Searcharxiv⌕ Search

arXiv subjects

Viraj Pandya

Publications and source records attributed to Viraj Pandya.

At least 19 recordsLinked to original sources
arXiv2026

Illuminating M82: Simulating X-ray Emission from Galactic Winds in a Starburst Galaxy

We generate mock X-ray observations from a suite of idealized high-resolution ($\sim 4$ pc), tall-box ($\sim 2 \times 2 \times 8$ kpc$^3$) simulations of star formation driven galactic winds in an M82-like system, varying the spatial resolution as well as the strength and distribution of supernova (SN) energy injection. We compare our mock X-ray observations with deep Chandra observations of the hot plasma around M82. While the simulated total X-ray luminosity, $L_X$, increases with resolution and when SNe feedback is spatially distributed, even in the best case scenario, our simulated $L_X$ is a factor of $\sim 50-100$ lower than observed and the surface brightness profiles of X-ray emission, $S_X(z)$, fall off too quickly with distance from the galaxy. Past results were able to reproduce these observables and we discuss potential simulation differences that could explain this discrepancy. We make the first comparison of the X-ray spectrum of our simulations to observations and find that our simulated spectrum is too soft, with a deficit of hard X-ray photons at $\gtrsim 1$ keV. We discuss how physical processes missing from our simulations and prior work (e.g., thermal conduction and cosmic rays) could help resolve this discrepancy.

astro-ph.GA↗
arXiv2026

TNG SAM: Bridging Hydrodynamical Complexity and Semi-Analytic Efficiency to Model Galaxy Formation

All cosmological models of galaxy formation must navigate the trade-off between physical accuracy and computational efficiency. Hydrodynamical simulations provide spatially resolved predictions for the co-evolution of dark matter, gas, stars, and black holes, but rely on phenomenological subgrid models for small-scale processes (e.g., star formation). Semi-analytic models (SAMs), by contrast, gain efficiency through simplified, analytic treatments of the same processes, at the cost of reduced predictive scope. In this work, we leverage the strengths of the Santa Cruz SAM and the IllustrisTNG hydrodynamical simulation to develop the TNG SAM. Calibrated to reproduce baryon cycling in stellar feedback-dominated TNG galaxies ($\sim 10^{10}M_\odot < M_{200} < 10^{12}M_\odot$), the TNG SAM introduces several key updates to the Santa Cruz framework regarding: 1) halo gas (re-)accretion efficiency, 2) a cooling model that moves beyond the traditional cold/hot mode dichotomy, 3) explicit treatment of both galactic- and halo-scale outflows, 4) star formation efficiency, and 5) the circulation of metals between galaxies and their surroundings. These changes enable the TNG SAM to reproduce TNG's flow of gas and metals from the scale of the galaxy to the halo, as well as global galaxy (e.g., stellar mass) and halo (e.g. hot halo gas mass) properties within $\lesssim 30\%$ accuracy out to $z=6$. This work demonstrates that, with appropriate calibration, SAMs can capture the complex physics of galaxy formation modeled in hydrodynamical simulations while providing a flexible framework for studying galaxy evolution across the large cosmological volumes targeted by future observational surveys.

astro-ph.GA↗
arXiv2026

Introducing sapphire: Towards Hybrid Physics-Informed, Data-Driven Modeling of Galaxy Formation

Semi-analytic models (SAMs) have been treating galaxy populations as dynamical systems for $\gtrsim50$ years, but their evolution equations remain poorly constrained. We introduce sapphire, a modular, automatically differentiable, GPU-accelerated SAM written in JAX. For the first time, we compute exact Jacobian and Hessian matrices of a galaxy formation SAM, using the Pandya et al. (2023) nonlinear differential equation system as an example. These allow efficient, interpretable local and global sensitivity analyses, which reveal that supernova energy loading is the key astrophysical parameter. We use gradient descent and Hamiltonian Monte Carlo (HMC) to perform comprehensive mock parameter recovery tests. These indicate that the $z=0$ stellar-to-halo-mass relation alone does not contain enough information to infer many astrophysical parameters. Using observations of star-forming galaxies from the MaNGA survey and the Behroozi et al. (2019) empirical model as one baseline, we derive multiple posteriors assuming different combinations of data, including $z=0$ interstellar medium gas fractions and metallicities. The inferred physical parameters suggest that galaxies self-regulate their star formation primarily through preventative rather than ejective feedback, though this remains uncertain due to the lack of satellite galaxies, black holes and multi-phase galactic atmosphere physics. Both Fisher and HMC forecasts demonstrate the potential of sapphire to enable precision inference for galaxy formation and cosmology in a hybrid physics-informed, data-driven way, but more work is needed to expand its library of models and methods. We make sapphire publicly available at https://github.com/virajpandya/sapphire.

