arXiv subjects

Bahram Mobasher

Publications and source records attributed to Bahram Mobasher.

At least 19 recordsLinked to original sources

arXiv2026

The Roman eXtreme Deep Field (RXDF)

The Roman eXtreme Deep Field (RXDF) program is one of the five General Astrophysics Survey (GAS) programs approved for observing time with the Nancy Grace Roman Space Telescope in Cycles 1 and 2. It has been allocated 386.41 hours to carry out an imaging survey to AB = 30 mag (5-sigma) over ~140x larger area than the Hubble eXtreme Deep Field (HXDF) full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB = 30 mag in RZYJH, 29 mag in F, and 28 mag in K, over a full-depth area of 678.75 arcmin^2 embedded in a total area of 1,243 arcmin^2, and far exceeding the depths of the Roman Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field (EUDF) near the North Ecliptic Pole (NEP), a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive coverage from the James Webb Space Telescope (JWST) NEXUS Treasury program. The observations will cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time-domain studies on time baselines from ~10 days to over ~2 years. The RXDF is uniquely positioned to address critical questions in reionization, large scale structure (LSS), growth of supermassive black holes (SMBHs), little red dots (LRDs), and high-z supernovae (SNe); the volumes probed by HST+JWST are too small at these extreme depths, and even the deepest CCS tiers are too shallow. In addition to our key objectives, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy. This short document, which is converted from the approved RXDF proposal, aims to provide the community with a summary of the program.

astro-ph.GA↗

arXiv2026

Discovery of Very Minor Merger-Induced Star-forming Clumps at $z=3.33$ with JWST

High-redshift galaxies often contain ''clumps:'' compact, $\sim$kpc-scale regions of intense star formation. These substructures make up significant fractions of the masses and star-formation rates of their host galaxies and are expected to affect the morphologies of their hosts, such as by building up bulges. Studying clumps can therefore inform theoretical models of galaxy evolution. Two main mechanisms have been proposed for their formation: gas fragmentation from disk instabilities and compression of gas during gravitational interactions with other galaxies. In the latter, only mergers with mass ratios greater than 1:10 have been considered. Here, we report James Webb Space Telescope spectroscopy and imaging of JADES 1034862, a galaxy at $z_{\textrm{spec}} = 3.33$, which hosts a clump that formed during an interaction with a companion with a stellar mass that is $\approx28$ times lower than the host. From fits to the spectral energy distributions of the clump and the companion, it is found that both of their star-formation histories rose sharply in the most recent 100-300 Myr, during which the clump formed $\sim10^{7.2} \ M_{\odot}$ in stars and currently makes up $\approx10\%$ of the total star-formation rate of its host. Given the higher frequency of mergers with low mass ratios ($<1:10$) to those with higher ratios, we infer that a substantial fraction of high-redshift clumps could have formed through weak gravitational interactions.

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arXiv2026

Enhancing WISE Infrared Imaging to Spitzer Resolution Using Deep Learning Super-Resolution

We present a deep-learning framework that performs 4.6x spatial super-resolution from WISE W1 (3.4 micron) toward Spitzer IRAC Ch1 (3.6 micron), and characterize its behavior on the COSMOS field. We train on ~390,000 paired cutouts drawn uniformly within the WISE/Spitzer overlap and report all metrics on a held-out test set of 83,592 cutouts. The framework uses a convolutional neural network trained with a loss function that emphasizes accurate recovery of sources in crowded fields. The model recovers the total flux of the central source in a fixed aperture to a median relative error of 11%, a factor of ~2 better than the interpolation baselines; the gain reaches ~3x on the faintest quartile. The brightness dependence is monotonic: the aperture integrated flux error decreases from 13% on the faintest quartile to 8% on the brightest. At the 3-5 arcsec separations where WISE blends sources that Spitzer separates, the model recovers 35% of the source peaks detectable in the Spitzer truth compared with 9% for interpolation. The characteristic failure mode is oversmoothing of source profiles, which biases integrated flux measurements upward; this pattern is qualitatively similar to that of the interpolation baselines but is quantitatively smaller for the trained model. These results suggest genuine resolution enhancement and source deblending, providing a path toward applying super-resolution across the all-sky area that Spitzer could not cover. An appendix replicates the analysis at W2 -> IRAC Ch2 with consistent results; the trained model and code are publicly available.

