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Morphologies of SAGAbg low-mass galaxies in Legacy Survey multi-band imaging: dependence on stellar masses, star-formation rates and low-redshift evolution
Authors:
Joy Bhattacharyya,
Guinevere Herron,
Yasmeen Asali,
Abby Mintz,
Mithi A. C. de los Reyes,
Yao-Yuan Mao,
Annika H. G. Peter
Abstract:
The optical morphologies of low-mass galaxies can be used to directly trace their assembly and constrain models of galaxy evolution. We select a sample of 6211 low-mass ($7\lesssim {\rm log}(M_{\ast}/M_{\odot})\lesssim 10$) star-forming galaxies from the SAGAbg catalog that has high-completeness at low-redshifts ($z<0.1$). We obtain their galaxy maps in the $griz$ - bands of the Legacy Surveys and…
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The optical morphologies of low-mass galaxies can be used to directly trace their assembly and constrain models of galaxy evolution. We select a sample of 6211 low-mass ($7\lesssim {\rm log}(M_{\ast}/M_{\odot})\lesssim 10$) star-forming galaxies from the SAGAbg catalog that has high-completeness at low-redshifts ($z<0.1$). We obtain their galaxy maps in the $griz$ - bands of the Legacy Surveys and apply STATMORPH to calculate non-parametric morphological measures including the Gini index, $M_{20}$ measure, and CAS parameters. We study how resolution and signal-to-noise affect the morphology measures and find that the bulge strength measurements are the most reliable. The sequence in Gini$-M_{20}$ space is directly linked to the star-forming sequence of galaxies and is dominated by Sb/Sc/Ir morphologies. The $g$-band light distributions are the least concentrated among all the bands. The systematic trends of $M_{20}$ with respect to stellar mass and GALEX NUV-derived specific star formation rate (sSFR) strongly indicate that the galaxies with flatter light profiles are less massive with higher sSFR and vice-versa. We statistically infer that star-forming low-mass galaxies predominantly have disk morphologies with bulges becoming more prominent in quenched systems at higher masses (${\rm log}(M_{\ast}/M_{\odot})\gtrsim 9$).
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Submitted 17 July, 2026;
originally announced July 2026.
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Everything Every Band All at Once I: A Global Morphology Catalog in Abell 2744 based on UNCOVER/MegaScience
Authors:
Yunchong Zhang,
Tim B. Miller,
Sedona H. Price,
Katherine A. Suess,
Rachel Bezanson,
David J. Setton,
Joel Leja,
Katherine E. Whitaker,
Jenny E. Greene,
Robert Feldmann,
Seiji Fujimoto,
Themiya Nanayakkara,
Gabriel Brammer,
Sam E. Cutler,
Pratika Dayal,
Anna de Graaff,
Yoshinobu Fudamoto,
Lukas J. Furtak,
Andy D. Goulding,
Gourav Khullar,
Ivo Labbe,
Brian Lorenz,
Danilo Marchesini,
Abby Mintz,
Lamiya A. Mowla
, et al. (9 additional authors not shown)
Abstract:
We present spectrally-resolved structural parameter measurements of 28,274 sources from the legacy lensing field of Abell 2744, quantifying global structures from observed $0.7 μm - 4.8 μm$ and spanning rest-frame UV to NIR at $R\sim15$. These measurements are made on imaging mosaics mainly from the UNCOVER/MegaScience survey, including 20 JWST NIRCam broad and medium bands. We perform single-comp…
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We present spectrally-resolved structural parameter measurements of 28,274 sources from the legacy lensing field of Abell 2744, quantifying global structures from observed $0.7 μm - 4.8 μm$ and spanning rest-frame UV to NIR at $R\sim15$. These measurements are made on imaging mosaics mainly from the UNCOVER/MegaScience survey, including 20 JWST NIRCam broad and medium bands. We perform single-component Sérsic fitting to these galaxies using \texttt{pysersic}, a Bayesian structural fitting tool, to infer their structural parameters and associated random uncertainties from the posterior distributions. Through various quality evaluation criteria, we infer robust structural parameters among $> 85\%$ of the selected $\rm SNR>10$ sources. For each galaxy with reliable sizes in at least two bands and a high quality redshift, we fit its observed size as a function of wavelength and infer rest-frame UV, optical, and near-infrared sizes where applicable. By performing injection-recovery tests on simulated galaxy cutouts in selected bands, we establish that our structural parameter measurements achieve fractional error $< 10 -20\%$ above $\rm SNR>10$. With this paper, all raw structural measurements and fitted rest-frame sizes are quality-flagged, cataloged, and released to the community. Finally, we demonstrate that this catalog enables the structural study of galaxies over an unprecedentedly wide parameter space of redshift ($0.3<z<8$), stellar mass ($\rm 10^{7}\, M_{\odot}<M_{*} <10^{11.5}\, M_{\odot}$), and rest-frame optical size ($\rm 100 \,pc<R_{e}<10\,kpc$), after correcting for lensing magnification.