astro-ph.GA↗
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↗
arXiv2025

The Cosmic Baryon Cycle in IllustrisTNG: flows of mass, energy, and metals

We measure and analyze the inflows and outflows of mass, energy, and metals through the interstellar medium (ISM) and circumgalactic medium (CGM) of galaxies in the IllustrisTNG100 simulations. We identify the dominant feedback mechanism in bins of halo virial mass and redshift by computing the integrated energy input from SNe and the ``kinetic'' and ``thermal'' mode of AGN feedback. We measure all quantities in a shell at the virial radius (``halo scale'') and one chosen to be approximately at the interface of the CGM and the interstellar medium (ISM; ``ISM scale''). We find that galaxies have strong net positive inflows on halo scales, and weaker but still net positive inflows on ISM scales, at $z\gtrsim 2$. At later times, partially due to the onset of kinetic AGN feedback in massive halos, inflows and outflows nearly balance one another, leading to the familiar effects of the slow-down of galaxy growth and the onset of quenching. Halos dominated by SN feedback show only weak evidence of preventative feedback on halo scales, and we see excess ISM scale accretion indicative of rapid gas recycling. Wind mass loadings decrease with increasing halo mass, and with increasing redshift, while energy loadings are nearly independent of both mass and redshift. The detailed catalogs of these mass, metal, and energy inflow and outflow rates on galaxy and halo scales can be used to guide empirical and semi-analytic models, and provide deeper insight into how galaxy growth and quenching is regulated in the IllustrisTNG simulations.

astro-ph.GA↗
arXiv2025

Impact of Cosmic Filaments on Galaxy Morphological Evolution and Predictions of Early Cosmic Web Structure for Roman

We leverage the IllustrisTNG cosmological simulations to test how the large-scale cosmic web shapes galaxy morphology and to forecast the early cosmic web structure that the Nancy Grace Roman Space Telescope will reveal. In the hydrodynamic TNG50 and $N$-body TNG50-Dark runs, we reconstruct the cosmic web at redshifts $z=0$, 0.5, 1, 2, 3, and 4 with the Monte Carlo Physarum Machine density estimator and the DisPerSE structure identification framework. We confirm that dark matter halos start out predominantly prolate (elongated) and their shapes are aligned with their nearest filaments; prolate galaxies retain strong shape-alignment with their outer halos to later times. The fraction of prolate galaxies and halos increases toward lower stellar mass, higher redshift, and lower-density filaments. Oblate and spheroidal galaxies show weaker trends with filament density, but spheroidal halos preferentially reside in higher-density filaments. We also find that higher-density filaments favor extended rotationally-supported disks, whereas lower-density filaments more often host smaller dispersion-supported systems. Then, generating mock galaxy samples from TNG100 and TNG50, we predict the early cosmic web accessible to Roman. We find that the spectroscopic emission-line depth planned for the High-Latitude Wide-Area Survey (HLWAS) yields a highly incomplete galaxy sample that does not accurately trace the $z=1$ cosmic web. A survey $\geq2.5\times$ deeper over a few square degrees would enable a proper reconstruction and reveal qualitatively correct filament-galaxy morphology relationships. Nevertheless, the planned HLWAS Deep field should still identify most galaxy overdensities; targeted deeper spectroscopy of these regions would efficiently and adequately map the early filamentary structure.