astro-ph.IM↗

arXiv2026

The Galaxy's Guide to the Tokenizer: A Benchmark for Scientific Foundation Models

Tokenization is central to adapting scientific data for transformer-based foundation models, yet its impact on learned representations remains poorly understood. We compare four tokenization strategies, Affine, AIM, JetFormer, and VQ-VAE, within a unified transformer framework for astronomical imaging. Using 640,000 galaxy images from the DESI Legacy Survey and a shared AstroPT backbone, we evaluate each method on reconstruction fidelity and prediction of physical properties. Our results reveal trade-offs across approaches. The flow-based JetFormer achieves higher reconstruction quality, while VQ-VAE yields strong probe performance for galaxy physical properties. Affine and AIM better preserve localized morphological information. We find that reconstruction and representation quality are decoupled, and no single method consistently performs best across the tasks considered here. By grounding our evaluation in independently measured physical quantities, we hope this study serves to highlight the potential of scientific data as a basis for constructing interpretable benchmarks for foundation models.

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arXiv2026

Discovery and Analysis of a Type II Supernova Candidate at z = 3.19 from JWST's COSMOS-Web Survey

The launch of the James Webb Space Telescope (JWST) has enabled the discovery of a small but increasing sample of high-redshift core-collapse supernovae (CC SNe), which provide new tests of massive star evolution in the early Universe. In this study, we report the discovery of SN 2023aeaf in COSMOS-Web survey observations, which at $z = 3.195$ has one of the highest SN spectroscopic redshifts to date. Using two epochs of JWST photometry separated by $\sim$1 month in the rest frame, we photometrically classify SN 2023aeaf by comparing the JWST photometry to spectrophotometric CC SN and Type Ia (SN Ia) models and UV observations of SNe from the Swift telescope, finding that SN 2023aeaf is highly likely to be a Type II SN. A spectrum of the SN$+$host galaxy was also obtained $\sim$30 rest-frame days after discovery but shows no clearly identifiable SN features, with H$\alpha$ emission from the host potentially masking emission from the SN. Although the limited photometric coverage prevents strong constraints on the explosion properties, we find that the data are most consistent with a $\sim$12$M_\odot$ progenitor with $\sim$0.5$M_{\odot}$ of circumstellar material. We next use the host-galaxy spectrum and photometry to model the host spectral energy distribution (SED) using the Prospector Bayesian inference framework. We find that the host is a star-forming galaxy with a sSFR of $ \log_{10}(\rm sSFR/yr^{-1})= -10.17^{+0.13}_{-0.10}$, a stellar mass of $\log(M_\star/M_\odot) = 9.04^{+0.03}_{-0.04}$, and a gas-phase metallicity of $12 +{\rm log_{10}}({\rm O/H}) = 7.82\pm0.02$. SN 2023aeaf joins a growing sample of early Universe CC SNe with high luminosities, dense CSM, and low-metallicity environments.

astro-ph.HE↗

arXiv2026

Learning to See Sharper: A Physics-Informed Artificial Intelligence Framework for Super-Resolving Galaxy Spectra