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Submitted 4 August, 2026; v1 submitted 27 February, 2026;
originally announced March 2026.
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Evidence for Shallow Nebular Attenuation Curves and Patchy Dust Geometry at z~2 with Pa-beta/H-alpha Measurements from JWST-MegaScience Medium Band Photometry
Authors:
Brian Lorenz,
Katherine A. Suess,
Mariska Kriek,
Sedona H. Price,
Joel Leja,
Hakim Atek,
Abhiyan Barailee,
Rachel Bezanson,
Gabriel Brammer,
Sam E. Cutler,
Pratika Dayal,
Anna de Graaf,
Jenny E. Greene,
Lukas J. Furtak,
Ivo Labbe,
Danilo Marchesini,
Michael V. Maseda,
Tim B. Miller,
Abby Mintz,
Ikki Mitsuhashi,
Themiya Nanayakkara,
Erica Nelson,
Richard Pan,
Natalia Porraz Barrera,
Bingjie Wang
, et al. (3 additional authors not shown)
Abstract:
We constrain the nebular attenuation curve and investigate dust geometry in star-forming galaxies at cosmic noon using photometric medium-band emission line measurements. We measure H-alpha emission line fluxes for a sample of 209 star-forming galaxies at 1.2<z<2.4 in MegaScience/UNCOVER with stellar masses spanning $7.85<\log_{10}(M_*/M_\odot)<11.0$. For 66 of these galaxies, we also measure a Pa…
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We constrain the nebular attenuation curve and investigate dust geometry in star-forming galaxies at cosmic noon using photometric medium-band emission line measurements. We measure H-alpha emission line fluxes for a sample of 209 star-forming galaxies at 1.2<z<2.4 in MegaScience/UNCOVER with stellar masses spanning $7.85<\log_{10}(M_*/M_\odot)<11.0$. For 66 of these galaxies, we also measure a Pa-beta flux. We find that the Pa-beta/H-alpha line ratio increases strongly with stellar mass and star-formation rate (SFR) across our full mass range, indicating that more massive galaxies are dustier. We compare our results with a mass-, SFR-, and redshift-matched sample of galaxies from the MOSDEF survey with spectroscopic measurements of H-alpha/H-beta, finding that a shallow Reddy et al. (2025) nebular attenuation curve is more consistent with our observations than the typically assumed Cardelli et al. (1989) attenuation curve, especially for massive galaxies. This shallow attenuation curve could be explained by low dust covering fractions in star-forming regions. Through comparison to other studies, we show that assuming this shallower attenuation curve can increase the inferred A_Halpha,neb by up to 1 magnitude at high masses. We observe no trend between A_Halpha,neb and axis ratio, indicating that nebular attenuation is likely localized to small clumps. Altogether, our results strongly suggest that dust geometry is patchy and non-uniform, especially in massive galaxies. Our results highlight the ability of JWST medium bands to probe emission lines for large samples of galaxies, and statistically constrain dust properties in upcoming large programs.
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Submitted 11 February, 2026;
originally announced February 2026.
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It's More Complicated Than You Think: A Forward Model to Infer the Recent Star Formation History, Bursty or Not, of Galaxy Populations
Authors:
Emilie Burnham,
Bingjie Wang,
Joel Leja,
Owen Gonzales,
Jenny E. Greene,
Kartheik G. Iyer,
Abby Mintz,
David J. Setton,
Sarah Wellons,
Rachel Bezanson,
Olivia Curtis,
Robert Feldmann,
Tim B. Miller,
Themiya Nanayakkara,
Joshua S. Speagle,
Katherine A. Suess,
Guochao Sun
Abstract:
Observations of the early Universe (z > 4) with the James Webb Space Telescope reveal galaxy populations with a wide range of intrinsic luminosities and colors. Bursty star formation histories (SFHs), characterized by short-term fluctuations in the star formation rate (SFR), may explain this diversity, but constraining burst timescales and amplitudes in individual galaxies is challenging due to de…
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Observations of the early Universe (z > 4) with the James Webb Space Telescope reveal galaxy populations with a wide range of intrinsic luminosities and colors. Bursty star formation histories (SFHs), characterized by short-term fluctuations in the star formation rate (SFR), may explain this diversity, but constraining burst timescales and amplitudes in individual galaxies is challenging due to degeneracies and sensitivity limits. We introduce a population-level simulation-based inference framework that recovers the power and timescales of SFR fluctuations by forward-modeling galaxy populations and distributions of rest-UV to rest-optical spectral features sensitive to star formation timescales. We adopt a stochastic SFH model based on a power spectral density formalism spanning 1 Myr-10 Gyr. Using simulated samples of N=500 galaxies at z~4 with typical JWST/NIRSpec uncertainties, we demonstrate that: (i) the power of SFR fluctuations can be measured with sufficient precision to distinguish between simulations (e.g., FIRE-2-like vs. Illustris-like populations at >99% confidence for timescales < 100 Myr); (ii) simultaneously modeling stochastic fluctuations and the recent (t_L < 500 Myr) average SFH slope is essential, as secular trends otherwise mimic burstiness in common diagnostics; (iii) frequent, intense bursts impose an outshining limit, and bias inference toward underestimating burstiness due to the obscuration of long-timescale power; and (iv) the power of SFR fluctuations can be inferred to 95% confidence across all timescales in both smooth and bursty populations. This framework establishes a novel and robust method for placing quantitative constraints on the feedback physics regulating star formation using large, uniformly selected spectroscopic samples.
