster galaxies

Authors: Toby Brown, Ian D. Roberts, Mallory Thorp, Sara L. Ellison, Nikki Zabel, Christine D. Wilson, Yannick M. Bahé, Dhruv Bisaria, Alberto D. Bolatto, Alessandro Boselli, Aeree Chung, Luca Cortese, Barbara Catinella, Timothy A. Davis, María J. Jiménez-Donaire, Claudia D. P. Lagos, Bumhyun Lee, Laura C. Parker, Rory Smith, Kristine Spekkens, Adam R. H. Stevens, Vicente Villanueva, Adam B. Watts

Abstract: We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 parsec scales. We present the first resolved star-forming main sequence for cluster galaxies, dividing the sample based on their global HI properties and comparing to a control sample of field galaxies. HI-poor cluster galaxies have reduced star formation rate (SFR) surface densities with resp… ▽ More We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 parsec scales. We present the first resolved star-forming main sequence for cluster galaxies, dividing the sample based on their global HI properties and comparing to a control sample of field galaxies. HI-poor cluster galaxies have reduced star formation rate (SFR) surface densities with respect to both HI-normal cluster and field galaxies (0.5 dex), suggesting that mechanisms regulating the global HI content are responsible for quenching local star formation. We demonstrate that the observed quenching in HI-poor galaxies is caused by environmental processes such as ram pressure stripping (RPS) simultaneously reducing molecular gas surface density and star formation efficiency (SFE), compared to regions in HI-normal systems (by 0.38 and 0.22 dex, respectively). We observe systematically elevated SFRs that are driven by increased molecular gas surface densities at fixed stellar mass surface density in the outskirts of early-stage RPS galaxies, while SFE remains unchanged with respect to the field sample. We quantify how RPS and starvation affect the star formation cycle of inner and outer galaxy discs as they are processed by the cluster. We show both are effective quenching mechanisms with the key difference being that RPS acts upon the galaxy outskirts while starvation regulates the star formation cycle throughout disc, including within the truncation radius. For both processes, the quenching is caused by a simultaneous reduction in molecular gas surface densities and SFE at fixed stellar mass surface density. △ Less

Submitted 21 August, 2023; originally announced August 2023.

Comments: 17 pages, 1 table, 5 figures, accepted for publication in ApJ

VERTICO VI: Cold-gas asymmetries in Virgo cluster galaxies

Authors: Ian D. Roberts, Toby Brown, Nikki Zabel, Christine D. Wilson, Aeree Chung, Laura C. Parker, Dhruv Bisaria, Alessandro Boselli, Barbara Catinella, Ryan Chown, Luca Cortese, Timothy A. Davis, Sara Ellison, Maria Jesus Jimenez-Donaire, Bumhyun Lee, Rory Smith, Kristine Spekkens, Adam R. H. Stevens, Mallory Thorp, Vincente Villanueva, Adam B. Watts, Charlotte Welker, Hyein Yoon

Abstract: We analyze cold-gas distributions in Virgo cluster galaxies using resolved CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas (VIVA) surveys. From a theoretical perspective, it is expected that environmental processes in clusters will have a stronger influence on diffuse atomic gas compared to th… ▽ More We analyze cold-gas distributions in Virgo cluster galaxies using resolved CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas (VIVA) surveys. From a theoretical perspective, it is expected that environmental processes in clusters will have a stronger influence on diffuse atomic gas compared to the relatively dense molecular gas component, and that these environmental perturbations can compress the cold interstellar medium in cluster galaxies leading to elevated star formation. In this work we observationally test these predictions for star-forming satellite galaxies within the Virgo cluster. We divide our Virgo galaxy sample into HI-normal, HI-tailed, and HI-truncated classes and show, unsurprisingly, that the HI-tailed galaxies have the largest quantitative HI asymmetries. We also compare to a control sample of non-cluster galaxies and find that Virgo galaxies, on average, have HI asymmetries that are 40 +/- 10 per cent larger than the control. There is less separation between control, HI-normal, HI-tailed, and HI-truncated galaxies in terms of H2 asymmetries, and on average, Virgo galaxies have H2 asymmetries that are only marginally (20 +/- 10 per cent) larger than the control sample. We find a weak correlation between HI and H2 asymmetries over our entire sample, but a stronger correlation for those specific galaxies being strongly impacted by environmental perturbations. Finally, we divide the discs of the HI-tailed Virgo galaxies into a leading half and trailing half according to the observed tail direction. We find evidence for excess molecular gas mass on the leading halves of the disc. This excess molecular gas on the leading half is accompanied by an excess in star formation rate such that the depletion time is, on average, unchanged. △ Less

Submitted 24 May, 2023; originally announced May 2023.

Comments: 15 pages, 8 figures, 1 table, accepted for publication in A&A

Journal ref: A&A 675, A78 (2023)

VERTICO V: The environmentally driven evolution of the inner cold gas discs of Virgo cluster galaxies

Authors: Adam B. Watts, Luca Cortese, Barbara Catinella, Toby Brown, Christine D. Wilson, Nikki Zabel, Ian D. Roberts, Timothy A. Davis, Mallory Thorp, Aeree Chung, Adam R. H. Stevens, Sara L. Ellison, Kristine Spekkens, Laura C. Parker, Yannick M. Bahé, Vicente Villanueva, María Jiménez-Donaire, Dhruv Bisaria, Alessandro Boselli, Alberto D. Bolatto, Bumhyun Lee

Abstract: The quenching of cluster satellite galaxies is inextricably linked to the suppression of their cold interstellar medium (ISM) by environmental mechanisms. While the removal of neutral atomic hydrogen (HI) at large radii is well studied, how the environment impacts the remaining gas in the centres of galaxies, which are dominated by molecular gas, is less clear. Using new observations from the Virg… ▽ More The quenching of cluster satellite galaxies is inextricably linked to the suppression of their cold interstellar medium (ISM) by environmental mechanisms. While the removal of neutral atomic hydrogen (HI) at large radii is well studied, how the environment impacts the remaining gas in the centres of galaxies, which are dominated by molecular gas, is less clear. Using new observations from the Virgo Environment traced in CO survey (VERTICO) and archival HI data, we study the HI and molecular gas within the optical discs of Virgo cluster galaxies on 1.2-kpc scales with spatially resolved scaling relations between stellar ($Σ_{\star}$), HI ($Σ_\mathrm{HI}$), and molecular gas ($Σ_\mathrm{mol}$) surface densities. Adopting HI deficiency as a measure of environmental impact, we find evidence that, in addition to removing the HI at large radii, the cluster processes also lower the average $Σ_\mathrm{HI}$ of the remaining gas even in the central 1.2 kpc. The impact on molecular gas is comparatively weaker than on the HI, and we show that the lower $Σ_\mathrm{mol}$ gas is removed first. In the most HI-deficient galaxies, however, we find evidence that environmental processes reduce the typical $Σ_\mathrm{mol}$ of the remaining gas by nearly a factor of 3. We find no evidence for environment-driven elevation of $Σ_\mathrm{HI}$ or $Σ_\mathrm{mol}$ in HI-deficient galaxies. Using the ratio of $Σ_\mathrm{mol}$-to-$Σ_\mathrm{HI}$ in individual regions, we show that changes in the ISM physical conditions, estimated using the total gas surface density and midplane hydrostatic pressure, cannot explain the observed reduction in molecular gas content. Instead, we suggest that direct stripping of the molecular gas is required to explain our results. △ Less

Submitted 13 March, 2023; originally announced March 2023.

Comments: Accepted for publication in PASA. Main text is 19 pages including 12 figures and 3 tables, plus 1 appendix. A 2.5 min, high-level summary can be found at https://youtu.be/7djMmVEpDVc

A nearly constant CN/HCN line ratio in nearby galaxies: CN as a new tracer of dense gas

Authors: Christine D. Wilson, Ashley Bemis, Blake Ledger, Osvald Klimi

Abstract: We investigate the relationship between CN N = 1 - 0 and HCN J = 1 - 0 emission on scales from 30 pc to 400 pc using ALMA archival data, for which CN is often observed simultaneously with the CO J = 1 - 0 line. In a sample of 9 nearby galaxies ranging from ultra-luminous infrared galaxies to normal spiral galaxies, we measure a remarkably constant CN/HCN line intensity ratio of 0.86 $\pm$ 0.07 (st… ▽ More We investigate the relationship between CN N = 1 - 0 and HCN J = 1 - 0 emission on scales from 30 pc to 400 pc using ALMA archival data, for which CN is often observed simultaneously with the CO J = 1 - 0 line. In a sample of 9 nearby galaxies ranging from ultra-luminous infrared galaxies to normal spiral galaxies, we measure a remarkably constant CN/HCN line intensity ratio of 0.86 $\pm$ 0.07 (standard deviation of 0.20). This relatively constant CN/HCN line ratio is rather unexpected, as models of photon dominated regions have suggested that HCN emission traces shielded regions with high column densities while CN should trace dense gas exposed to high ultraviolet radiation fields. We find that the CN/HCN line ratio shows no significant correlation with molecular gas surface density, but shows a mild trend (increase of ~ 1.3 per dex) with both star formation rate surface density and star formation efficiency (the inverse of the molecular gas depletion time). Some starburst and active galactic nuclei show small enhancements in their CN/HCN ratio, while other nuclei show no significant difference from their surrounding disks. The nearly constant CN/HCN line ratio implies that CN, like HCN, can be used as a tracer of dense gas mass and dense gas fraction in nearby galaxies. △ Less

Submitted 7 March, 2023; originally announced March 2023.

Comments: Accepted to MNRAS; 21 pages, 12 figures

The JCMT Nearby Galaxies Legacy Survey: SCUBA-2 observations of nearby galaxies

Authors: Kate Pattle, Walter Gear, Christine D. Wilson

Abstract: We present 850$μ$m observations of a sample of 8 nearby spiral galaxies, made using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT Nearby Galaxies Legacy Survey (NGLS). We corrected our data for the presence of the $^{12}$CO $J=3\to 2$ line in the SCUBA-2 850$μ$m bandwidth using NGLS HARP data, finding a typical $^{12}$CO contribution of $\sim 20$%. We measured… ▽ More We present 850$μ$m observations of a sample of 8 nearby spiral galaxies, made using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT Nearby Galaxies Legacy Survey (NGLS). We corrected our data for the presence of the $^{12}$CO $J=3\to 2$ line in the SCUBA-2 850$μ$m bandwidth using NGLS HARP data, finding a typical $^{12}$CO contribution of $\sim 20$%. We measured dust column densities, temperatures and opacity indices by fitting spectral energy distributions constructed from SCUBA-2 and archival Herschel observations, and used archival GALEX and Spitzer data to make maps of surface density of star formation ($Σ_{\rm SFR}$). Typically, comparing SCUBA-2-derived H$_2$ surface densities ($Σ_{\rm H_2}$) to $Σ_{\rm SFR}$ gives shallow star formation law indices within galaxies, with SCUBA-2-derived values typically being sublinear and Herschel-derived values typically being broadly linear. This difference is likely due to the effects of atmospheric filtering on the SCUBA-2 data. Comparing the mean values of $Σ_{\rm H_2}$ and $Σ_{\rm SFR}$ of the galaxies in our sample returns a steeper star formation law index, broadly consistent with both the Kennicutt-Schmidt value of 1.4 and linearity. Our results show that a SCUBA-2 detection is a good predictor of star formation. We suggest that Herschel emission traces gas in regions which will form stars on timescales $\sim 5-100$ Myr, comparable to the star formation timescale traced by GALEX and Spitzer data, while SCUBA-2 preferentially traces the densest gas within these regions, which likely forms stars on shorter timescales. △ Less

Submitted 28 February, 2023; originally announced February 2023.