The information recoverable from galaxy spectra depends fundamentally on spectral resolution, yet assembling large samples at high resolution remains observationally expensive. We present a deep-learning framework for spectral super-resolution that enhances low-resolution galaxy spectra by a factor of $\sim$10 in resolving power ($R\sim100$ to $R\sim1000$). The model is trained on 1,187 paired JWST/NIRSpec observations from the JADES program, where low-resolution prism spectra are matched with medium-resolution grating spectra (G140M, G235M, G395M) combined into a unified reference covering 1-5 $\mu$m. Our three-stage architecture performs an initial super-resolution, infers the redshift from the coarse reconstruction, and then applies a physics-informed residual refinement that uses attention across emission-line tokens to learn inter-line relationships and predict parametric line profiles, alongside a convolutional branch for continuum corrections. Evaluated on a 20% held-out sample, the model achieves noise-limited residuals over most of the spectral range and systematically improves the signal-to-noise ratio of key diagnostic lines including [OII], H$\beta$, [OIII], and H$\alpha$, often by factors of several. The super-resolved spectra successfully deblend features that are entirely unresolved at prism resolution, such as the [OIII] $\lambda\lambda4959,5007$ doublet and H$\beta$. As a proof of concept using JWST data, this approach is readily extensible to the low-resolution grism spectroscopy that will be delivered by Euclid and the Roman Space Telescope, potentially enabling population-level diagnostics across millions of galaxy spectra that would otherwise be inaccessible at grism resolution.

astro-ph.GA↗

arXiv2026

Optical Spectroscopy of Dwarf Galaxies at $z\sim 0.15$ in the COSMOS Field: Star Formation and Dust Properties

We present a spectroscopic study of low-mass galaxies (LMGs;$10^8\leq\rm M_*/M_\odot\leq10^9$) at $z\sim0.15$ in COSMOS field, and compare it to a control sample of intermediate-mass galaxies (IMGs;$10^9\leq\rm M_*/M_\odot\leq10^{10}$) at $z\sim0.35$. We examine their star formation rates (SFRs), dust attenuation properties, and the relationship between nebular and stellar reddening. For both samples, SFRs derived from H$\alpha$ are strongly correlated with SFRs from fitting simple star formation histories (SFHs) to the galaxies' spectral energy distributions. In fitting a joint SFR-$\rm M_*$ relation, we obtain a slope of $\rm {\Delta log(SFR_{H\alpha})}/{\Delta log(M_*/M_\odot)}=1.01\pm0.03$, indicating that fair ensembles of SFHs for galaxies at these stellar masses are well-described by scale-free, self-similar forms. We also examine their dust attenuation properties and the relationship between nebular and stellar reddening, exploring how these quantities vary with stellar mass and specific SFR (sSFR). Nebular attenuation increases with stellar mass for IMGs but is lower and less mass-dependent in LMGs, consistent with their reduced dust content. In all cases, stellar continuum attenuation is lower than nebular attenuation, as expected from the two-component dust model. The nebular-to-stellar color excess ratio in both samples is consistent with the canonical factor of 2.27. The ratio is mass-independent, but rises with sSFR in IMGs and remains constant in LMGs. These results suggest that in LMGs, efficient dispersal of birth clouds keeps the differential attenuation approximately constant across sSFR. Thus, although LMGs follow the same global SFR-$\rm M_*$ scaling as massive galaxies, their lower dust content and feedback-maintained ISM produce distinct attenuation behavior relative to IMGs.

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arXiv2026

A Morphology Catalog of Galaxies in CEERS: Evolution in the Size and Color Gradients of Galaxies Since Cosmic Dawn

We present measurements of morphological parameters from fitting 53,885 galaxies detected to a magnitude limit of F356W$< 28.5$ in the CEERS NIRCam imaging with galfit in six broadband filters: F115W, F150W, F200W, F277W, F356W, and F444W. We provide a public catalog of S\'ersic index, effective semi-major axis, axis ratio, integrated magnitude, and position angle for these galaxies in each of the filters. Uncertainties in the measured parameters are estimated from simulated galaxies that have similar noise and background properties as the observed galaxies. We compare our measurements with those in the CANDELS/EGS field measured with HST/WFC3 and find that the sizes agree to within 0.09 dex and the S\'ersic indices agree to within 0.13 dex. We further present the evolution in the size-mass relation, and find that the evolution to $z\sim9$ is consistent with previous results derived at lower redshift. Finally, we look at the color gradients of galaxies at $1 2.5$), the color gradients are nearly flat with no dependence on mass, indicating that the stellar populations are more uniform throughout. The structural measurements presented are accurate to $20\%$ or better for most galaxies with F356W $<27.0$ mag and will enable further studies of galaxy morphology to $z\sim10$.