astro-ph.GA↗
arXiv2025

Second public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation

We describe the second data release (DR2) of the FIRE-2 cosmological zoom-in simulations of galaxy formation, from the Feedback In Realistic Environments (FIRE) project, available at http://flathub.flatironinstitute.org/fire. DR2 includes all snapshots for most simulations, starting at z ~ 99, with all snapshot time spacings <~ 25 Myr. The Core suite -- comprising 14 Milky Way-mass galaxies, 5 SMC/LMC-mass galaxies, and 4 lower-mass galaxies -- includes 601 snapshots to z = 0. For the Core suite, we also release resimulations with physics variations: (1) dark-matter-only versions; (2) a modified ultraviolet background with later reionization at z = 7.8; (3) magnetohydrodynamics, anisotropic conduction, and viscosity in gas; and (4) a model for cosmic-ray injection, transport, and feedback (assuming a constant diffusion coefficient). The Massive Halo suite now includes 8 massive galaxies with 278 snapshots to z = 1. The High Redshift suite includes 34 simulations: in addition to the 22 simulations run to z = 5, we now include 12 additional simulations run to z = 7 and z = 9. We also release 4 dark-matter-only cosmological boxes used to generate zoom-in initial conditions for many FIRE simulations. Most simulations include catalogs of (sub)halos and galaxies at all available snapshots, and most Core simulations to z = 0 include full halo merger trees.

astro-ph.GA↗
arXiv2025

Evaluating Mass Outflow Rate Estimators in FIRE-2 Simulations: Towards a Self-Consistent Framework for Spectral Line Based Predictions

$\require{mediawiki-texvc}$Galactic outflows shape galaxy evolution, but their mass, energy, and momentum transfer remain uncertain. High-resolution spectroscopy can help, but systematic discrepancies hinder model interpretation. In this study, we evaluate the performance of semi-analytical line transfer (SALT) and empirical partial covering models (PCMs) to recover the properties of outflows in the FIRE-2 simulation suite from synthetic Si II lines (1190 $\AA$, 1193 $\AA$, 1260 $\AA$, 1304 $\AA$, 1527 $\AA$). When applicable, we assess each model's ability to recover mass, energy, and momentum outflow rates, as well as radial density and velocity profiles, column densities, and flow geometries. We find that the PCM underestimates column densities by 1.3 dex on average in the range $15 < \log N\ [\text{cm}^{-2}] < 17$ with dispersion 1.3 dex. We attribute this bias to instrumental smoothing. Since the PCM underestimates column densities, it also underestimates flow rates, though its predictions are independent of radius, with a dispersion of 0.55 dex. We detect no bias in the SALT estimates of the column density with dispersion 1.3 dex. When the velocity and density field obey power laws, SALT can constrain the mass, momentum, and energy outflow rates to 0.36 (0.63), 0.56 (0.56), and 0.97 (0.80) dex at $0.15(0.30)R_{\text{vir}}$, respectively. However, certain profiles in FIRE-2 fall outside the SALT framework, where the model breaks down. We find that SALT effectively tracks the flow geometry, capturing the temporal evolution of the photon escape fraction that is out of phase with the star formation rate, fully consistent with hydrodynamic simulations. We advocate for integral field unit spectroscopy to better constrain flow properties.

astro-ph.GA↗
arXiv2025

The Cosmic Evolution Early Release Science Survey (CEERS)

We present the Cosmic Evolution Early Release Science (CEERS) Survey, a 77.2 hour Director's Discretionary Early Release Science Program. CEERS demonstrates, tests, and validates efficient extragalactic surveys using coordinated, overlapping parallel observations with the JWST instrument suite, including NIRCam and MIRI imaging, NIRSpec low (R~100) and medium (R~1000) resolution spectroscopy, and NIRCam slitless grism (R~1500) spectroscopy. CEERS targets the Hubble Space Telescope-observed region of the Extended Groth Strip (EGS) field, supported by a rich set of multiwavelength data. CEERS facilitated immediate community science in both of the extragalactic core JWST science drivers ``First Light" and ``Galaxy Assembly," including: 1) The discovery and characterization of large samples of galaxies at z >~ 10 from ~90 arcmin^2 of NIRCam imaging, constraining their abundance and physical nature; 2) Deep spectra of >1000 galaxies, including dozens of galaxies at 6 3; and 4) Characterizing galaxy mid-IR emission with MIRI to study dust-obscured star-formation and supermassive black hole growth at z~1-3. As a legacy product for the community, the CEERS team has provided several data releases, accompanied by detailed notes on the data reduction procedures and notebooks to aid in reproducibility. In addition to an overview of the survey and quality of the data, we provide science highlights from the first two years with CEERS data.