Comments: Accepted for publication in MNRAS. 15 pages, 12 figures, 8 tables (plus 15 pages of appendices, with 31 figures)

Star Formation Laws and Efficiencies across 80 Nearby Galaxies

Authors: Jiayi Sun, Adam K. Leroy, Eve C. Ostriker, Sharon Meidt, Erik Rosolowsky, Eva Schinnerer, Christine D. Wilson, Dyas Utomo, Francesco Belfiore, Guillermo A. Blanc, Eric Emsellem, Christopher Faesi, Brent Groves, Annie Hughes, Eric W. Koch, Kathryn Kreckel, Daizhong Liu, Hsi-An Pan, Jerome Pety, Miguel Querejeta, Alessandro Razza, Toshiki Saito, Amy Sardone, Antonio Usero, Thomas G. Williams , et al. (15 additional authors not shown)

Abstract: We measure empirical relationships between the local star formation rate (SFR) and properties of the star-forming molecular gas on 1.5 kpc scales across 80 nearby galaxies. These relationships, commonly referred to as "star formation laws," aim at predicting the local SFR surface density from various combinations of molecular gas surface density, galactic orbital time, molecular cloud free-fall ti… ▽ More We measure empirical relationships between the local star formation rate (SFR) and properties of the star-forming molecular gas on 1.5 kpc scales across 80 nearby galaxies. These relationships, commonly referred to as "star formation laws," aim at predicting the local SFR surface density from various combinations of molecular gas surface density, galactic orbital time, molecular cloud free-fall time, and the interstellar medium dynamical equilibrium pressure. Leveraging a multiwavelength database built for the PHANGS survey, we measure these quantities consistently across all galaxies and quantify systematic uncertainties stemming from choices of SFR calibrations and the CO-to-H$_2$ conversion factors. The star formation laws we examine show 0.3-0.4 dex of intrinsic scatter, among which the molecular Kennicutt-Schmidt relation shows a $\sim$10% larger scatter than the other three. The slope of this relation ranges $β\approx0.9{-}1.2$, implying that the molecular gas depletion time remains roughly constant across the environments probed in our sample. The other relations have shallower slopes ($β\approx0.6{-}1.0$), suggesting that the star formation efficiency (SFE) per orbital time, the SFE per free-fall time, and the pressure-to-SFR surface density ratio (i.e., the feedback yield) may vary systematically with local molecular gas and SFR surface densities. Last but not least, the shapes of the star formation laws depend sensitively on methodological choices. Different choices of SFR calibrations can introduce systematic uncertainties of at least 10-15% in the star formation law slopes and 0.15-0.25 dex in their normalization, while the CO-to-H$_2$ conversion factors can additionally produce uncertainties of 20-25% for the slope and 0.10-0.20 dex for the normalization. △ Less

Submitted 23 February, 2023; originally announced February 2023.

Comments: 10 pages main text + 2 appendices. ApJL in press. Data products available at https://www.canfar.net/storage/list/phangs/RELEASES/Sun_etal_2023 . Slides summarizing key results can be found at https://www.dropbox.com/s/5gsegexeo9n0t05/Sun_et_PHANGS_2023.pptx?dl=0

Journal ref: ApJL, 945, L19 (2023)

Does the HCN/CO ratio trace the star-forming fraction of gas? I. A comparison with analytical models of star formation

Authors: Ashley R. Bemis, Christine D. Wilson

Abstract: We use archival ALMA observations of the HCN and CO $J=1-0$ transitions, in addition to the radio continuum at 93 GHz, to assess the relationship between dense gas, star formation, and gas dynamics in ten, nearby (U)LIRGs and late-type galaxy centers. We frame our results in the context of turbulent and gravoturbulent models of star formation to assess if the HCN/CO ratio tracks the gravitationall… ▽ More We use archival ALMA observations of the HCN and CO $J=1-0$ transitions, in addition to the radio continuum at 93 GHz, to assess the relationship between dense gas, star formation, and gas dynamics in ten, nearby (U)LIRGs and late-type galaxy centers. We frame our results in the context of turbulent and gravoturbulent models of star formation to assess if the HCN/CO ratio tracks the gravitationally-bound, star-forming gas in molecular clouds ($f_\mathrm{grav}$) at sub-kpc scales in nearby galaxies. We confirm that the HCN/CO ratio is a tracer of gas above $n_\mathrm{SF}\approx10^{4.5}$ cm$^{-3}$, but the sub-kpc variations in HCN/CO do not universally track $f_\mathrm{grav}$. We find strong evidence for the use of varying star formation density threshold models, which are able to reproduce trends observed in $t_\mathrm{dep}$ and $ε_\mathrm{ff}$ that fixed threshold models cannot. Composite lognormal and powerlaw models outperform pure lognormal models in reproducing the observed trends, even when using a fixed powerlaw slope. The ability of the composite models to better reproduce star formation properties of the gas provides additional indirect evidence that the star formation efficiency per free-fall time is proportional to the fraction of gravitationally-bound gas. △ Less

Submitted 16 January, 2023; originally announced January 2023.

Comments: 23 pages, 11 figures, 1 appendix, accepted for publication in ApJ

PHANGS-JWST First Results: A Global and Moderately Resolved View of Mid-Infrared and CO Line Emission from Galaxies at the Start of the JWST Era

Authors: Adam K. Leroy, Alberto D. Bolatto, Karin Sandstrom, Erik Rosolowsky, Ashley. T. Barnes, F. Bigiel, Médéric Boquien, Jakob S. den Brok, Yixian Cao, Jérémy Chastenet, Mélanie Chevance, I-Da Chiang, Ryan Chown, Dario Colombo, Sara L. Ellison, Eric Emsellem, Kathryn Grasha, Jonathan D. Henshaw, Annie Hughes, Ralf S. Klessen, Eric W. Koch, Jaeyeon Kim, Kathryn Kreckel, J. M. Diederik Kruijssen, Kirsten L. Larson , et al. (19 additional authors not shown)

Abstract: We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately ($\sim 1$ kpc) spatially resolved measurements of CO (1-0) and CO (2-1) intensity, $I_{\rm CO}$, and mid-IR intensity, $I_{\rm MIR}$, at 8, 12, 22, and 24$μ$m.… ▽ More We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately ($\sim 1$ kpc) spatially resolved measurements of CO (1-0) and CO (2-1) intensity, $I_{\rm CO}$, and mid-IR intensity, $I_{\rm MIR}$, at 8, 12, 22, and 24$μ$m. The $I_{\rm CO}$ vs. $I_{\rm MIR}$ relationship is reasonably described by a power law with slopes $0.7{-}1.2$ and normalization $I_{\rm CO} \sim 1$ K km s$^{-1}$ at $I_{\rm MIR} \sim 1$ MJy sr$^{-1}$. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO~(1-0) and CO (2-1) allow us to infer that $R_{21} \propto I_{\rm MIR}^{0.2}$, in good agreement with other work. The $8μ$m and $12μ$m bands, with strong PAH features, show steeper CO vs. mid-IR slopes than the $22μ$m and $24μ$m, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass ($M_\star$) and anti-correlates with SFR/$M_\star$. At $\sim 1$ kpc resolution, the first four PHANGS-JWST targets show CO to mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities. △ Less

Submitted 27 December, 2022; v1 submitted 19 December, 2022; originally announced December 2022.

Comments: 29 pages, 13 figures, key quantitative results in Table 3, Accepted as part of a PHANGS-JWST Focus Issue to appear in ApJ

VERTICO III: The Kennicutt-Schmidt relation in Virgo cluster galaxies

Authors: M. J. Jiménez-Donaire, T. Brown, C. D. Wilson, I. D. Roberts, N. Zabel, S. L. Ellison, M. Thorp, V. Villanueva, R. Chown, D. Bisaria, A. D. Bolatto, A. Boselli, B. Catinella, A. Chung, L. Cortese, T. A. Davis, C. D. P. Lagos, B. Lee, L. C. Parker, K. Spekkens, A. R. H. Stevens, J. Sun

Abstract: In this VERTICO science paper we aim to study how the star formation process depends on galactic environment and gravitational interactions in the context of galaxy evolution. We explore the scaling relation between the star formation rate (SFR) surface density and the molecular gas surface density, also known as the Kennicutt-Schmidt (KS) relation, in a subsample of Virgo cluster spiral galaxies.… ▽ More In this VERTICO science paper we aim to study how the star formation process depends on galactic environment and gravitational interactions in the context of galaxy evolution. We explore the scaling relation between the star formation rate (SFR) surface density and the molecular gas surface density, also known as the Kennicutt-Schmidt (KS) relation, in a subsample of Virgo cluster spiral galaxies. We use new ACA and TP observations from the VERTICO-ALMA Large Program at 720pc resolution to resolve the molecular gas content, as traced by the 12CO(2-1) transition, across the disks of 37 spiral galaxies in the Virgo cluster. In combination with archival observations, we estimate the parameters of the KS relation for the entire ensemble of galaxies, and within individual galaxies. We find the KS slope for the entire population to be N=0.97+/-0.07, with a characteristic molecular gas depletion time of 1.86Gyr for our full sample, in agreement with previous work in isolated star-forming galaxies. In individual galaxies, we find KS slopes ranging between 0.69 and 1.40, and typical star formation efficiencies (SFE) that can vary from galaxy to galaxy by a factor of ~4. These galaxy-to-galaxy variations account for ~0.20dex in scatter in the ensemble KS relation, which is characterized by a 0.42dex scatter. We find that the HI-deficient galaxies in the Virgo cluster show a steeper resolved KS relation and lower molecular gas efficiencies than HI-normal cluster galaxies. While the molecular gas content in Virgo cluster galaxies appears to behave similarly to that in isolated galaxies, our VERTICO sample shows that cluster environments play a key role in regulating star formation. The environmental mechanisms affecting the HI galaxy content also have a direct impact in the SFE of molecular gas in cluster galaxies, leading to longer depletion times in HI-deficient members. △ Less

Submitted 29 November, 2022; originally announced November 2022.