astro-ph.GA↗

arXiv2026

FRESCO: Constraining Dust Attenuation and Star-Formation Rates of $z\sim 2$ Star-Forming Galaxies with JWST Paschen and Ground-Based Balmer Emission Line Observations

We present new constraints on dust attenuation and star-formation rates (SFRs) for 77 galaxies at redshifts $z=1.43-2.65$, using Paschen emission line detections from the JWST FRESCO survey and ground-based Balmer line measurements from the MOSDEF survey. Using nebular and continuum emission maps, we find that Paschen emission covers a smaller area than continuum emission observed in the F210M (2.1 $\mu$m; rest-frame optical) and F444W (4.4 $\mu$m; rest-frame near-IR) bands, and is preferentially located toward galaxy outskirts. These results suggest that current star formation is concentrated in regions farther from galaxy centers than older stellar populations traced by the continuum, indicative of inside-out star formation. With a careful accounting of slit-loss corrections for ground-based measurements, we calculate nebular reddening and dust-corrected SFRs using the Balmer decrement (H$\alpha$/H$\beta$) and Paschen-to-Balmer line ratios (Pa$\alpha$/H$\alpha$ and Pa$\beta$/H$\alpha$), assuming the Milky Way extinction curve. On average, Paschen-derived reddening and SFRs agree with Balmer-derived values; however, two galaxies exhibit significantly higher Paschen reddening and four show significantly higher Paschen SFRs. We find that non-unity dust covering fractions bias the Balmer decrement toward less reddened OB associations, while decrements involving the Paschen lines are less affected by this bias. These results highlight the enhanced sensitivity of the Paschen lines to the most heavily obscured OB associations in $z\sim2$ galaxies, particularly in galaxies with patchy dust geometries. Future studies using Paschen lines exclusively to measure nebular reddening will yield more robust constraints on the dustiest star-forming regions.

astro-ph.GA↗

arXiv2026

The ALPINE-CRISTAL-JWST Survey: Chemical Abundance Comparison Between the ISM and CGM of Main-Sequence Galaxies at z=4-6

Gaseous halos around galaxies play an important role in galaxy evolution. The exchange of metals from the interstellar medium (ISM) to the circumgalactic medium (CGM) are caused by the formation, feedback, and/or merging history of galaxies. We study the variation in chemical composition between the ISM ($\lesssim3\,$kpc) and CGM ($\sim5-10\,$kpc) for a sample of $M_{\star}>10^{9.5}\,M_{\odot}$ main-sequence galaxies at $4<z<6$ with both JWST and ALMA observations. Using JWST/NIRSpec integral field spectroscopy, we derive the optical line ratios from the ISM and the CGM for our sample focusing on the typical optical lines used for metallicity studies. Our comparison shows that the ISM and the CGM have similar chemical abundances. This indicates that the CGM of these typical $4<z<6$ galaxies is enriched to the level of their ISM in the early universe. Using statistical tests, we find that some of the line ratios show marginal differences between the ISM and CGM. Combined with \texttt{Cloudy} modeling, our results suggest that a difference in ionization level (higher for the ISM) is the dominant reason for the observed ratio difference of oxygen line ratios. There is also indication of a deficit in the nitrogen abundance with respect to oxygen in the CGM, which suggests a delay in redistribution of secondary nitrogen. Finally, an enhanced $F_{[\rm CII]\rm 158\mu m}/F_{\rm H\alpha}$ ratio is observed in the CGM, suggesting that feedback and/or mergers play a key role in metal mixing.