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Submitted 28 January, 2026;
originally announced January 2026.
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UNCOVER/MegaScience Finds Uniform and Highly Bursty Star Formation at 3 < z < 9, consistent with the High-Redshift UV Luminosity Function
Authors:
Ikki Mitsuhashi,
Katherine A. Suess,
Joel Leja,
Rachel Bezanson,
Jenny E. Greene,
Emilie Burnham,
Gourav Khullar,
Abby Mintz,
Themiya Nanayakkara,
Karl Glazebrook,
Sedona H. Price,
David J. Setton,
Bingjie Wang,
John R. Weaver,
Hakim Atek,
Pratika Dayal,
Robert Feldmann,
Seiji Fujimoto,
Lukas J. Furtak,
Brian Lorenz,
Natalia Porraz Barrera,
Ivo Labbe,
Gabriel Brammer,
Sam E. Cutler,
Richard Pan
, et al. (2 additional authors not shown)
Abstract:
Star formation timescales are key to understanding fundamental physics like feedback mechanisms, as well as the abundance of bright galaxies at $z>10$. We investigate galaxy star formation histories (SFHs) and their evolution across $z\sim3$--9 by measuring the line-to-UV ratio (\rline) and line equivalent width (EW) of \hanii\ and \oiiihb\ directly from UNCOVER/MegaScience spectro-photometry with…
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Star formation timescales are key to understanding fundamental physics like feedback mechanisms, as well as the abundance of bright galaxies at $z>10$. We investigate galaxy star formation histories (SFHs) and their evolution across $z\sim3$--9 by measuring the line-to-UV ratio (\rline) and line equivalent width (EW) of \hanii\ and \oiiihb\ directly from UNCOVER/MegaScience spectro-photometry without relying on a specific SFH or nebular line modeling. Our photometric measurements recover \rline\ and EW to $<10\%$ systematic accuracy compared to spectroscopy. This allows us to construct a large mass- (and flux-) complete sample and quantitatively examine how \rline\ evolves with redshift and stellar mass. We find that the intrinsic scatter in \rline\ does not significantly evolve with redshift across $3<z<7$, though it may increase at $z\gtrsim8$. We build population-level toy models using \texttt{fsps} to help interpret our observations, and find that scatter in \rline\ primarily reflects the amplitude of SFH fluctuations; this implies that our observed lack of evolution in the scatter of \rline\ is due to similar star formation burstiness from $z\sim3$ to $z\sim7$. Our observations are best reproduced by a set of SFHs with rising, long-duration, and large-amplitude bursts. Finally, we demonstrate that the toy model that best describes our $z\sim6$ data can boost UV brightness by up to $ΔM_{\rm UV}\sim-2.0\,{\rm mag}$ compared with a 200\,Myr constant SFH, and naturally produces a large number of galaxies at $z>10$. This suggests that no significant evolution in star formation burstiness is required to explain the abundance of UV-bright galaxies at high redshift.
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Submitted 22 January, 2026;
originally announced January 2026.