Comments: Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 671, A3 (2023)

VERTICO IV: Environmental Effects on the Gas Distribution and Star Formation Efficiency of Virgo Cluster Spirals

Authors: Vicente Villanueva, Alberto D. Bolatto, Stuart Vogel, Tobias Brown, Christine D. Wilson, Nikki Zabel, Sara Ellison, Adam R. H. Stevens, Maria Jesus Jimenez Donaire, Kristine Spekkens, Mallory Thorp, Timothy A. Davis, Laura C. Parker, Ian D. Roberts, Dhruv Bisaria, Alessandro Boselli, Barbara Catinella, Aeree Chung, Luca Cortese, Bumhyun Lee, Adam Watts

Abstract: We measure the molecular-to-atomic gas ratio, $R_{\rm mol}$, and the star formation rate (SFR) per unit molecular gas mass, SFE$_{\rm mol}$, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We determine their scale-lengths for the molecular and stellar components and find a roughly 3:5 ratio between them compared to $\sim$1:1 in field galaxies, indicating th… ▽ More We measure the molecular-to-atomic gas ratio, $R_{\rm mol}$, and the star formation rate (SFR) per unit molecular gas mass, SFE$_{\rm mol}$, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We determine their scale-lengths for the molecular and stellar components and find a roughly 3:5 ratio between them compared to $\sim$1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We compute $R_{\rm mol}$ as a function of different physical quantities. While the spatially-resolved $R_{\rm mol}$ on average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radius $R_{\rm e}$, $R_{\rm mol}(r<R_{\rm e})$, shows a systematic increase with the level of H$_{\rm I}$, truncation and/or asymmetry (H$_{\rm I}$ perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within $R_{\rm e}$, $R^{\rm mol}_{\star}(r<R_{\rm e})$ and $R^{\rm atom}_{\star}(r<R_{\rm e})$, shows that VERTICO galaxies have increasingly lower $R^{\rm atom}_{\star}(r<R_{\rm e})$ for larger levels of H$_{\rm I}$perturbation (compared to field galaxies matched in stellar mass), but no significant change in $R^{\rm mol}_{\star}(r<R_{\rm e})$. We also measure a clear systematic decrease of the SFE$_{\rm mol}$ within $R_{\rm e}$, SFE$_{\rm mol}(r<R_{\rm e})$, with increasingly perturbed H$_{\rm I}$. Therefore, compared to galaxies from the field, VERTICO galaxies are more compact in CO emission in relation to their stellar distribution, but increasingly perturbed atomic gas increases their $R_{\rm mol}$ and decreases the efficiency with which their molecular gas forms stars. (abridged) △ Less

Submitted 1 November, 2022; v1 submitted 11 October, 2022; originally announced October 2022.

The cold gas and dust properties of red star-forming galaxies

Authors: Ryan Chown, Laura C. Parker, Christine D. Wilson, Toby Brown, Fraser A. Evans, Yang Gao, Ho Seong Hwang, Lihwai Lin, Amelie Saintonge, Mark Sargent, Matthew W. L. Smith, Ting Xiao

Abstract: We study the cold gas and dust properties for a sample of red star forming galaxies called "red misfits." We collect single-dish CO observations and HI observations from representative samples of low-redshift galaxies, as well as our own JCMT CO observations of red misfits. We also obtain SCUBA-2 850 um observations for a subset of these galaxies. With these data we compare the molecular gas, tota… ▽ More We study the cold gas and dust properties for a sample of red star forming galaxies called "red misfits." We collect single-dish CO observations and HI observations from representative samples of low-redshift galaxies, as well as our own JCMT CO observations of red misfits. We also obtain SCUBA-2 850 um observations for a subset of these galaxies. With these data we compare the molecular gas, total cold gas, and dust properties of red misfits against those of their blue counterparts ("blue actives") taking non-detections into account using a survival analysis technique. We compare these properties at fixed position in the log SFR-log M* plane, as well as versus offset from the star-forming main sequence. Compared to blue actives, red misfits have slightly longer molecular gas depletion times, similar total gas depletion times, significantly lower molecular- and total-gas mass fractions, lower dust-to-stellar mass ratios, similar dust-to-gas ratios, and a significantly flatter slope in the $\log M_\mathrm{mol}$-$\log M_\star$ plane. Our results suggest that red misfits as a population are likely quenching due to a shortage in gas supply. △ Less

Submitted 24 August, 2022; v1 submitted 7 August, 2022; originally announced August 2022.

Comments: 16 pages, 7 Figures, accepted to MNRAS

Extreme giant molecular clouds in the luminous infrared galaxy NGC 3256

Authors: Nathan Brunetti, Christine D. Wilson

Abstract: (Abridged) We present a cloud decomposition of $^{12}$CO (2--1) observations of the merger and nearest luminous infrared galaxy, NGC 3256. 185 spatially and spectrally resolved clouds are identified across the central $\approx$ 130 kpc$^{2}$ at 90 pc resolution and completeness is estimated. We compare our cloud catalogue from NGC 3256 to ten galaxies observed in the PHANGS-ALMA survey. Distributi… ▽ More (Abridged) We present a cloud decomposition of $^{12}$CO (2--1) observations of the merger and nearest luminous infrared galaxy, NGC 3256. 185 spatially and spectrally resolved clouds are identified across the central $\approx$ 130 kpc$^{2}$ at 90 pc resolution and completeness is estimated. We compare our cloud catalogue from NGC 3256 to ten galaxies observed in the PHANGS-ALMA survey. Distributions in NGC 3256 of cloud velocity dispersions, luminosities, CO-estimated masses, mass surface densities, virial masses, virial parameters, size-linewidth coefficients, and internal turbulent pressures are significantly higher than in the PHANGS-ALMA galaxies. Cloud radii are slightly larger in NGC 3256 and free-fall times are shorter. The distribution of cloud eccentricities in NGC 3256 is indistinguishable from many PHANGS-ALMA galaxies, possibly because the dynamical state of clouds in NGC 3256 is similar to that of nearby spiral galaxies. However, the narrower distribution of virial parameters in NGC 3256 may reflect a narrower range of dynamical states than in PHANGS-ALMA galaxies. No clear picture of cloud alignment is detected, despite the large eccentricities. Correlations between cloud properties point to high external pressures in NGC 3256 keeping clouds bound and collapsing given such high velocity dispersions and star-formation rates. A fit to the cloud mass function gives a high-mass power-law slope of $-2.75^{+0.07}_{-0.01}$, near the average from PHANGS-ALMA galaxies. We also compare our results to a pixel-based analysis of these observations and find molecular-gas properties agree qualitatively, though peak brightness temperatures are somewhat higher and virial parameters and free-fall times are somewhat lower in this cloud-based analysis. △ Less

Submitted 11 July, 2022; originally announced July 2022.

Comments: accepted to MNRAS; 25 pages, 17 figures

On the scale-height of the molecular gas disc in Milky Way-like galaxies

Authors: Sarah M. R. Jeffreson, Jiayi Sun, Christine D. Wilson

Abstract: We study the relationship between the scale-height of the molecular gas disc and the turbulent velocity dispersion of the molecular interstellar medium within a simulation of a Milky Way-like galaxy in the moving-mesh code Arepo. We find that the vertical distribution of molecular gas can be described by a Gaussian function with a uniform scale-height of ~50 pc. We investigate whether this scale-h… ▽ More We study the relationship between the scale-height of the molecular gas disc and the turbulent velocity dispersion of the molecular interstellar medium within a simulation of a Milky Way-like galaxy in the moving-mesh code Arepo. We find that the vertical distribution of molecular gas can be described by a Gaussian function with a uniform scale-height of ~50 pc. We investigate whether this scale-height is consistent with a state of hydrostatic balance between gravity and turbulent pressure. We find that the hydrostatic prediction using the total turbulent velocity dispersion (as one would measure from kpc-scale observations) gives an over-estimate of the true molecular disc scale-height. The hydrostatic prediction using the velocity dispersion between the centroids of discrete giant molecular clouds (cloud-cloud velocity dispersion) leads to more-accurate estimates. The velocity dispersion internal to molecular clouds is elevated by the locally-enhanced gravitational field. Our results suggest that observations of molecular gas need to reach the scale of individual molecular clouds in order to accurately determine the molecular disc scale-height. △ Less

Submitted 29 June, 2022; originally announced June 2022.

Comments: MNRAS accepted, comments welcome. 14 pages, 10 figures

VERTICO II: effects of HI-identified environmental mechanisms on molecular gas

Authors: Nikki Zabel, Toby Brown, Christine D. Wilson, Timothy A. Davis, Luca Cortese, Laura C. Parker, Alessandro Boselli, Barbara Catinella, Ryan Chown, Aeree Chung, Tirna Deb, Sara L. Ellison, María J. Jiménez-Donaire, Bumhyun Lee, Ian D. Roberts, Kristine Spekkens, Adam R. H. Stevens, Mallory Thorp, Stephanie Tonnesen, Vicente Villanueva

Abstract: In this VERTICO early science paper we explore in detail how environmental mechanisms, identified in HI, affect the resolved properties of molecular gas reservoirs in cluster galaxies. The molecular gas is probed using ALMA ACA (+TP) observations of 12CO(2-1) in 51 spiral galaxies in the Virgo cluster (of which 49 are detected), all of which are included in the VIVA HI survey. The sample spans a s… ▽ More In this VERTICO early science paper we explore in detail how environmental mechanisms, identified in HI, affect the resolved properties of molecular gas reservoirs in cluster galaxies. The molecular gas is probed using ALMA ACA (+TP) observations of 12CO(2-1) in 51 spiral galaxies in the Virgo cluster (of which 49 are detected), all of which are included in the VIVA HI survey. The sample spans a stellar mass range of 9 < log M*/Msol < 11. We study molecular gas radial profiles, isodensity radii, and surface densities as a function of galaxy HI deficiency and morphology. There is a weak correlation between global HI and H2 deficiencies, and resolved properties of molecular gas correlate with HI deficiency: galaxies that have large HI deficiencies have relatively steep and truncated molecular gas radial profiles, which is due to the removal of low-surface density molecular gas on the outskirts. Therefore, while the environmental mechanisms observed in HI also affect molecular gas reservoirs, there is only a moderate reduction of the total amount of molecular gas. △ Less

Submitted 12 January, 2023; v1 submitted 11 May, 2022; originally announced May 2022.