astro-ph.GA↗
arXiv2024

Preliminary Evidence for Lensing-Induced Alignments of High-Redshift Galaxies in JWST-CEERS

The majority of low-mass ($\log_{10} M_*/M_{\odot}=9-10$) galaxies at high redshift ($z>1$) appear elongated in projection. We use JWST-CEERS observations to explore the role of gravitational lensing in this puzzle. The typical galaxy-galaxy lensing shear $\gamma\sim1\%$ is too low to explain the predominance of elongated early galaxies with ellipticity $e\approx0.6$. However, non-parametric quantile regression with Bayesian Additive Regression Trees reveals hints of an excess of tangentially-aligned source-lens pairs with $\gamma>10\%$. On larger scales, we also find evidence for weak lensing shear. We rule out the null hypothesis of randomly oriented galaxies at $\gtrsim99\%$ significance in multiple NIRCam chips, modules and pointings. The number of such regions is small and attributable to chance, but coherent alignment patterns suggest otherwise. On the chip scale, the average complex ellipticity $\langle e\rangle\sim10\%$ is non-negligible and beyond the level of our PSF uncertainties. The shear variance $\langle\overline{\gamma}^2\rangle\sim10^{-3}$ is an order of magnitude above the conventional weak lensing regime but is more sensitive to PSF systematics, intrinsic alignments, cosmic variance and other biases. Taking it as an upper limit, the maximum implied ``cosmic shear'' is only a few percent and cannot explain the elongated shapes of early galaxies. The alignments themselves may arise from lensing by a protocluster or filament at $z\sim0.75$ where we find an overabundance of massive lens galaxies. We recommend a weak lensing search for overdensities in ``blank'' deep fields with JWST and the Roman Space Telescope.

astro-ph.GA↗
arXiv2024

LtU-ILI: An All-in-One Framework for Implicit Inference in Astrophysics and Cosmology

This paper presents the Learning the Universe Implicit Likelihood Inference (LtU-ILI) pipeline, a codebase for rapid, user-friendly, and cutting-edge machine learning (ML) inference in astrophysics and cosmology. The pipeline includes software for implementing various neural architectures, training schemata, priors, and density estimators in a manner easily adaptable to any research workflow. It includes comprehensive validation metrics to assess posterior estimate coverage, enhancing the reliability of inferred results. Additionally, the pipeline is easily parallelizable and is designed for efficient exploration of modeling hyperparameters. To demonstrate its capabilities, we present real applications across a range of astrophysics and cosmology problems, such as: estimating galaxy cluster masses from X-ray photometry; inferring cosmology from matter power spectra and halo point clouds; characterizing progenitors in gravitational wave signals; capturing physical dust parameters from galaxy colors and luminosities; and establishing properties of semi-analytic models of galaxy formation. We also include exhaustive benchmarking and comparisons of all implemented methods as well as discussions about the challenges and pitfalls of ML inference in astronomical sciences. All code and examples are made publicly available at https://github.com/maho3/ltu-ili.

astro-ph.IM↗
arXiv2024

Galaxies Going Bananas: Inferring the 3D Geometry of High-Redshift Galaxies with JWST-CEERS

The 3D geometry of high-redshift galaxies remains poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in JWST-CEERS observations with $\log M_*/M_{\odot}=9.0-10.5$ at $z=0.5-8.0$. We reproduce previous results from HST-CANDELS in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size and covariances with samples as small as $\sim50$ galaxies. We find high 3D ellipticities for all mass-redshift bins suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be $\sim1$ for $\log M_*/M_{\odot}=9.0-9.5$ dwarfs at $z>1$ (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a ``banana'' in the projected $b/a-\log a$ diagram with an excess of low $b/a$, large $\log a$ galaxies. The dwarf prolate fraction rises from $\sim25\%$ at $z=0.5-1.0$ to $\sim50-80\%$ at $z=3-8$. If these are disks, they cannot be axisymmetric but instead must be unusually oval (triaxial) unlike local circular disks. We simultaneously constrain the 3D size-mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar Sérsic indices ($n\sim1$), non-parametric morphological properties and specific star formation rates. Both tend to be visually classified as disks or irregular but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects and theoretical implications.