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The Merian Survey: A Statistical Census of Bright Satellites of Milky Way Analogs
Authors:
Yue Pan,
Shany Danieli,
Jenny E. Greene,
Jiaxuan Li,
Alexie Leauthaud,
Erin Kado-Fong,
Yifei Luo,
Abby Mintz,
Alyson Brooks,
Song Huang,
Annika H. G. Peter,
Joy Bhattacharyya,
Lee S. Kelvin
Abstract:
We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection -- including magnit…
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We present a statistical census of bright, star-forming satellite galaxies around Milky Way (MW) analogs using the first data release of the Merian Survey. Our sample consists of 393 MW analogs with stellar masses $10^{10.5} < M_{\star, \rm host} < 10^{10.9} M_\odot$ at redshifts $0.07 < z < 0.09$, all central galaxies of their own dark matter halos. Using photometric selection -- including magnitude, color, angular size, photometric redshift, and size-mass cuts -- we identify 793 satellite candidates around these 393 hosts. Our selection leverages two medium-band filters targeting H$α$ and [O \textsc{iii}] emission, enabling a nearly complete sample of star-forming, Magellanic Clouds-like satellites with $M_{\star, \rm sat} \gtrsim 10^{8} M_\odot$. We find that $\sim80\%$ of hosts have 0-3 massive satellites, and $13\pm4\%$ have two satellites (similar to the MW). Satellite abundance correlates with total stellar mass, and we provide significantly improved statistics for the most massive satellites at $\log_{10}[M_{\star, \rm sat}/M_{\odot}] \gtrsim 10$. The completeness-corrected radial distribution is less centrally concentrated than an NFW profile. In contrast, the Milky Way satellites are more centrally concentrated than the 50\% richest Merian systems, but are broadly consistent with the 50\% most centrally concentrated Merian systems. Our results highlight the power of medium-band photometry for satellite identification and provide a key benchmark for studying satellite quenching, environmental effects, and hierarchical galaxy formation.
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Submitted 14 December, 2025;
originally announced December 2025.
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Machine Learning Integrated Near-Infrared Surface-Enhanced Raman Spectroscopy for Accurate Strain-Level Virus Identification
Authors:
Na Zhang,
Ziyang Wang,
Xielin Wang,
Gabriel A. Vázquez-Lizardi,
Paula Piñeiro Varela,
Dorleta Jimenez de Aberasturi,
David E. Sanchez,
Nestor Perea-Lopez,
Samuel Lin,
Ryeanne Ricker,
Edgar Dimitrov,
Alexander J. Sredenschek,
Kalana D. Halanayake,
Yin-Ting Yeh,
Julian A. Mintz,
Jiarong Ye,
Sharon Xiaolei Huang,
Huaguang Lu,
Elodie Ghedin,
Danielle Reifsnyder Hickey,
Luis M. Liz-Marzán,
Shengxi Huang,
Mauricio Terrones
Abstract:
Strain-level identification of viruses is critical for effective public health responses to potential outbreaks, yet current diagnostic methods often lack the necessary speed or sensitivity. Surface-enhanced Raman spectroscopy (SERS) offers great potential for fast and precise virus clarification through unique vibrational fingerprints of biological components. However, existing protocols typicall…
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Strain-level identification of viruses is critical for effective public health responses to potential outbreaks, yet current diagnostic methods often lack the necessary speed or sensitivity. Surface-enhanced Raman spectroscopy (SERS) offers great potential for fast and precise virus clarification through unique vibrational fingerprints of biological components. However, existing protocols typically operate outside of the tissue's transparent near-infrared (NIR) window, and are further limited by the intrinsic complexity of clinical viral samples, which complicates spectral analysis and recognition. Here, we report an artificial intelligence (AI)-empowered NIR-SERS platform that integrates machine learning with a rationally designed hybrid substrate: gold nanostars (AuNSt) coupled with gold-coated carbon nanotube arrays (AuCNT). This architecture generates highly localized plasmonic hot spots resonant tuned to NIR excitation, as confirmed by electron energy-loss spectroscopy (EELS), enabling effective signal amplification from viral components. Our system and protocols provide accurate classification of respiratory viruses, including influenza viruses and coronaviruses, not only at the type and subtype levels, but also the more challenging strain level. This approach overcomes the plasmonic mismatch in conventional SERS and the lack of generalizability in AI-driven diagnostics. It shows promise for enhancing rapid virus detection and identification of novel strains and outbreak response capabilities, thus potentially addressing critical challenges in global public health preparedness.
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Submitted 11 September, 2025;
originally announced September 2025.