Comments: Published in ApJ. 22 pages, 6 figures, 1 table, 1 appendix. Erratum accepted for publication in ApJ

VERTICO: The Virgo Environment Traced In CO Survey

Authors: Toby Brown, Christine D. Wilson, Nikki Zabel, Timothy A. Davis, Alessandro Boselli, Aeree Chung, Sara L. Ellison, Claudia D. P. Lagos, Adam R. H. Stevens, Luca Cortese, Yannick M. Bahé, Dhruv Bisaria, Alberto D. Bolatto, Claire R. Cashmore, Barbara Catinella, Ryan Chown, Benedikt Diemer, Pascal J. Elahi, Maan H. Hani, María J. Jiménez-Donaire, Bumhyun Lee, Katya Leidig, Angus Mok, Karen Pardos Olsen, Laura C. Parker , et al. (11 additional authors not shown)

Abstract: We present the Virgo Environment Traced in CO (VERTICO) survey, a new effort to map $^{12}$CO($2-1$), $^{13}$CO($2-1$), and C$^{18}$O($2-1$) in 51 Virgo Cluster galaxies with the Atacama Compact Array, part of the Atacama Large Millimeter/submillimeter Array (ALMA). The primary motivation of VERTICO is to understand the physical mechanisms that perturb molecular gas disks, and therefore star forma… ▽ More We present the Virgo Environment Traced in CO (VERTICO) survey, a new effort to map $^{12}$CO($2-1$), $^{13}$CO($2-1$), and C$^{18}$O($2-1$) in 51 Virgo Cluster galaxies with the Atacama Compact Array, part of the Atacama Large Millimeter/submillimeter Array (ALMA). The primary motivation of VERTICO is to understand the physical mechanisms that perturb molecular gas disks, and therefore star formation and galaxy evolution, in dense environments. This first paper contains an overview of VERTICO's design and sample selection, $^{12}$CO($2-1$) observations, and data reduction procedures. We characterize global $^{12}$CO($2-1$) fluxes and molecular gas masses for the 49 detected VERTICO galaxies, provide upper limits for the two non-detections, and produce resolved $^{12}$CO($2-1$) data products (median resolution $= 8^{\prime\prime} \approx 640~{\rm pc}$). Azimuthally averaged $^{12}$CO($2-1$) radial intensity profiles are presented along with derived molecular gas radii. We demonstrate the scientific power of VERTICO by comparing the molecular gas size--mass scaling relation for our galaxies with a control sample of field galaxies, highlighting the strong effect that radius definition has on this correlation. We discuss the drivers of the form and scatter in the size--mass relation and highlight areas for future work. VERTICO is an ideal resource for studying the fate of molecular gas in cluster galaxies and the physics of environment-driven processes that perturb the star formation cycle. Upon public release, the survey will provide a homogeneous legacy dataset for studying galaxy evolution in our closest cluster. △ Less

Submitted 1 November, 2021; originally announced November 2021.

Comments: 68 pages, 13 Figures, 2 Figure Sets, Accepted for publication in ApJS, Online FITS versions of Tables 1, 2, and 3 are available with the journal publication

The HASHTAG project: The First Submillimeter Images of the Andromeda Galaxy from the Ground

Authors: Matthew W. L. Smith, Stephen A. Eales, Thomas G. Williams, Bumhyun Lee, Zongnan Li, Pauline Barmby, Martin Bureau, Scott Chapman, Brian S. Cho, Aeree Chung, Eun Jung Chung, Hui-Hsuan Chung, Christopher J. R. Clark, David L. Clements, Timothy A. Davis, Ilse De Looze, David J. Eden, Gayathri Athikkat-Eknath, George P. Ford, Yu Gao, Walter Gear, Haley L. Gomez, Richard de Grijs, Jinhua He, Luis C. Ho , et al. (24 additional authors not shown)

Abstract: Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome by-product of also removing… ▽ More Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome by-product of also removing the galaxy's large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and present the first HASHTAG images of Andromeda at 450 and 850um. We also have created a method to predict the CO(J=3-2) line flux across M31, which contaminates the 850um band. We find that while normally the contamination is below our sensitivity limit, the contamination can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed. △ Less

Submitted 30 September, 2021; originally announced October 2021.

Comments: 26 pages, 19 figures. Submitted to ApJS June 2021, Accepted September 2021

Observed CN and HCN intensity ratios exhibit subtle variations in extreme galaxy environments

Authors: B. Ledger, C. D. Wilson, T. Michiyama, D. Iono, S. Aalto, T. Saito, A. Bemis, R. Aladro

Abstract: We use both new and archival ALMA data of three energy lines each of CN and HCN to explore intensity ratios in dense gas in NGC 3256, NGC 7469, and IRAS 13120-5453. The HCN (3-2)/HCN (1-0) intensity ratio varies in NGC 3256 and NGC 7469, with superlinear trends of 1.53$\pm$0.07 and 1.55$\pm$0.05, respectively. We find an offset to higher HCN (3-2)/HCN (1-0) intensity ratios (~0.8) in IRAS 13120-54… ▽ More We use both new and archival ALMA data of three energy lines each of CN and HCN to explore intensity ratios in dense gas in NGC 3256, NGC 7469, and IRAS 13120-5453. The HCN (3-2)/HCN (1-0) intensity ratio varies in NGC 3256 and NGC 7469, with superlinear trends of 1.53$\pm$0.07 and 1.55$\pm$0.05, respectively. We find an offset to higher HCN (3-2)/HCN (1-0) intensity ratios (~0.8) in IRAS 13120-5453 compared to NGC 3256 (~0.3-0.4) and NGC 7469 (~0.3-0.5). The HCN (4-3)/HCN (3-2) intensity ratio in NGC 7469 has a slope of 1.34$\pm$0.05. We attribute the variation within NGC 3256 to excitation associated with the northern and southern nuclei. In NGC 7469, the variations are localized to the region surrounding the active galactic nucleus. At our resolution (~700 pc), IRAS 13120-5453 shows little variation in the HCN intensity ratios. Individual galaxies show nearly constant CN (2-1)/CN (1-0) intensity ratios. We find an offset to lower CN (2-1)/CN (1-0) intensity ratios (~0.5) in NGC 3256 compared to the other two galaxies (~0.8). For the CN (3-2)/CN (2-1) intensity ratio, NGC 7469 has a superlinear trend of 1.55$\pm$0.04, with the peak localized toward the active galactic nucleus. We find high (~1.7) CN (1-0)/HCN (1-0) intensity ratios in IRAS 13120-5453 and in the northern nucleus of NGC 3256, compared to a more constant ratio (~1.1) in NGC 7469 and non-starbursting regions of NGC 3256. △ Less

Submitted 16 April, 2021; originally announced April 2021.

Comments: 12 pages, 4 figures, 5 figures in Appendix, resubmitted to MNRAS after small revisions to address the first referee report

PHANGS-ALMA Data Processing and Pipeline

Authors: Adam K. Leroy, Annie Hughes, Daizhong Liu, Jerome Pety, Erik Rosolowsky, Toshiki Saito, Eva Schinnerer, Andreas Schruba, Antonio Usero, Christopher M. Faesi, Cinthya N. Herrera, Melanie Chevance, Alexander P. S. Hygate, Amanda A. Kepley, Eric W. Koch, Miguel Querejeta, Kazimierz Sliwa, David Will, Christine D. Wilson, Gagandeep S. Anand, Ashley Barnes, Francesco Belfiore, Ivana Beslic, Frank Bigiel, Guillermo A. Blanc , et al. (43 additional authors not shown)

Abstract: We describe the processing of the PHANGS-ALMA survey and present the PHANGS-ALMA pipeline, a public software package that processes calibrated interferometric and total power data into science-ready data products. PHANGS-ALMA is a large, high-resolution survey of CO J=2-1 emission from nearby galaxies. The observations combine ALMA's main 12-m array, the 7-m array, and total power observations and… ▽ More We describe the processing of the PHANGS-ALMA survey and present the PHANGS-ALMA pipeline, a public software package that processes calibrated interferometric and total power data into science-ready data products. PHANGS-ALMA is a large, high-resolution survey of CO J=2-1 emission from nearby galaxies. The observations combine ALMA's main 12-m array, the 7-m array, and total power observations and use mosaics of dozens to hundreds of individual pointings. We describe the processing of the u-v data, imaging and deconvolution, linear mosaicking, combining interferometer and total power data, noise estimation, masking, data product creation, and quality assurance. Our pipeline has a general design and can also be applied to VLA and ALMA observations of other spectral lines and continuum emission. We highlight our recipe for deconvolution of complex spectral line observations, which combines multiscale clean, single scale clean, and automatic mask generation in a way that appears robust and effective. We also emphasize our two-track approach to masking and data product creation. We construct one set of "broadly masked" data products, which have high completeness but significant contamination by noise, and another set of "strictly masked" data products, which have high confidence but exclude faint, low signal-to-noise emission. Our quality assurance tests, supported by simulations, demonstrate that 12-m+7-m deconvolved data recover a total flux that is significantly closer to the total power flux than the 7-m deconvolved data alone. In the appendices, we measure the stability of the ALMA total power calibration in PHANGS--ALMA and test the performance of popular short-spacing correction algorithms. △ Less

Submitted 14 April, 2021; originally announced April 2021.

Comments: Accepted for publication in the Astrophysical Journal Supplement series. 65 pages, 33 figures. Software available at https://github.com/akleroy/phangs_imaging_scripts . For a full resolution version see https://sites.google.com/view/phangs/publications

Highly turbulent gas on GMC-scales in NGC 3256, the nearest luminous infrared galaxy

Authors: Nathan Brunetti, Christine D. Wilson, Kazimierz Sliwa, Eva Schinnerer, Susanne Aalto, Alison B. Peck

Abstract: We present the highest resolution CO (2-1) observations obtained to date (0.25") of NGC 3256 and use them to determine the detailed properties of the molecular interstellar medium in the central 6 kpc of this merger. Distributions of physical quantities are reported from pixel-by-pixel measurements at 55 and 120 pc scales and compared to disc galaxies observed by PHANGS-ALMA. Mass surface densitie… ▽ More We present the highest resolution CO (2-1) observations obtained to date (0.25") of NGC 3256 and use them to determine the detailed properties of the molecular interstellar medium in the central 6 kpc of this merger. Distributions of physical quantities are reported from pixel-by-pixel measurements at 55 and 120 pc scales and compared to disc galaxies observed by PHANGS-ALMA. Mass surface densities range from 8 to 5500 M$_{\odot}$ pc$^{-2}$ and velocity dispersions from 10 to 200 km s$^{-1}$. Peak brightness temperatures as large as 37 K are measured, indicating the gas in NGC 3256 may be hotter than all regions in nearby disc galaxies measured by PHANGS-ALMA. Brightness temperatures even surpass those in the overlap region of NGC 4038/9 at the same scales. The majority of the gas appears unbound with median virial parameters of 7 to 19, although external pressure may bind some of the gas. High internal turbulent pressures of 10$^{5}$ to 10$^{10}$ K cm$^{-3}$ are found. Given the lack of significant trends in surface density, brightness temperature, and velocity dispersion with physical scale we argue the molecular gas is made up of a smooth medium down to 55 pc scales, unlike the more structured medium found in the PHANGS-ALMA disc galaxies. △ Less

Submitted 2 November, 2020; originally announced November 2020.