astro-ph.GA↗
arXiv2023

CEERS Key Paper I: An Early Look into the First 500 Myr of Galaxy Formation with JWST

We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z~0.5 to z>10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 sq. arcmin, to search for candidate galaxies at z>9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multi-band photometry across seven NIRCam broad and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z~9-16. These objects are compact with a median half-light radius of ~0.5 kpc. We present an early estimate of the z~11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M_UV ~ -20 appears to evolve very little from z~9 to z~11. We also find that the abundance (surface density [arcmin^-2]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z>10 star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star-formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultra-high-redshift galaxies with which to further explore these conclusions.

astro-ph.GA↗
arXiv2023

Evolution of the Size-Mass Relation of Star-forming Galaxies Since $z=5.5$ Revealed by CEERS

We combine deep imaging data from the CEERS early release JWST survey and HST imaging from CANDELS to examine the size-mass relation of star-forming galaxies and the morphology-quenching relation at stellar masses $\textrm{M}_{\star} \geq 10^{9.5} \ \textrm{M}_{\odot}$ over the redshift range $0.5 < z < 5.5$. In this study with a sample of 2,450 galaxies, we separate star-forming and quiescent galaxies based on their star-formation activity and confirm that star-forming and quiescent galaxies have different morphologies out to $z=5.5$, extending the results of earlier studies out to higher redshifts. We find that star-forming and quiescent galaxies have typical Sérsic indices of $n\sim1.3$ and $n\sim4.3$, respectively. Focusing on star-forming galaxies, we find that the slope of the size-mass relation is nearly constant with redshift, as was found previously, but shows a modest increase at $z \sim 4.2$. The intercept in the size-mass relation declines out to $z=5.5$ at rates that are similar to what earlier studies found. The intrinsic scatter in the size-mass relation is relatively constant out to $z=5.5$.

astro-ph.GA↗
arXiv2023

A unified model for the co-evolution of galaxies and their circumgalactic medium: the relative roles of turbulence and atomic cooling physics

The circumgalactic medium (CGM) plays a pivotal role in regulating gas flows around galaxies and thus shapes their evolution. However, the details of how galaxies and their CGM co-evolve remain poorly understood. We present a new time-dependent two-zone model that self-consistently tracks not just mass and metal flows between galaxies and their CGM but also the evolution of the global thermal and turbulent kinetic energy of the CGM. Our model accounts for heating and turbulence driven by both supernova winds and cosmic accretion as well as radiative cooling, turbulence dissipation, and halo outflows due to CGM overpressurization. We demonstrate that, depending on parameters, the CGM can undergo a phase transition (``thermalization'') from a cool, turbulence-supported phase to a virial-temperature, thermally-supported phase. This CGM phase transition is largely determined by the ability of radiative cooling to balance heating from supernova winds and turbulence dissipation. We perform an initial calibration of our model to the FIRE-2 cosmological hydrodynamical simulations and show that it can approximately reproduce the baryon cycles of the simulated halos. In particular, we find that, for these parameters, the phase transition occurs at high-redshift in ultrafaint progenitors and at low redshift in classical $M_{\rm vir}\sim10^{11}M_{\odot}$ dwarfs, while Milky Way-mass halos undergo the transition at $z\approx0.5$. We see a similar transition in the simulations though it is more gradual, likely reflecting radial dependence and multi-phase gas not captured by our model. We discuss these and other limitations of the model and possible future extensions.