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Taking a Break at Cosmic Noon: Continuum-selected Low-mass Galaxies Require Long Burst Cycles
Authors:
Abby Mintz,
David J. Setton,
Jenny E. Greene,
Joel Leja,
Bingjie Wang,
Emilie Burnham,
Katherine A. Suess,
Hakim Atek,
Rachel Bezanson,
Gabriel Brammer,
Sam E. Cutler,
Pratika Dayal,
Robert Feldmann,
Lukas J. Furtak,
Karl Glazebrook,
Gourav Khullar,
Vasily Kokorev,
Ivo Labbé,
Jorryt Matthee,
Michael V. Maseda,
Tim B. Miller,
Ikki Mitsuhashi,
Themiya Nanayakkara,
Richard Pan,
Sedona H. Price
, et al. (3 additional authors not shown)
Abstract:
While bursty star formation in low-mass galaxies has been observed in local populations and reproduced in simulations, the dormant phase of the burst cycle has not been well studied beyond the local Universe due to observational limitations. We present a unique sample of 43 JWST PRISM spectra of low-mass galaxies ($M_\star < 10^{9.5}\,M_\odot$) at cosmic noon ($1<z<3$), uniformly selected on F200W…
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While bursty star formation in low-mass galaxies has been observed in local populations and reproduced in simulations, the dormant phase of the burst cycle has not been well studied beyond the local Universe due to observational limitations. We present a unique sample of 43 JWST PRISM spectra of low-mass galaxies ($M_\star < 10^{9.5}\,M_\odot$) at cosmic noon ($1<z<3$), uniformly selected on F200W magnitude and precise photometric redshifts enabled by 20-band JWST photometry from the UNCOVER and MegaScience surveys. The spectra reveal numerous strong Balmer breaks, which are negatively correlated with the galaxies' H$α$ equivalent width. By comparing these observations to synthetic samples of spectra generated using a simple parametrization of bursty star formation histories, we show that star formation in low-mass galaxies at cosmic noon is likely dominated by burst cycles with long timescales ($\gtrsim 100$ Myr) and large deviations below the star-forming main sequence ($\gtrsim 0.8$ dex). Our results suggest that galaxies in this population--at least those within our detection limits--should not be classified solely by their current star formation rates, but instead viewed as a unified population undergoing dynamic movement above and below the star-forming main sequence. The derived constraints demonstrate that long-timescale fluctuations are important for this class of galaxies, indicating that galaxy-scale gas cycles--rather than molecular-cloud-scale stochasticity--are the primary regulators of star formation variability in low-mass galaxies at cosmic noon.
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Submitted 10 March, 2026; v1 submitted 19 June, 2025;
originally announced June 2025.
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Measuring Emission Lines with JWST-MegaScience Medium-Bands: A New Window into Dust and Star Formation at Cosmic Noon
Authors:
Brian Lorenz,
Katherine A. Suess,
Mariska Kriek,
Sedona H. Price,
Joel Leja,
Erica Nelson,
Hakim Atek,
Rachel Bezanson,
Gabriel Brammer,
Sam E. Cutler,
Pratika Dayal,
Anna de Graaff,
Jenny E. Greene,
Lukas J. Furtak,
Ivo Labbé,
Danilo Marchesini,
Michael V. Maseda,
Tim B. Miller,
Abby Mintz,
Ikki Mitsuhashi,
Richard Pan,
Natalia Porraz Barrera,
Bingjie Wang,
John R. Weaver,
Christina C. Williams
, et al. (1 additional authors not shown)
Abstract:
We demonstrate the power of JWST-NIRCam medium-band photometry to measure emission line fluxes and study dust and star formation properties of galaxies at cosmic noon. In this work, we present photometric emission line measurements and spatially-resolved maps of H$α$ and Pa$β$ for a sample of 14 galaxies at $1.3\leq z\leq 2.4$, observed by the MegaScience medium-band survey and the UNCOVER deep sp…
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We demonstrate the power of JWST-NIRCam medium-band photometry to measure emission line fluxes and study dust and star formation properties of galaxies at cosmic noon. In this work, we present photometric emission line measurements and spatially-resolved maps of H$α$ and Pa$β$ for a sample of 14 galaxies at $1.3\leq z\leq 2.4$, observed by the MegaScience medium-band survey and the UNCOVER deep spectroscopic survey. We measure line fluxes directly from the medium-band photometry and compare with spectroscopic measurements from UNCOVER. We find reasonable agreement between the photometric and spectroscopic emission line fluxes for both H$α$ and Pa$β$, with scatter $<0.15$ dex down to emission line equivalent widths of $10$Å. We also make a nebular dust measurement from the ratio Pa$β$ / H$α$, finding an average nebular A$_\mathrm{V}$ of 1.4. Our photometric A$_\mathrm{V}$ measurements show a slightly larger scatter of $0.5$ magnitudes when compared to spectroscopic measurements; however, this scatter may be partially caused by aperture effects. Finally, we produce spatially resolved maps of H$α$ emission, Pa$β$ emission, and stellar continuum. We find that offsets in H$α$ and Pa$β$ emission are common, especially for galaxies with the highest A$_\mathrm{V}$, indicating dusty sub-structures. Furthermore, the correlation between H$α$ and continuum emission decreases with increasing A$_\mathrm{V}$, suggesting that the dustiest objects have clumpy dust and star formation distributions. Our study demonstrates the power of medium-band photometry to directly probe emission line strengths, star formation, and dust attenuation for hundreds of galaxies in UNCOVER and thousands of galaxies in upcoming JWST medium-band surveys.