Comments: accepted to MNRAS, 21 pages, 8 figures

Physical properties of the ambient medium and of dense cores in the Perseus star-forming region derived from Herschel Gould Belt Survey observations

Authors: S. Pezzuto, M. Benedettini, J. Di Francesco, P. Palmeirim, S. Sadavoy, E. Schisano, G. Li Causi, Ph. André, D. Arzoumanian, J. -Ph. Bernard, S. Bontemps, D. Elia, E. Fiorellino, J. M. Kirk, V. Könyves, B. Ladjelate, A. Menshchikov, F. Motte, L. Piccotti, N. Schneider, L. Spinoglio, D. Ward-Thompson, C. D. Wilson

Abstract: (Abridged) In this paper, we present analyses of images taken with the Herschel ESA satellite from 70mu to 500mu. We first constructed column density and dust temperature maps. Next, we identified compact cores in the maps, and characterize the cores using modified blackbody fits to their SEDs: we identified 684 starless cores, of which 199 are bound and potential prestellar cores, and 132 protost… ▽ More (Abridged) In this paper, we present analyses of images taken with the Herschel ESA satellite from 70mu to 500mu. We first constructed column density and dust temperature maps. Next, we identified compact cores in the maps, and characterize the cores using modified blackbody fits to their SEDs: we identified 684 starless cores, of which 199 are bound and potential prestellar cores, and 132 protostars. We also matched the Herschel-identified young stars with GAIA sources to model distance variations across the Perseus cloud. We measure a linear gradient function with right ascension and declination for the entire cloud. From the SED fits, mass and temperature of cores were derived. The core mass function can be modelled with a log-normal distribution that peaks at 0.82~$M_\sun$ suggesting a star formation efficiency of 0.30. The high-mass tail can be modelled with a power law of slope $\sim-2.32$, close to the Salpeter's value. We also identify the filamentary structure of Perseus, confirming that stars form preferentially in filaments. We find that the majority of filaments where star formation is ongoing are transcritical against their own internal gravity because their linear masses are below the critical limit of 16~$M_\sun$pc$^{-1}$ above which we expect filaments to collapse. We find a possible explanation for this result, showing that a filament with a linear mass as low as 8~$M_\sun$pc$^{-1}$ can be already unstable. We confirm a linear relation between star formation efficiency and slope of dust probability density function and a similar relation is also seen with the core formation efficiency. We derive a lifetime for the prestellar core phase of $1.69\pm0.52$~Myr for Perseus but different regions have a wide range in prestellar core fractions, hint that star-formation has started only recently in some clumps. We also derive a free-fall time for prestellar cores of 0.16~Myr. △ Less

Submitted 4 November, 2020; v1 submitted 30 September, 2020; originally announced October 2020.

Comments: Comparison with Zari et al's (2016) work improved once Eleonora Zari told us that, contrarily to what we wrote, their data are publicly available (this was not written in the first version of their paper put on arxiv, then our misunderstaning). The modification is small, a paragraph on page 11, and does not have any impact on the content of the paper. Modification allowed by A&A editor

Journal ref: A&A 645, A55 (2021)

A new estimator of resolved molecular gas in nearby galaxies

Authors: Ryan Chown, Cheng Li, Laura C. Parker, Christine D. Wilson, Niu Li, Yang Gao

Abstract: A relationship between dust-reprocessed light from recent star formation and the amount of star-forming gas in a galaxy produces a correlation between WISE 12 $μ$m emission and CO line emission. Here we explore this correlation on kiloparsec scales with CO(1-0) maps from EDGE-CALIFA matched in resolution to WISE 12 $μ$m images. We find strong CO-12 $μ$m correlations within each galaxy and we show… ▽ More A relationship between dust-reprocessed light from recent star formation and the amount of star-forming gas in a galaxy produces a correlation between WISE 12 $μ$m emission and CO line emission. Here we explore this correlation on kiloparsec scales with CO(1-0) maps from EDGE-CALIFA matched in resolution to WISE 12 $μ$m images. We find strong CO-12 $μ$m correlations within each galaxy and we show that the scatter in the global CO-12 $μ$m correlation is largely driven by differences from galaxy to galaxy. The correlation is stronger than that between star formation rate and H$_2$ surface densities ($Σ(\mathrm{H_2})$). We explore multi-variable regression to predict $Σ(\mathrm{H_2})$ in star-forming pixels using the WISE 12 $μ$m data combined with global and resolved galaxy properties, and provide the fit parameters for the best estimators. We find that $Σ(\mathrm{H_2})$ estimators that include $Σ(\mathrm{12\>μm})$ are able to predict $Σ(\mathrm{H_2})$ more accurately than estimators that include resolved optical properties instead of $Σ(\mathrm{12\>μm})$. These results suggest that 12 $μ$m emission and H$_2$ as traced by CO emission are physically connected at kiloparsec scales. This may be due to a connection between polycyclic aromatic hydrocarbon (PAH) emission and the presence of H$_2$. The best single-property estimator is $\log \frac{Σ(\mathrm{H_2})}{\mathrm{M_\odot\>pc^{-2}}} = (0.48 \pm 0.01) + (0.71 \pm 0.01)\log \frac{Σ(\mathrm{12\>μm})}{\mathrm{L_\odot\>pc^{-2}}}$. This correlation can be used to efficiently estimate $Σ(\mathrm{H_2})$ down to at least $1 \> M_\odot \> \mathrm{pc^{-2}}$ in star-forming regions within nearby galaxies. △ Less

Submitted 15 September, 2020; v1 submitted 30 June, 2020; originally announced July 2020.

Comments: 19 pages, 8 figures, 6 tables, accepted by MNRAS. Data tables and a script for making 2D cutouts for each galaxy are available as MNRAS supplementary material and at https://lig.astro.tsinghua.edu.cn/astrodata/publication/20/estimator-resolved-molecular/

Is this an Early Stage Merger? A Case Study on Molecular Gas and Star Formation Properties of Arp 240

Authors: Hao He, C. D. Wilson, Kazimierz Sliwa, Daisuke Iono, Toshiki Saito

Abstract: We present new high resolution $^{12}$CO $J$=1-0, $J$=2-1, and $^{13}$CO $J$=1-0 maps of the early stage merger Arp 240 (NGC5257/8) obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Simulations in the literature suggest that the merger has just completed its first passage; however, we find that this system has a lower global gas fraction but a higher star formation efficiency… ▽ More We present new high resolution $^{12}$CO $J$=1-0, $J$=2-1, and $^{13}$CO $J$=1-0 maps of the early stage merger Arp 240 (NGC5257/8) obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Simulations in the literature suggest that the merger has just completed its first passage; however, we find that this system has a lower global gas fraction but a higher star formation efficiency compared to typical close galaxy pairs, which suggests that this system may already be in an advanced merger stage. We combine the ALMA data with $^{12}$CO $J$=3-2 observations from the Submillimeter Array and carry out RADEX modeling on several different regions. Both the RADEX modeling and a local thermal equilibrium (LTE) analysis show that the regions are most likely to have a CO-to-H$_2$ conversion factor $α_{\mathrm{CO}}$ close to or perhaps even smaller than the typical value for (ultra-)luminous infrared galaxies. Using 33 GHz data from the Very Large Array to measure the star formation rate, we find that most star forming regions have molecular gas depletion times of less than 100 Myr. We calculated the star formation efficiency (SFE) per free-fall time for different regions and find some regions appear to have values greater than 100%. We find these regions generally show evidence for young massive clusters (YMCs). After exploring various factors, we argue that this is mainly due to the fact that radio continuum emission in those regions is dominated by that from YMCs, which results in an overestimate of the SFE per free-fall time. △ Less

Submitted 22 June, 2020; originally announced June 2020.

Comments: 20 pages, 14 figures, accepted for publication in MNRAS

JINGLE -- IV. Dust, HI gas and metal scaling laws in the local Universe

Authors: I. De Looze, I. Lamperti, A. Saintonge, M. Relano, M. W. L. Smith, C. J. R. Clark, C. D. Wilson, M. Decleir, A. P. Jones, R. C. Kennicutt, G. Accurso, E. Brinks, M. Bureau, P. Cigan, D. L. Clements, P. De Vis, L Fanciullo, Y. Gao, W. K. Gear, L. C. Ho, H. S. Hwang, M. J. Michalowski, J. C. Lee, C. Li, L. Lin , et al. (7 additional authors not shown)

Abstract: Scaling laws of dust, HI gas and metal mass with stellar mass, specific star formation rate and metallicity are crucial to our understanding of the buildup of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass ($M_{\text{HI}}$/$M_{\star}$) across a diverse sample of 423 nearby galaxies. The observed trends a… ▽ More Scaling laws of dust, HI gas and metal mass with stellar mass, specific star formation rate and metallicity are crucial to our understanding of the buildup of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass ($M_{\text{HI}}$/$M_{\star}$) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) - incluidng stellar dust production, grain growth, and dust destruction - within a Bayesian framework to enable a rigorous search of the multi-dimensional parameter space. We find that these scaling laws for galaxies with $-1.0\lesssim \log M_{\text{HI}}$/$M_{\star}\lesssim0$ can be reproduced using closed-box models with high fractions (37-89$\%$) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies ($ε$=30-40), and long dus lifetimes (1-2\,Gyr). The models have present-day dust masses with similar contributions from stellar sources (50-80\,$\%$) and grain growth (20-50\,$\%$). Over the entire lifetime of these galaxies, the contribution from stardust ($>$90\,$\%$) outweighs the fraction of dust grown in the interstellar medium ($<$10$\%$). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth timescales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium. △ Less

Submitted 2 June, 2020; originally announced June 2020.

Comments: 56 pages, 30 figures, accepted for publication in MNRAS

The MALATANG Survey: Dense Gas and Star Formation from High Transition HCN and HCO+ maps of NGC253

Authors: Xue-Jian Jiang, Thomas R. Greve, Yu Gao, Zhi-Yu Zhang, Qinghua Tan, Richard de Grijs, Luis C. Ho, Michal J. Michalowski, Malcolm J. Currie, Christine D. Wilson, Elias Brinks, Yiping Ao, Yinghe Zhao, Jinhua He, Nanase Harada, Chentao Yang, Qian Jiao, Aeree Chung, Bumhyun Lee, Matthew W. L. Smith, Daizhong Liu, Satoki Matsushita, Yong Shi, Masatoshi Imanishi, Mark G. Rawlings , et al. (4 additional authors not shown)

Abstract: To study the high-transition dense-gas tracers and their relationships to the star formation of the inner $\sim$ 2 kpc circumnuclear region of NGC253, we present HCN $J=4-3$ and HCO$^+ J=4-3$ maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices $r_{90}/r_{50}$ for the different tracers. HCN and HCO$^+$ 4-3 emission feat… ▽ More To study the high-transition dense-gas tracers and their relationships to the star formation of the inner $\sim$ 2 kpc circumnuclear region of NGC253, we present HCN $J=4-3$ and HCO$^+ J=4-3$ maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices $r_{90}/r_{50}$ for the different tracers. HCN and HCO$^+$ 4-3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1-0 and the stellar component. The dense-gas fraction ($f_\text{dense}$, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO$^+$/CO) and the ratio $R_\text{31}$ (CO 3-2/1-0) decline towards larger galactocentric distances, but increase with higher SFR surface density. The radial variation and the large scatter of $f_\text{dense}$ and $R_\text{31}$ imply distinct physical conditions in different regions of the galactic disc. The relationships of $f_\text{dense}$ versus $Σ_\text{stellar}$, and SFE$_\text{dense}$ versus $Σ_\text{stellar}$ are explored. SFE$_\text{dense}$ increases with higher $Σ_\text{stellar}$ in this galaxy, which is inconsistent with previous work that used HCN 1-0 data. This implies that existing stellar components might have different effects on the high-$J$ HCN and HCO$^+$ than their low-$J$ emission. We also find that SFE$_\text{dense}$ seems to be decreasing with higher $f_\text{dense}$, which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars. △ Less

Submitted 14 March, 2020; originally announced March 2020.