astro-ph.GA↗
arXiv2023

Over 500 Days in the Life of the Photosphere of the Type Iax Supernova SN 2014dt

Type Iax supernovae (SN Iax) are the largest known class of peculiar white dwarf supernovae, distinct from normal Type Ia supernovae (SN Ia). The unique properties of SN Iax, especially their strong photospheric lines out to extremely late times, allow us to model their optical spectra and derive physical parameters for the long-lasting photosphere. We present an extensive spectral timeseries, including 21 new spectra, of SN Iax 2014dt from +11 to +562 days after maximum light. We are able to reproduce the entire timeseries with a self-consistent, nearly unaltered deflagration explosion model from Fink et al. (2014) using TARDIS, an open-source radiative transfer code (Kerzendorf & Sim 2014; Kerzendorf et al. 2023). We find that the photospheric velocity of SN 2014dt slows its evolution between +64 and +148 days, which closely overlaps the phase when we see SN 2014dt diverge from the normal spectral evolution of SN Ia (+90 to +150 days). The photospheric velocity at these epochs, ~400$-$1000 km s$^{-1}$, may demarcate a boundary within the ejecta below which the physics of SN Iax and normal SN Ia differ. Our results suggest that SN 2014dt is consistent with a weak deflagration explosion model that leaves behind a bound remnant and drives an optically thick, quasi-steady-state wind creating the photospheric lines at late times. The data also suggest that this wind may weaken at epochs past +450 days, perhaps indicating a radioactive power source that has decayed away.

astro-ph.HE↗
arXiv2023

Public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation

We describe a public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation, available at http://flathub.flatironinstitute.org/fire, from the Feedback In Realistic Environments (FIRE) project. FIRE-2 simulations achieve parsec-scale resolution to explicitly model the multi-phase interstellar medium while implementing direct models for stellar evolution and feedback, including stellar winds, core-collapse and Ia supernovae, radiation pressure, photoionization, and photoelectric heating. We release complete snapshots from 3 suites of simulations. The first comprises 20 simulations that zoom in on 14 Milky Way-mass galaxies, 5 SMC/LMC-mass galaxies, and 4 lower-mass galaxies including 1 ultra-faint; we release 39 snapshots across z = 0 - 10. The second comprises 4 massive galaxies, with 19 snapshots across z = 1 - 10. Finally, a high-redshift suite comprises 22 simulations, with 11 snapshots across z = 5 - 10. Each simulation also includes dozens of resolved lower-mass (satellite) galaxies in its zoom-in region. Snapshots include all stored properties for all dark matter, gas, and star particles, including 11 elemental abundances for stars and gas, and formation times (ages) of star particles. We also release accompanying (sub)halo catalogs, which include galaxy properties and member star particles. For the simulations to z = 0, including all Milky Way-mass galaxies, we release the formation coordinates and an "ex-situ" flag for all star particles, pointers to track particles across snapshots, catalogs of stellar streams, and multipole basis expansions for the halo mass distributions. We describe publicly available python packages for reading and analyzing these simulations.

astro-ph.GA↗
arXiv2023

CEERS Key Paper III: The Diversity of Galaxy Structure and Morphology at z=3-9 with JWST

We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z=3-9 using early JWST CEERS NIRCam observations. Our sample consists of 850 galaxies at z>3 detected in both CANDELS HST imaging and JWST CEERS NIRCam images to enable a comparison of HST and JWST morphologies. Our team conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. We also measure quantitative morphologies using the publicly available codes across all seven NIRCam filters. Using these measurements, we present the fraction of galaxies of each morphological type as a function of redshift. Overall, we find that galaxies at z>3 have a wide diversity of morphologies. Galaxies with disks make up a total of 60\% of galaxies at z=3 and this fraction drops to ~30% at z=6-9, while galaxies with spheroids make up ~30-40% across the whole redshift range and pure spheroids with no evidence for disks or irregular features make up ~20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (~40-50%), while those that are purely irregular increases from ~12% to ~20% at z>4.5. We note that these are apparent fractions as many selection effects impact the visibility of morphological features at high redshift. The distributions of Sérsic index, size, and axis ratios show significant differences between the morphological groups. Spheroid Only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than Disk/Irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study and further work with large samples at higher redshift is needed to quantify when these features first formed.

astro-ph.GA↗