astro-ph.GA↗

arXiv2026

An ultra-high-resolution map of (dark) matter

Ordinary matter-including particles such as protons and neutrons-accounts for only about one sixth of all matter in the Universe. The rest is dark matter, which does not emit or absorb light but plays a fundamental role in galaxy and structure evolution. Because it interacts only through gravity, one of the most direct probes is weak gravitational lensing: the deflection of light from distant galaxies by intervening mass. Here we present an extremely detailed, wide-area weak-lensing mass map, covering 0.77 deg x 0.70 deg, using high-resolution imaging from the James Webb Space Telescope (JWST) as part of the COSMOS-Web survey. By measuring the shapes of 129 galaxies per square arcminute-many independently in the F115W and F150W bands-we achieve an angular resolution of 1.00 +/- 0.01 arcmin. Our map has more than twice the resolution of earlier Hubble Space Telescope maps, revealing how dark and luminous matter co-evolve across filaments, clusters, and under-densities. It traces mass features out to z ~ 2, including the most distant structure at z ~ 1.1. The sensitivity to high-redshift lensing constrains galaxy environments at the peak of cosmic star formation and sets a high-resolution benchmark for testing theories about the nature of dark matter and the formation of large-scale cosmic structure

astro-ph.CO↗

arXiv2025

Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to $z \sim 7$ with the Largest JWST Survey

We present a reconstruction of the large-scale structure using the James Webb Space Telescope's (JWST) COSMOS-Web program to trace environmentally driven galaxy evolution up to $z\sim7$. We applied a weighted kernel density estimation method to 160,000 galaxies with robust photometric redshifts. We find that stellar mass has a positive correlation with density at all redshifts, stronger for quiescent galaxies (QGs) at $z\lesssim2.5$, while at higher redshifts ($2.5\lesssim z\lesssim5.5$) this trend is confined to extreme overdense environments, consistent with early mass assembly in proto-clusters. The star-formation rate (SFR) shows a negative trend with density for QGs at $z\lesssim1.2$, reversing at $z\gtrsim1.8$, while star-forming galaxies (SFGs) show a mild positive correlation up to $z\sim5.5$. The specific SFR remains nearly flat for SFGs and declines with density for QGs at $z\lesssim1.2$. Moreover, mass and environmental quenching efficiencies show that mass-driven processes dominate at $z\gtrsim2.5$, the two processes act with comparable strength between $0.8\lesssim z\lesssim2.5$, and environmental quenching becomes stronger for low-mass galaxies ($M_\star\lesssim10^{10} M_\odot$) at $z\lesssim0.8$. These findings reveal that large-scale structure drives galaxy evolution by enhancing early mass assembly in dense regions and increasingly suppressing star formation in low-mass systems at later times, establishing the environmental role of the cosmic web across cosmic history. COSMOS-Web, the largest JWST survey, provides accurate and deep photometric redshifts, reaching 80% mass completeness at $\log(M_\star/M_\odot)\sim8.7$ at $z\sim7$, enabling the first view of how environments shaped galaxy evolution from the epoch of reionization to the present day.

astro-ph.GA↗

arXiv2025

The stellar mass function of quiescent and star-forming galaxies and its dependence on morphology in COSMOS-Web

We study the stellar mass function (SMF) of quiescent and star-forming galaxies and its dependence on morphology in 10 redshift bins at $0.2 0.6$) dominate the quiescent SMF at ${\rm log}(M_{\star}/{\rm M_{\odot}})>10$ at all redshifts, while disks ($B/T<0.2$) dominate at ${\rm log}(M_{\star}/{\rm M_{\odot}})<9$. However, most bulge-dominated galaxies are star-forming, with their fraction increasing with redshift and decreasing mass, consistent with being progenitors of quiescent bulges. We find evidence for environmental quenching onset at $z\sim3$ from the upturn in the quiescent SMF at ${\rm log}(M_{\star}/{\rm M_{\odot}})<9.5$, contributed by disk-dominated galaxies consistent with satellite quenching that retains disk morphologies. Number densities of ${\rm log}(M_{\star}/{\rm M_{\odot}})>10$ quiescent galaxies are lower than recent literature by $0.1-0.7$ dex, but agree well with simulations at $2 3$, simulations increasingly underpredict observations. Finally, we build an empirical model describing galaxy number density evolution by parametrizing quenching rates, baryon conversion efficiency, and bulge formation. Our model supports a scenario where star-forming galaxies grow central bulges before quenching in massive halos.