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Submitted 15 May, 2025;
originally announced May 2025.
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A Spectroscopic Survey of Metal-Poor OB Stars in Local Dwarf Galaxy NGC 3109
Authors:
Abby Mintz,
O. Grace Telford,
Evan N. Kirby,
John Chisholm,
Kristen B. W. McQuinn,
Danielle Berg
Abstract:
As JWST uncovers increasingly strong evidence that metal-poor, massive stars in early galaxies dominated reionization, observational constraints on the properties of such stars are more relevant than ever before. However, spectra of individual O- and B-type stars are rare at the relevant metallicities ($\lesssim 0.2$ $Z_\odot$), leaving models of stellar evolution and ionizing flux poorly constrai…
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As JWST uncovers increasingly strong evidence that metal-poor, massive stars in early galaxies dominated reionization, observational constraints on the properties of such stars are more relevant than ever before. However, spectra of individual O- and B-type stars are rare at the relevant metallicities ($\lesssim 0.2$ $Z_\odot$), leaving models of stellar evolution and ionizing flux poorly constrained by data in this regime. We present new medium-resolution ($R\sim 4000)$ Keck/DEIMOS optical spectra of 17 OB stars in the local low-metallicity ($0.12$ $Z_\odot$) dwarf galaxy NGC 3109. We assign spectral types to the stars and present new criteria for selecting O stars using optical and NUV photometry from Hubble Space Telescope imaging. We fit the spectra and photometry with grids of stellar atmosphere models to measure stellar temperatures, surface gravities, luminosities, radii, and masses. We find evidence of strong mass loss via radiation-driven stellar winds in two O stars, one of which is the hottest, youngest, and most massive star confirmed in the host galaxy to date. Though its spectrum does not meet conventional Wolf-Rayet spectral classification criteria, this metal-poor O If star produces strong He II 4686 emission and its evolutionary status is ambiguous. This work nearly doubles the number of OB stars with measured parameters in NGC 3109, including ten stars with no previously reported parameters, four with no published spectroscopy, and four binary candidates. This large sample of OB stellar parameters provides a new observational testbed to constrain the stellar astrophysics that drove cosmic reionization and influenced the evolution of the earliest galaxies.
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Submitted 24 March, 2025;
originally announced March 2025.
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A Nonparametric Morphological Analysis of H$α$ Emission in Bright Dwarfs Using the Merian Survey
Authors:
Abby Mintz,
Jenny E. Greene,
Erin Kado-Fong,
Shany Danieli,
Jiaxuan Li,
Yifei Luo,
Alexie Leauthaud,
Vivienne Baldassare,
Song Huang,
Annika H. G. Peter,
Joy Bhattacharyya,
Mingyu Li,
Yue Pan
Abstract:
Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of H$α$ emission maps and stellar continua for a sample of galaxies with $8\lesssim\log (M_\star/M_\odot) < 10.3$ at $0.064<z<0.1$. We present a novel method for estimating the stellar continuum emission through the Merian Survey's N708 medium-band filter, which we use to measure H…
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Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of H$α$ emission maps and stellar continua for a sample of galaxies with $8\lesssim\log (M_\star/M_\odot) < 10.3$ at $0.064<z<0.1$. We present a novel method for estimating the stellar continuum emission through the Merian Survey's N708 medium-band filter, which we use to measure H$α$ emission and produce H$α$ maps for our sample of galaxies with seven-band Merian photometry and available spectroscopy. We measure nonparametric morphological statistics for the H$α$ and stellar continuum images, explore how the morphology of the H$α$ differs from the continuum, and investigate how the parameters evolve with the galaxies' physical properties. In agreement with previous results for more massive galaxies, we find that the asymmetry of the stellar continuum increases with specific star formation rate (SSFR) and we extend the trend to lower masses, also showing that it holds for the asymmetry of the H$α$ emission. We find that the lowest-mass galaxies with the highest SSFR have H$α$ emission that is consistently heterogeneous and compact, while the less active galaxies in this mass range have H$α$ emission that appears diffuse. At higher masses, our data do not span a sufficient range in SSFR to evaluate whether similar trends apply. We conclude that high SSFRs in low-mass galaxies likely result from dynamical instabilities that compress a galaxy's molecular gas to a dense region near the center.