Comments: accepted to MNRAS

[CI](1-0) and [CI](2-1) in resolved local galaxies

Authors: Alison F. Crocker, Eric Pellegrini, J. -D. T. Smith, Bruce T. Draine, Christine D. Wilson, Mark Wolfire, Lee Armus, Elias Brinks, Daniel A. Dale, Brent Groves, Rodrigo Herrera-Camus, Leslie K. Hunt, Robert C. Kennicutt, Eric J. Murphy, Karin Sandstrom, Eva Schinnerer, Dimitra Rigopoulou, Erik Rosolowsky, Paul van der Werf

Abstract: We present resolved [CI] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from $J_\mathrm{up} = 1$ to 7 to interpret what phase of the interstellar medium the [CI] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4… ▽ More We present resolved [CI] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from $J_\mathrm{up} = 1$ to 7 to interpret what phase of the interstellar medium the [CI] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4-3) and [CI](2-1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [CI] and CO line emission using large velocity gradient models combined with an empirical template. According to this modeling, the [CI](1-0) line is clearly dominated by the low-excitation component. We determine [CI] to molecular mass conversion factors for both the [CI](1-0) and [CI](2-1) lines, with mean values of $α_{\mathrm{[CI](1-0)}} = 7.3$ M$_{\mathrm{sun}}$ K$^{-1}$ km$^{-1}$ s pc$^{-2}$ and $α_{\mathrm{[CI](2-1)}} = 34 $ M$_{\mathrm{sun}}$ K$^{-1}$ km$^{-1}$ s pc$^{-2}$ with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of $α_{\mathrm{[CI](1-0)}}$ to $α_{\mathrm{CO}}$ (derived using the CO(2-1) line) suggests that [CI](1-0) may be just as good a tracer of cold molecular gas as CO(2-1) in galaxies of this type. On the other hand, the wider spread of $α_{\mathrm{[CI](2-1)}}$ and the tight relation found between [CI](2-1) and CO(4-3) suggest that much of the [CI](2-1) emission may originate in warmer molecular gas. △ Less

Submitted 14 January, 2020; originally announced January 2020.

Comments: 15 pages, 10 figures, published in ApJ

Journal ref: The Astrophysical Journal 887 (2019) 105

The HASHTAG project I. A Survey of CO(3-2) Emission from the Star Forming Disc of M31

Authors: Zongnan Li, Zhiyuan Li, Matthew W. L. Smith, Christine D. Wilson, Yu Gao, Stephen A. Eales, Yiping Ao, Martin Bureau, Aeree Chung, Timothy A. Davis, Richard de Grijs, David J. Eden, Jinhua He, Tom M. Hughes, Xuejian Jiang, Francisca Kemper, Isabella Lamperti, Bumhyun Lee, Chien-Hsiu Lee, Michal J. Michalowski, Harriet Parsons, Sarah Ragan, Peter Scicluna, Yong Shi, Xindi Tang , et al. (4 additional authors not shown)

Abstract: We present a CO(3-2) survey of selected regions in the M31 disc as part of the JCMT large programme, HARP and SCUBA-2 High-Resolution Terahertz Andromeda Galaxy Survey (HASHTAG). The 12 CO(3-2) fields in this survey cover a total area of 60 square arcminutes, spanning a deprojected radial range of 2 - 14 kpc across the M31 disc. Combining these observations with existing IRAM 30m CO(1-0) observati… ▽ More We present a CO(3-2) survey of selected regions in the M31 disc as part of the JCMT large programme, HARP and SCUBA-2 High-Resolution Terahertz Andromeda Galaxy Survey (HASHTAG). The 12 CO(3-2) fields in this survey cover a total area of 60 square arcminutes, spanning a deprojected radial range of 2 - 14 kpc across the M31 disc. Combining these observations with existing IRAM 30m CO(1-0) observations and JCMT CO(3-2) maps of the nuclear region of M31, as well as dust temperature and star formation rate surface density maps, we are able to explore the radial distribution of the CO(3-2)/CO(1-0) integrated intensity ratio (R31) and its relationship with dust temperature and star formation. We find that the value of R31 between 2 - 9 kpc galactocentric radius is 0.14, significantly lower than what is seen in the nuclear ring at ~1 kpc (R31 ~ 0.8), only to rise again to 0.27 for the fields centred on the 10 kpc star forming ring. We also found that R31 is positively correlated with dust temperature, with Spearman's rank correlation coefficient $ρ$ = 0.55. The correlation between star formation rate surface density and CO(3--2) intensity is much stronger than with CO(1-0), with $ρ$ = 0.54 compared to -0.05, suggesting that the CO(3-2) line traces warmer and denser star forming gas better. We also find that R31 correlates well with star formation rate surface density, with $ρ$ = 0.69. △ Less

Submitted 5 December, 2019; originally announced December 2019.

Comments: 21 pages, 10 figures, accepted by MNRAS for publication

The CO(3-2)/CO(1-0) luminosity line ratio in nearby star-forming galaxies and AGN from xCOLD GASS, BASS and SLUGS

Authors: Isabella Lamperti, Amélie Saintonge, Michael Koss, Serena Viti, Christine D. Wilson, Hao He, T. Taro Shimizu, Thomas R. Greve, Richard Mushotzky, Ezequiel Treister, Carsten Kramer, David Sanders, Kevin Schawinski, Linda J. Tacconi

Abstract: We study the r31=L'CO(3-2)/L'CO(1-0) luminosity line ratio in a sample of nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray selected AGN host galaxies from BASS and 37 infrared luminous galaxies from SLUGS. We find a trend for r31 to increase with star-formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density i… ▽ More We study the r31=L'CO(3-2)/L'CO(1-0) luminosity line ratio in a sample of nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray selected AGN host galaxies from BASS and 37 infrared luminous galaxies from SLUGS. We find a trend for r31 to increase with star-formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density is the main parameter responsible for variation of r31, while the interstellar radiation field and cosmic ray ionization rate play only a minor role. We interpret these results to indicate a relation between SFE and gas density. We do not find a difference in the r31 value of SFGs and AGN host galaxies, when the galaxies are matched in SSFR (<r31>= 0.52 +/- 0.04 for SFGs and <r31> = 0.53 +/- 0.06 for AGN hosts). According to the results of UCL-PDR models, the X-rays can contribute to the enhancement of the CO line ratio, but only for strong X-ray fluxes and for high gas density (nH > 10$^4$ cm-3). We find a mild tightening of the Kennicutt-Schmidt relation when we use the molecular gas mass surface density traced by CO(3-2) (Pearson correlation coefficient R=0.83), instead of the molecular gas mass surface density traced by CO(1-0) (R=0.78), but the increase in correlation is not statistically significant (p-value=0.06). This suggests that the CO(3-2) line can be reliably used to study the relation between SFR and molecular gas for normal SFGs at high redshift, and to compare it with studies of low-redshift galaxies, as is common practice. △ Less

Submitted 2 December, 2019; originally announced December 2019.

Estimating the molecular gas mass of low-redshift galaxies from a combination of mid-infrared luminosity and optical properties

Authors: Yang Gao, Ting Xiao, Cheng Li, Xue-Jian Jiang, Qing-hua Tan, Yu Gao, Christine D. Wilson, Martin Bureau, Amelie Saintonge, Jos'e R. S'anchez-Gallego, Toby Brown, Christopher J. Clark, Ho Seong Hwang, Isabella Lamperti, Lin Lin, Lijie Liu, Dengrong Lu, Hsi-An Pan, Jixian Sun, Thomas G. Williams

Abstract: We present CO(J=1-0) and/or CO(J=2-1) spectroscopy for 31 galaxies selected from the ongoing MaNGA survey, obtained with multiple telescopes. This sample is combined with CO observations from the literature to study the correlation of the CO luminosities ($L_{\rm CO(1-0)}$) with the mid-infrared luminosities at 12 ($L_{12 μm}$) and 22 $μ$m ($L_{\rm 22 μm}$), as well as the dependence of the residu… ▽ More We present CO(J=1-0) and/or CO(J=2-1) spectroscopy for 31 galaxies selected from the ongoing MaNGA survey, obtained with multiple telescopes. This sample is combined with CO observations from the literature to study the correlation of the CO luminosities ($L_{\rm CO(1-0)}$) with the mid-infrared luminosities at 12 ($L_{12 μm}$) and 22 $μ$m ($L_{\rm 22 μm}$), as well as the dependence of the residuals on a variety of galaxy properties. The correlation with $L_{\rm 12 μm}$ is tighter and more linear, but galaxies with relatively low stellar masses and blue colors fall significantly below the mean $L_{\rm CO(1-0)}-L_{\rm 12μm}$ relation. We propose a new estimator of the CO(1-0) luminosity (and thus the total molecular gas mass) that is a linear combination of three parameters: $L_{\rm 12 μm}$, $M_\ast$ and $g-r$. We show that, with a scatter of only 0.18 dex in log $(L_{\rm CO(1-0)})$, this estimator provides unbiased estimates for galaxies of different properties and types. An immediate application of this estimator to a compiled sample of galaxies with only CO(J=2-1) observations yields a distribution of the CO(J=2-1) to CO(J=1-0) luminosity ratios ($R21$) that agrees well with the distribution of real observations, in terms of both the median and the shape. Application of our estimator to the current MaNGA sample reveals a gas-poor population of galaxies that are predominantly early-type and show no correlation between molecular gas-to-stellar mass ratio and star formation rate, in contrast to gas-rich galaxies. We also provide alternative estimators with similar scatters, based on $r$ and/or $z$ band luminosities instead of $M_\ast$. These estimators serve as cheap and convenient $M_{\rm mol}$ proxies to be potentially applied to large samples of galaxies, thus allowing statistical studies of gas-related processes of galaxies. △ Less

Submitted 10 November, 2019; v1 submitted 7 November, 2019; originally announced November 2019.

Comments: 24 pages, 12 figures, accepted for publication in ApJ

Development Plans for the Atacama Large Millimeter/submillimeter Array (ALMA)

Authors: Christine Wilson, Scott Chapman, Ruobing Dong, James di Francesco, Laura Fissel, Doug Johnstone, Helen Kirk, Brenda Matthews, Brian McNamara, Erik Rosolowsky, Michael Rupen, Sarah Sadavoy, Douglas Scott, Nienke van der Marel

Abstract: (abridged) The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Canadian Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with first science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record n… ▽ More (abridged) The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Canadian Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with first science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record numbers of proposals submitted to the annual calls and large numbers of highly cited scientific papers across fields from protoplanetary disks to high-redshift galaxies and quasars. The LRP2010 ALMA white paper laid out 8 specific metrics that could be used to judge the success of Canada's participation in ALMA. Among these metrics were publications (number; impact), collaborations (international; multi-wavelength), and student training. To call out one particular metric, Canadians are making excellent use of ALMA in training graduate students and postdocs: as of June 2018, 12 of 23 Canadian first-author papers were led by a graduate student, and a further 4 papers were led by postdocs. All 8 metrics argue for Canada's involvement in ALMA over the past decade to be judged a success. The successful achievement of these wide-ranging goals argues strongly for Canada's continuing participation in ALMA over the next decade and beyond. Looking forward, our community needs to: (1) maintain Canadian access to ALMA and our competitiveness in using ALMA; (2) preserve full Canadian funding for our share of ALMA operations; (3) identify components of ALMA development in which Canada can play a significant role, including stimulating expertise in submillimetre instrumentation to capitalize on future opportunities; and (4) keep Canadians fully trained and engaged in ALMA, as new capabilities become available, reaching the widest possible community of potential users. △ Less

Submitted 9 October, 2019; originally announced October 2019.