astro-ph.GA↗

arXiv2025

Searching Within Galaxies for the Earliest Signs of Quenching With Spatially Resolved Star Formation Histories in UVCANDELS Galaxies at z< 0.3

Understanding the complicated processes that regulate star formation and cause a galaxy to become quiescent is key to our comprehension of galaxy evolution. We used eight well resolved star-forming z$<$ 0.3 galaxies from the UVCANDELS survey, where a total of 10 HST bands including UV follow up in UVIS/F275W allow us to reconstruct the star formation histories (SFHs) of regions across each galaxy. This approach provides a powerful tool to explore the spatio-temporal connection between star formation and galaxy evolution. The spatial and temporal profiles of stellar mass and star formation rate surface density were obtained from the SFHs of these regions. We measure scaling relations and projected radial profiles of regions within each galaxy at the time of observation and at 1 Gyr lookback time, noting possible trends in the evolution. By comparing the change in star formation over time we can infer the timing and location of star formation and see early signs of star formation shut off before quenching occurs. We compared the star formation rate density -- stellar mass density scaling relations for individual galaxies as they evolve from 1 Gyr lookback time. The correlation lines pivot around a log-stellar mass surface density of 7.25 [$M_\odot$ $kpc^{-2}$] may be evidence of a self-regulating process on these scales. Radial profiles of galaxy Log sSFR show an overall decrease over 1 Gyr, but five galaxies show a greater change in Log sSFR at the outskirts than the center indicating a possible early onset of quenching in these galaxies.

astro-ph.GA↗

arXiv2025

The ALPINE-CRISTAL-JWST Survey: The Fast Metal Enrichment of Massive Galaxies at z~5

We present the stellar mass-metallicity relation (MZR) and mass-metallicity-star formation relation ("fundamental metallicity relation"; FMR) of 18 massive (log(M/Msun) = 9.5 - 11) main-sequence galaxies at z~5 from the ALPINE-CRISTAL-JWST sample. This sample complements recent studies by JWST at up to two orders of magnitude lower stellar masses. The metallicities are derived using strong optical lines, and verified by temperature-based oxygen abundance measurements for five galaxies for which faint auroral lines are detected. We find that the metal abundance evolves, on average, from 40% to 60% solar between z~5 and cosmic noon (z~2) at the massive end of the MZR, suggesting already significant metal enrichment at early times. The FMR at z=5 exhibits a 5x larger scatter (preferentially to lower metallicities) compared the local FMR relation. This scatter can be explained by a bursty star formation and the direct build-up of metals in early galaxies as well as differences in age and outflow efficiencies. Capitalizing on all available samples, we find that the observed MZR and FMR over three orders of stellar mass is generally in good agreement with results from cosmological simulation, although some underestimate the metal enrichment at low stellar masses. This may be due to too efficient metal-rich outflows. We show that the ALPINE-CRISTAL-JWST galaxies likely joined the current FMR at z~10 and will evolve into massive (log(M/Msun)~11.4) galaxies with super-solar metallicities by z=0.

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arXiv2025

Galaxy Zoo: Cosmic Dawn -- morphological classifications for over 41,000 galaxies in the Euclid Deep Field North from the Hawaii Two-0 Cosmic Dawn survey

We present morphological classifications of over 41,000 galaxies out to $z_{\rm phot}\sim2.5$ across six square degrees of the Euclid Deep Field North (EDFN) from the Hawaii Twenty Square Degree (H20) survey, a part of the wider Cosmic Dawn survey. Galaxy Zoo citizen scientists play a crucial role in the examination of large astronomical data sets through crowdsourced data mining of extragalactic imaging. This iteration, Galaxy Zoo: Cosmic Dawn (GZCD), saw tens of thousands of volunteers and the deep learning foundation model Zoobot collectively classify objects in ultra-deep multiband Hyper Suprime-Cam (HSC) imaging down to a depth of $m_{HSC-i} = 21.5$. Here, we present the details and general analysis of this iteration, including the use of Zoobot in an active learning cycle to improve both model performance and volunteer experience, as well as the discovery of 51 new gravitational lenses in the EDFN. We also announce the public data release of the classifications for over 45,000 subjects, including more than 41,000 galaxies (median $z_{\rm phot}$ of $0.42\pm0.23$), along with their associated image cutouts. This data set provides a valuable opportunity for follow-up imaging of objects in the EDFN as well as acting as a truth set for training deep learning models for application to ground-based surveys like that of the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) collaboration and the newly operational Vera C. Rubin Observatory.