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Submitted 2 October, 2024;
originally announced October 2024.
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Merian: A Wide-Field Imaging Survey of Dwarf Galaxies at z~0.06-0.10
Authors:
Shany Danieli,
Erin Kado-Fong,
Song Huang,
Yifei Luo,
Ting S Li,
Lee S Kelvin,
Alexie Leauthaud,
Jenny E. Greene,
Abby Mintz,
Xiaojing Lin,
Jiaxuan Li,
Vivienne Baldassare,
Arka Banerjee,
Joy Bhattacharyya,
Diana Blanco,
Alyson Brooks,
Zheng Cai,
Xinjun Chen,
Akaxia Cruz,
Robel Geda,
Runquan Guan,
Sean Johnson,
Arun Kannawadi,
Stacy Y. Kim,
Mingyu Li
, et al. (10 additional authors not shown)
Abstract:
We present the Merian Survey, an optical imaging survey optimized for studying the physical properties of bright star-forming dwarf galaxies. Merian is carried out with two medium-band filters ($N708$ and $N540$, centered at $708$ and $540$ nm), custom-built for the Dark Energy Camera (DECam) on the Blanco telescope. Merian covers $\sim 750\,\mathrm{deg}^2$ of equatorial fields, overlapping with t…
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We present the Merian Survey, an optical imaging survey optimized for studying the physical properties of bright star-forming dwarf galaxies. Merian is carried out with two medium-band filters ($N708$ and $N540$, centered at $708$ and $540$ nm), custom-built for the Dark Energy Camera (DECam) on the Blanco telescope. Merian covers $\sim 750\,\mathrm{deg}^2$ of equatorial fields, overlapping with the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) wide, deep, and ultra-deep fields. When combined with the HSC-SSP imaging data ($grizy$), the new Merian DECam medium-band imaging allows for photometric redshift measurements via the detection of H$\rmα$ and [OIII] line emission flux excess in the $N708$ and $N540$ filters, respectively, at $0.06<z<0.10$. We present an overview of the survey design, observations taken to date, data reduction using the LSST Science Pipelines, including aperture-matched photometry for accurate galaxy colors, and a description of the data included in the first data release (DR1). The key science goals of Merian include: probing the dark matter halos of dwarf galaxies out to their virial radii using high signal-to-noise weak lensing profile measurements, decoupling the effects of baryonic processes from dark matter, and understanding the role of black holes in dwarf galaxy evolution. This rich dataset will also offer unique opportunities for studying extremely metal-poor galaxies via their strong [OIII] emission and H$\rmα$ lines, as well as [OIII] emitters at $z\sim 0.4$, and Ly$\rmα$ emitters at $z\sim 3.3$ and $z\sim 4.8$. Merian showcases the power of utilizing narrow and medium-band filters alongside broad-band filters for sky imaging, demonstrating their synergistic capacity to unveil astrophysical insights across diverse astrophysical phenomena.
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Submitted 8 October, 2024; v1 submitted 2 October, 2024;
originally announced October 2024.
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The Merian Survey: Design, Construction, and Characterization of a Filter Set Optimized to Find Dwarf Galaxies and Measure their Dark Matter Halo Properties with Weak Lensing
Authors:
Yifei Luo,
Alexie Leauthaud,
Jenny Greene,
Song Huang,
Erin Kado-Fong,
Shany Danieli,
Ting S. Li,
Jiaxuan Li,
Diana Blanco,
Erik J. Wasleske,
Joseph Wick,
Abby Mintz,
Runquan Guan,
Annika H. G. Peter,
Vivienne Baldassare,
Alyson Brooks,
Arka Banerjee,
Joy Bhattacharyya,
Zheng Cai,
Xinjun Chen,
Jim Gunn,
Sean D. Johnson,
Lee S. Kelvin,
Mingyu Li,
Xiaojing Lin
, et al. (6 additional authors not shown)
Abstract:
The Merian survey is mapping $\sim$ 850 degrees$^2$ of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the desig…
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The Merian survey is mapping $\sim$ 850 degrees$^2$ of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 ($λ_c = 7080 \unicode{x212B}$, $Δλ= 275\unicode{x212B}$) and N540 ($λ_c = 5400\unicode{x212B}$, $Δλ= 210\unicode{x212B}$). The central wavelengths and filter widths of N708 and N540 were designed to detect the $\rm Hα$ and $\rm [OIII]$ emission lines of galaxies in the mass range $8<\rm \log M_*/M_\odot<9$ by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of $\sim$ 85,000 star-forming dwarf galaxies with a photometric redshift accuracy of $σ_{Δz/(1+z)}\sim 0.01$ and an outlier fraction of $η=2.8\%$ over the redshift range $0.058<z<0.10$. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing $\rm S/N \sim 32$ within $r<0.5$ Mpc and lensing $\rm S/N \sim 90$ within $r<1.0$ Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies.