Comments: White paper E004 submitted to the Canadian Long Range Plan 2020

JINGLE V: Dust properties of nearby galaxies derived from hierarchical Bayesian SED fitting

Authors: Isabella Lamperti, Amélie Saintonge, Ilse De Looze, Gioacchino Accurso, Christopher J. R. Clark, Matthew W. L. Smith, Christine D. Wilson, Elias Brinks, Toby Brown, Martin Bureau, David L. Clements, Stephen Eales, David H. W. Glass, Ho Seong Hwang, Jong Chul Lee, Lihwai Lin, Michal J. Michalowski, Mark Sargent, Thomas G. Williams, Ting Xiao, Chentao Yang

Abstract: We study the dust properties of 192 nearby galaxies from the JINGLE survey using photometric data in the 22-850micron range. We derive the total dust mass, temperature T and emissivity index beta of the galaxies through the fitting of their spectral energy distribution (SED) using a single modified black-body model (SMBB). We apply a hierarchical Bayesian approach that reduces the known degeneracy… ▽ More We study the dust properties of 192 nearby galaxies from the JINGLE survey using photometric data in the 22-850micron range. We derive the total dust mass, temperature T and emissivity index beta of the galaxies through the fitting of their spectral energy distribution (SED) using a single modified black-body model (SMBB). We apply a hierarchical Bayesian approach that reduces the known degeneracy between T and beta. Applying the hierarchical approach, the strength of the T-beta anti-correlation is reduced from a Pearson correlation coefficient R=-0.79 to R=-0.52. For the JINGLE galaxies we measure dust temperatures in the range 17-30 K and dust emissivity indices beta in the range 0.6-2.2. We compare the SMBB model with the broken emissivity modified black-body (BMBB) and the two modified black-bodies (TMBB) models. The results derived with the SMBB and TMBB are in good agreement, thus applying the SMBB, which comes with fewer free parameters, does not penalize the measurement of the cold dust properties in the JINGLE sample. We investigate the relation between T and beta and other global galaxy properties in the JINGLE and Herschel Reference Survey (HRS) sample. We find that beta correlates with the stellar mass surface density (R=0.62) and anti-correlates with the HI mass fraction (M(HI)/M*, R=-0.65), whereas the dust temperature correlates strongly with the SFR normalized by the dust mass (R=0.73). These relations can be used to estimate T and beta in galaxies with insufficient photometric data available to measure them directly through SED fitting. △ Less

Submitted 11 September, 2019; originally announced September 2019.

Comments: MNRAS in press, 31 pages

The Kennicutt-Schmidt Law and Gas Scale Height in Luminous and Ultra-Luminous Infrared Galaxies

Authors: Christine D. Wilson, Bruce G. Elmegreen, Ashley Bemis, Nathan Brunetti

Abstract: A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to $1.74^{+0.09}_{\rm -0.07}$ for gas surface densities $Σ_{\rm mol}>10^3\;M_\odot$ pc$^{-2}$ and an assumed constant CO-to-H$_2$ conversion factor. The velocity dispersion of the CO line,… ▽ More A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to $1.74^{+0.09}_{\rm -0.07}$ for gas surface densities $Σ_{\rm mol}>10^3\;M_\odot$ pc$^{-2}$ and an assumed constant CO-to-H$_2$ conversion factor. The velocity dispersion of the CO line, $σ_v$, scales approximately as the inverse square root of $Σ_{\rm mol}$, making the empirical gas scale height determined from $H\sim0.5σ^2/(πGΣ_{\rm mol})$ nearly constant, 150-190 pc, over 1.5 orders of magnitude in $Σ_{\rm mol}$. This constancy of $H$ implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which, in turn, implies that the gas dynamical rate (the inverse of the free-fall time) varies with $Σ_{\rm mol}^{1/2}$, thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per free-fall time is roughly constant, 5%-7%, and the gas depletion time decreases at high $Σ_{\rm mol}$, reaching only $\sim 16$ Myr at $Σ_{\rm mol}\sim10^4\;M_\odot$ pc$^{-2}$. The variation of $σ_v$ with $Σ_{\rm mol}$ and the constancy of $H$ are in tension with some feedback-driven models, which predict $σ_v$ to be more constant and $H$ to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre $Q$ instability parameter. △ Less

Submitted 11 July, 2019; originally announced July 2019.

Comments: Accepted to ApJ. 13 pages, 3 figures, 1 table. Supplementary data table used to generate the plots is included

A single fast radio burst localized to a massive galaxy at cosmological distance

Authors: K. W. Bannister, A. T. Deller, C. Phillips, J. -P. Macquart, J. X. Prochaska, N. Tejos, S. D. Ryder, E. M. Sadler, R. M. Shannon, S. Simha, C. K. Day, M. McQuinn, F. O. North-Hickey, S. Bhandari, W. R. Arcus, V. N. Bennert, J. Burchett, M. Bouwhuis, R. Dodson, R. D. Ekers, W. Farah, C. Flynn, C. W. James, M. Kerr, E. Lenc , et al. (29 additional authors not shown)

Abstract: Fast Radio Bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Non-repeating FRB observations have had insufficient positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single pulse FRB 180924 to a position 4 kpc from the center of a luminous galaxy at redshi… ▽ More Fast Radio Bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Non-repeating FRB observations have had insufficient positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single pulse FRB 180924 to a position 4 kpc from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web. △ Less

Submitted 27 June, 2019; originally announced June 2019.

Comments: Published online in Science 27 June 2019

JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: II. SCUBA-2 850 μm data reduction and dust flux density catalogues

Authors: Matthew W. L. Smith, Christopher J. R. Clark, Ilse De Looze, Isabella Lamperti, Amélie Saintonge, Christine D. Wilson, Gioacchino Accurso, Elias Brinks, Martin Bureau, Eun Jung Chung, Phillip J. Cigan, David L. Clements, Thavisha Dharmawardena, Lapo Fanciullo, Yang Gao, Yu Gao, Walter K. Gear, Haley L. Gomez, Joshua Greenslade, Ho Seong Hwang, Francisca Kemper, Jong Chul Lee, Cheng Li, Lihwai Lin, Lijie Liu , et al. (11 additional authors not shown)

Abstract: We present the SCUBA-2 850 $μm$ component of JINGLE, the new JCMT large survey for dust and gas in nearby galaxies, which with 193 galaxies is the largest targeted survey of nearby galaxies at 850 $μm$. We provide details of our SCUBA-2 data reduction pipeline, optimised for slightly extended sources, and including a calibration model adjusted to match conventions used in other far-infrared data.… ▽ More We present the SCUBA-2 850 $μm$ component of JINGLE, the new JCMT large survey for dust and gas in nearby galaxies, which with 193 galaxies is the largest targeted survey of nearby galaxies at 850 $μm$. We provide details of our SCUBA-2 data reduction pipeline, optimised for slightly extended sources, and including a calibration model adjusted to match conventions used in other far-infrared data. We measure total integrated fluxes for the entire JINGLE sample in 10 infrared/submillimetre bands, including all WISE, Herschel-PACS, Herschel-SPIRE and SCUBA-2 850 $μm$ maps, statistically accounting for the contamination by CO(J=3-2) in the 850 $μm$ band. Of our initial sample of 193 galaxies, 191 are detected at 250 $μm$ with a $\geq$ 5$σ$ significance. In the SCUBA-2 850 $μm$ band we detect 126 galaxies with $\geq$ 3$σ$ significance. The distribution of the JINGLE galaxies in far-infrared/sub-millimetre colour-colour plots reveals that the sample is not well fit by single modified-blackbody models that assume a single dust-emissivity index $(β)$. Instead, our new 850 $μm$ data suggest either that a large fraction of our objects require $β< 1.5$, or that a model allowing for an excess of sub-mm emission (e.g., a broken dust emissivity law, or a very cold dust component 10 K) is required. We provide relations to convert far-infrared colours to dust temperature and $β$ for JINGLE-like galaxies. For JINGLE the FIR colours correlate more strongly with star-formation rate surface-density rather than the stellar surface-density, suggesting heating of dust is greater due to younger rather than older stellar-populations, consistent with the low proportion of early-type galaxies in the sample. △ Less

Submitted 23 April, 2019; originally announced April 2019.

Comments: Accepted by MNRAS; data available at http://www.star.ucl.ac.uk/JINGLE/

New Insights into the Physical Conditions and Internal Structure of a Candidate Proto-Globular Cluster

Authors: Molly K. Finn, Kelsey E. Johnson, Crystal L. Brogan, Christine D. Wilson, Remy Indebetouw, William E. Harris, Julia Kamenetzky, Ashley Bemis

Abstract: We present $\sim$0.1" resolution ($\sim$10 pc) ALMA observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the ``Firecracker.' Since star formation has not yet begun at an appreciable level, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars form and dis… ▽ More We present $\sim$0.1" resolution ($\sim$10 pc) ALMA observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the ``Firecracker.' Since star formation has not yet begun at an appreciable level, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars form and disrupt the natal conditions. Using emission from $^{12}$CO(2-1), $^{12}$CO(3-2), $^{13}$CO(2-1), HCN(4-3), and HCO$^+$(4-3), we are able to resolve the cloud's structure and find that it has a characteristic radius of 22 pc and a mass of 1--9$\times10^6 M_\odot$. We also constrain the abundance ratios of $^{12}$CO/$^{13}$CO and H$_2$/\twelveCO. Based on the calculated mass, we determine that the commonly used CO-to-H$_2$ conversion factor varies spatially, with average values in the range $X_{CO}=(0.12-1.1)\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We demonstrate that if the cloud is bound (as is circumstantially suggested by its bright, compact morphology), an external pressure of $P/k > 10^8$ K cm$^{-3}$ is required. This would be consistent with theoretical expectations that globular cluster formation requires high pressure environments. The position-velocity diagram of the cloud and its surrounding material suggests that this pressure may be produced by the collision of filaments. The radial profile of the column density can be fit with both a Gaussian and Bonnor-Ebert profile. The relative line strengths of HCN and HCO$^+$ in this region suggest that these molecular lines can be used as tracers for the evolutionary stage of a cluster. △ Less

Submitted 20 March, 2019; originally announced March 2019.