astro-ph.GA↗

arXiv2025

Machine Learning Classification of COSMOS2020 Galaxies: Quiescent vs. Star-Forming

Accurately distinguishing between quiescent and star-forming galaxies is essential for understanding galaxy evolution. Traditional methods, such as spectral energy distribution (SED) fitting, can be computationally expensive and may struggle to capture complex galaxy properties. This study aims to develop a robust and efficient machine learning (ML) classification method to identify quiescent and star-forming galaxies within the Farmer COSMOS2020 catalog. We utilized JWST wide-field light cones from the Santa Cruz semi-analytical modeling framework to train a supervised ML model, the CatBoostClassifier, using 28 color features derived from 8 mutual photometric bands within the COSMOS catalog. The model was validated against a testing set and compared to the SED-fitting method in terms of precision, recall, F1-score, and execution time. Preprocessing steps included addressing missing data, injecting observational noise, and applying a magnitude cut (ch1 < 26 AB) along with a redshift range of 0.2 < z < 3.5 to align the simulated and observational datasets. The ML method achieved an F1-score of 89\% for quiescent galaxies, significantly outperforming the SED-fitting method, which achieved 54%. The ML model demonstrated superior recall (88% vs. 38%) while maintaining comparable precision. When applied to the COSMOS2020 catalog, the ML model predicted a systematically higher fraction of quiescent galaxies across all redshift bins within 0.2 < z < 3.5 compared to traditional methods like NUVrJ and SED-fitting. This study shows that ML, combined with multi-wavelength data, can effectively identify quiescent and star-forming galaxies, providing valuable insights into galaxy evolution. The trained classifier and full classification catalog are publicly available.

astro-ph.GA↗

arXiv2025

The Fraction of Clumpy Galaxies in JADES Over $2<z<9$

High-redshift galaxies exhibit compact regions of intense star formation, known as ``clumps,'' which are conspicuous in the rest-frame ultraviolet. Studying them can shed light on how they form and evolve and inform theoretical models of galaxy evolution. We examine the evolution of clumpy galaxies with redshift and stellar mass over ${2<z<9}$ with James Webb Space Telescope (JWST) imaging from the JWST Advanced Extragalactic Survey (JADES). Off-center clumps are detected in the rest-frame near-ultraviolet (NUV) using similar techniques to those in earlier studies based on Hubble Space Telescope (HST) images. This is done for a sample of 9,121 star-forming galaxies with stellar masses $\log\left(M_{\star}/M_{\odot}\right) \geq 8$. The fraction of clumpy galaxies, $f_{\rm{clumpy}}$, increases from ${\sim10\%}$ at ${z\sim7.75}$ to ${ \sim70\%}$ at $z\sim2.75$ at $\log\left(M_{\star}/M_{\odot}\right) \geq 9$. Our $f_{\rm{clumpy}}$ values are generally higher at fixed redshift and increase faster with decreasing redshift than what studies based on HST data found, which we attribute largely to the higher sensitivity of JWST. $f_{\rm{clumpy}}$ correlates with stellar mass. Our $f_{\rm{clumpy}}$ measurements are compared with those from simulations as well as other observations. At low redshifts ($z\lesssim5.75$) and intermediate-to-high stellar masses ($\log\left(M_{\star}/M_{\odot}\right) \geq 9$), our results suggest gas fragmentation due to violent disk instabilities to be the dominant mechanism for forming clumps. At high redshifts and intermediate stellar masses, compression of gas during mergers appears to dominate.

astro-ph.GA↗