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Submitted 3 April, 2024; v1 submitted 30 May, 2023;
originally announced May 2023.
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Constraining the Size of the Circumgalactic Medium Using the Transverse Autocorrelation Function of C IV Absorbers in Paired Quasar Spectra
Authors:
Abby Mintz,
Marc Rafelski,
Regina A. Jorgenson,
Michele Fumagalli,
Rajeshwari Dutta,
Crystal L. Martin,
Elisabeta Lusso,
Kate H. R. Rubin,
John M. O'Meara
Abstract:
The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium (IGM). In this study we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER…
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The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium (IGM). In this study we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift $2 < z < 3$. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.7" and 132.9" and projected physical separations ($r_\perp$) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of C IV ($λλ1548, 1550$) with equivalent widths ranging from 6 mÅ $\leq W_{r, 1550} \leq 2053$ mÅ. The best fit linear model to the log-space equivalent width frequency distribution ($\log f(W_r) = m\log(W_{r}) + b$) of the sample yields coefficients of $m=-1.44\pm0.16$ and $b=-0.43\pm0.16$. To constrain the projected extent of C IV, we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at low $r_\perp$ provides a lower limit for the coherence length of the metal enriched CGM - on the order of 200 $h^{-1}$ comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of C IV in the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies.
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Submitted 7 June, 2022;
originally announced June 2022.
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Testing Models of Triggered Star Formation with Young Stellar Objects in Cepheus OB4
Authors:
Abby Mintz,
Joseph L. Hora,
Elaine Winston
Abstract:
OB associations are home to newly formed massive stars, whose turbulent winds and ionizing flux create H II regions rich with star formation. Studying the distribution and abundance of young stellar objects (YSOs) in these ionized bubbles can provide essential insight into the physical processes that shape their formation, allowing us to test competing models of star formation. In this work, we ex…
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OB associations are home to newly formed massive stars, whose turbulent winds and ionizing flux create H II regions rich with star formation. Studying the distribution and abundance of young stellar objects (YSOs) in these ionized bubbles can provide essential insight into the physical processes that shape their formation, allowing us to test competing models of star formation. In this work, we examined one such OB association, Cepheus OB4 (Cep OB4) - a well-suited region for studying YSOs due to its Galactic location, proximity, and geometry. We created a photometric catalog from Spitzer/IRAC mosaics in bands 1 (3.6 $μ$m) and 2 (4.5 $μ$m). We supplemented the catalog with photometry from WISE, 2MASS, IRAC bands 3 (5.8 $μ$m) and 4 (8.0 $μ$m), MIPS 24 $μ$m, and MMIRS near IR data. We used color-color selections to identify 821 YSOs, which we classified using the IR slope of the YSOs' spectral energy distributions (SEDs), finding 67 Class I, 103 flat spectrum, 569 Class II, and 82 Class III YSOs. We conducted a clustering analysis of the Cep OB4 YSOs and fit their SEDs. We found many young Class I objects distributed in the surrounding shell and pillars as well as a relative age gradient of unclustered sources, with YSOs generally decreasing in age with distance from the central cluster. Both of these results indicate that the expansion of the H II region may have triggered star formation in Cep OB4.
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Submitted 7 October, 2021;
originally announced October 2021.
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On the Cayley semigroup of a finite aperiodic semigroup
Authors:
Avi Mintz
Abstract:
Let $S$ be a finite semigroup. In this paper we introduce the functions $φ_s:S^* \to S^*$, first defined by Rhodes, given by $φ_s([a_1,a_2 ,...,a_n]) = [sa_1,sa_1a_2,..., sa_1a_2 ... a_n]$. We show that if $S$ is a finite aperiodic semigroup, then the semigroup generated by the functions $\{φ_s\}_{s \in S}$ is finite and aperiodic.
Let $S$ be a finite semigroup. In this paper we introduce the functions $φ_s:S^* \to S^*$, first defined by Rhodes, given by $φ_s([a_1,a_2 ,...,a_n]) = [sa_1,sa_1a_2,..., sa_1a_2 ... a_n]$. We show that if $S$ is a finite aperiodic semigroup, then the semigroup generated by the functions $\{φ_s\}_{s \in S}$ is finite and aperiodic.
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Submitted 25 August, 2008;
originally announced August 2008.