Comments: 18 pages, 14 figures, Accepted to ApJ 2019 March 4

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution - Survey Description and Compact Source Catalogue

Authors: D. J. Eden, Tie Liu, Kee-Tae Kim, S. -Y. Liu, K. Tatematsu, J. Di Francesco, K. Wang, Y. Wu, M. A. Thompson, G. A. Fuller, Di Li, I. Ristorcelli, Sung-ju Kang, N. Hirano, D. Johnstone, Y. Lin, J. H. He, P. M. Koch, Patricio Sanhueza, S. -L. Qin, Q. Zhang, P. F. Goldsmith, N. J. Evans II, J. Yuan, C. -P. Zhang , et al. (136 additional authors not shown)

Abstract: We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850-um continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14… ▽ More We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850-um continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14.4 arcsec, significantly improving upon the 353-GHz resolution of Planck at 5 arcmin, and allowing for a catalogue of 3528 compact sources in 558 PGCCs. We find that the detected PGCCs have significant sub-structure, with 61 per cent of detected PGCCs having 3 or more compact sources, with filamentary structure also prevalent within the sample. A detection rate of 45 per cent is found across the survey, which is 95 per cent complete to Planck column densities of $N_{H_{2}}$ $>$ 5 $\times$ 10$^{21}$ cm$^{-2}$. By positionally associating the SCOPE compact sources with YSOs, the star formation efficiency, as measured by the ratio of luminosity to mass, in nearby clouds is found to be similar to that in the more distant Galactic Plane, with the column density distributions also indistinguishable from each other. △ Less

Submitted 26 February, 2019; originally announced February 2019.

Comments: 16 pages, 13 figures, 1 table. Accepted for publication in MNRAS

An ALMA archival study of the clump mass function in the Large Magellanic Cloud

Authors: Nathan Brunetti, Christine D. Wilson

Abstract: We present 1.3 and 3.2 mm continuum maps of three star forming regions in the Large Magellanic Cloud (LMC) observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). The data were taken as part of two projects retrieved from the ALMA public archive plus one project observed specifically for this work. We develop a technique to combine maps at these wavelengths to estimate dust-only emi… ▽ More We present 1.3 and 3.2 mm continuum maps of three star forming regions in the Large Magellanic Cloud (LMC) observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). The data were taken as part of two projects retrieved from the ALMA public archive plus one project observed specifically for this work. We develop a technique to combine maps at these wavelengths to estimate dust-only emission corrected for free-free emission contamination. From these observations we identify 32 molecular clumps in the LMC and estimate their total mass from their dust emission to range from 205 to 5740 M$_{\odot}$. We derive a cumulative clump mass function ($N(\geq M) \propto M^{α+ 1}$) and fit it with a double power law to find $α_{\mathrm{low}} = -1.76^{+0.04}_{-0.05}$, $α_{\mathrm{high}} = -3.3 \pm 0.2$, and a break mass of 2500$^{+300}_{-200}$ M$_{\odot}$. A comparison to the 30 Doradus-10 mass function derived previously from CO (2-1) data reveals a consistent range of clump masses and good agreement between the fitted slopes. We also find that the low mass index of the LMC mass function agrees well with the high mass index for core and clump mass functions from several star forming regions in the Milky Way. This agreement may indicate an extension of the Milky Way power law to higher masses than previously observed. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Comments: accepted to MNRAS; 18 pages, 11 figures

The Effect of Galaxy Interactions on Molecular Gas Properties

Authors: Hsi-An Pan, Lihwai Lin, Bau-Ching Hsieh, Ting Xiao, Yang Gao, Sara L. Ellison, Jillian M. Scudder, Jorge Barrera-Ballesteros, Fangting Yuan, Amélie Saintonge, Christine D. Wilson, Ho Seong Hwang, Ilse De Looze, Yu Gao, Luis C. Ho, Elias Brinks, Angus Mok, Toby Brown, Timothy A. Davis, Thomas G. Williams, Aeree Chung, Harriet Parsons, Martin Bureau, Mark T. Sargent, Eun Jung Chung , et al. (4 additional authors not shown)

Abstract: Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether, and by how much, galaxy interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecul… ▽ More Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether, and by how much, galaxy interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecular gas properties are determined from observations with the JCMT, PMO, CSO telescopes, and supplemented with data from the xCOLD GASS and JINGLE surveys at $^{12}$CO(1-0) and $^{12}$CO(2-1). The SFR, gas mass ($M_\mathrm{H_{2}}$), and gas fraction ($f_{gas}$) are all enhanced in galaxies in pairs by $\sim$ 2.5 times compared to the controls matched in redshift, mass, and effective radius, while the enhancement of star formation efficiency (SFE $\equiv$ SFR/$M_{H_{2}}$) is less than a factor of 2. We also find that the enhancements in SFR, $M_{H_{2}}$ and $f_{gas}$ increase with decreasing pair separation and are larger in systems with smaller stellar mass ratio. Conversely, the SFE is only enhanced in close pairs (separation $<$ 20 kpc) and equal-mass systems; therefore most galaxies in pairs lie in the same parameter space on the SFR-$M_{H_{2}}$ plane as controls. This is the first time that the dependence of molecular gas properties on merger configurations is probed statistically with a relatively large sample and with a carefully-selected control sample for individual galaxies. We conclude that galaxy interactions do modify the molecular gas properties, although the strength of the effect is merger configuration dependent. △ Less

Submitted 23 October, 2018; originally announced October 2018.

Comments: 26 pages, 11 figures, accepted for publication in ApJ

Linking bar- and interaction-driven molecular gas concentration with centrally-enhanced star formation in EDGE-CALIFA galaxies

Authors: Ryan Chown, Cheng Li, E. Athanassoula, Niu Li, Christine D. Wilson, Lin Lin, Houjun Mo, Laura C. Parker, Ting Xiao

Abstract: We study the spatially resolved star formation history and molecular gas distribution of 58 nearby galaxies, using integral field spectroscopy from the CALIFA survey and CO $J=1\rightarrow 0$ intensity mapping from the CARMA EDGE survey. We use the 4000 Å break (D$_n$4000), the equivalent width of the H$δ$ absorption line (EW H$δ_A$), and the equivalent width of the H$α$ emission line (EW H$α$) to… ▽ More We study the spatially resolved star formation history and molecular gas distribution of 58 nearby galaxies, using integral field spectroscopy from the CALIFA survey and CO $J=1\rightarrow 0$ intensity mapping from the CARMA EDGE survey. We use the 4000 Å break (D$_n$4000), the equivalent width of the H$δ$ absorption line (EW H$δ_A$), and the equivalent width of the H$α$ emission line (EW H$α$) to measure the recent star formation history (SFH) of these galaxies. We measure radial profiles of the three SFH indicators and molecular gas mass surface density, from which we measure the level of centrally enhanced star formation and the molecular gas concentration. When we separate our galaxies into categories of barred (17 galaxies), unbarred (24 galaxies), and merging/paired (17 galaxies) we find that the galaxies which have centrally-enhanced star formation (19/58) are either barred (13/19) or in mergers/pairs (6/19) with relatively high molecular gas concentrations. A comparison between our barred galaxies and a snapshot of a hydrodynamic $N$-body simulation of a barred galaxy shows that the current theory of bar formation and evolution can qualitatively reproduce the main features of the observed galaxies in our sample, including both the sharp decrease of stellar age in the galactic center and the gradual decrease of age with increasing distance from center. These findings provide substantial evidence for a picture in which cold gas is transported inward by a bar or tidal interaction, which leads to the growth and rejuvenation of star formation in the central region. △ Less

Submitted 4 February, 2019; v1 submitted 19 October, 2018; originally announced October 2018.

Comments: Accepted by MNRAS

JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: I. Survey overview and first results

Authors: Amelie Saintonge, Christine D. Wilson, Ting Xiao, Lihwai Lin, Ho Seong Hwang, Tomoka Tosaki, Martin Bureau, Phillip J. Cigan, Christopher J. R. Clark, David L. Clements, Ilse De Looze, Thavisha Dharmawardena, Yang Gao, Walter K. Gear, Joshua Greenslade, Isabella Lamperti, Jong Chul Lee, Cheng Li, Michal J. Michalowski, Angus Mok, Hsi-An Pan, Anne E. Sansom, Mark Sargent, Matthew W. L. Smith, Thomas Williams , et al. (66 additional authors not shown)

Abstract: JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in the local Universe. As part of the survey we perform 850um continuum measurements with SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M*>10^9Msun, as well as integrated CO(2-1) line fluxes with RxA3m for a subset of 90 of these galaxies. The sample is selected… ▽ More JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in the local Universe. As part of the survey we perform 850um continuum measurements with SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M*>10^9Msun, as well as integrated CO(2-1) line fluxes with RxA3m for a subset of 90 of these galaxies. The sample is selected from fields covered by the Herschel-ATLAS survey that are also targeted by the MaNGA optical integral-field spectroscopic survey. The new JCMT observations combined with the multi-wavelength ancillary data will allow for the robust characterization of the properties of dust in the nearby Universe, and the benchmarking of scaling relations between dust, gas, and global galaxy properties. In this paper we give an overview of the survey objectives and details about the sample selection and JCMT observations, present a consistent 30 band UV-to-FIR photometric catalog with derived properties, and introduce the JINGLE Main Data Release (MDR). Science highlights include the non-linearity of the relation between 850um luminosity and CO line luminosity, and the serendipitous discovery of candidate z>6 galaxies. △ Less

Submitted 19 September, 2018; originally announced September 2018.

Comments: MNRAS in press, 25 pages

Comprehensive comparison of models for spectral energy distributions from 0.1 micron to 1 mm of nearby star-forming galaxies

Authors: L. K. Hunt, I. De Looze, M. Boquien, R. Nikutta, A. Rossi, S. Bianchi, D. A. Dale, G. L. Granato, R. C. Kennicutt, L. Silva, L. Ciesla, M. Relano, S. Viaene, B. Brandl, D. Calzetti, K. V. Croxall, B. T. Draine, M. Galametz, K. D. Gordon, B. A. Groves, G. Helou, R. Herrera-Camus, J. L. Hinz, J. Koda, S. Salim , et al. (4 additional authors not shown)

Abstract: We have fit the far-ultraviolet (FUV) to sub-millimeter (850 micron) spectral energy distributions (SEDs) of the 61 galaxies from the "Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel" (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multi-wavelength Analysis of… ▽ More We have fit the far-ultraviolet (FUV) to sub-millimeter (850 micron) spectral energy distributions (SEDs) of the 61 galaxies from the "Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel" (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multi-wavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple "recipes" for stellar mass (Mstar), star-formation rate (SFR), dust mass (Mdust), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime, in particular between 25 and 70 micron where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard "recipes" for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a "standard" constant stellar mass-to-light ratio overestimates Mstar relative to the SED fitting, and we provide new SED-based formulations for estimating Mstar from WISE W1 (3.4 micron) luminosities and colors. From a Principal Component Analysis of Mstar, SFR, Mdust, and O/H, we reproduce previous scaling relations among Mstar, SFR, and O/H, and find that Mdust can be predicted to within roughly 0.3 dex using only Mstar and SFR. △ Less

Submitted 13 November, 2018; v1 submitted 11 September, 2018; originally announced September 2018.

Comments: 42 pages, 23 figures, 8 tables, 2 appendices: updated to v2, A&A, accepted

Journal ref: A&A 621, A51 (2019)