arXiv subjects

Andrea Gebek

Publications and source records attributed to Andrea Gebek.

At least 19 recordsLinked to original sources

arXiv2026

The TNG50-SKIRT Atlas: Spatially resolved synthetic galaxies from the ultraviolet to the submillimetre (DR2)

We present the second data release (DR2) of the TNG50-SKIRT Atlas (TSA), a library of synthetic, spatially resolved galaxy observables. The atlas is constructed by post-processing a stellar-mass-complete ($10^{9.8}~{\text{M}}_\odot < M_\star < 10^{12}~{\text{M}}_\odot$) sample of 1154 $z=0$ galaxies from the TNG50 cosmological hydrodynamical simulation with the Monte Carlo radiative transfer code SKIRT. Compared to the first release, TSA DR2 extends the wavelength coverage from the ultraviolet to the submillimetre, including dust emission, and incorporates updated stellar population models together with an improved treatment of dust-enshrouded star-forming regions. The atlas provides spatially resolved spectral energy distributions, broadband images, and physical property maps for multiple viewing orientations, as well as a catalogue of integrated properties enabling direct comparison with unresolved observations. We validate the data products through extensive quality control, including an assessment of Monte Carlo noise, and demonstrate their internal consistency using diagnostic relations between luminosities and star formation rates. TSA DR2 provides a versatile resource for studies of dust attenuation and emission, star formation tracers, galaxy morphology, and multi-wavelength scaling relations across spatial scales. The atlas and associated data products are publicly released and are intended to support a wide range of observationally oriented studies of galaxy evolution.

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arXiv2026

The evolution of galaxy dust scaling relations in the COLIBRE simulations

We present dust scaling relations across cosmic time ($0 \le z \le 15$) for galaxies in the COLIBRE cosmological simulations. COLIBRE self-consistently tracks dust production, growth, destruction, and grain size evolution within a multiphase interstellar medium. Using volumes up to $(400\, {\rm cMpc})^3$ at three mass resolutions ($10^{5}-10^7$ M$_{\odot}$), we predict the dust mass function, cosmic dust mass density, and key dust scaling relations (dust-to-gas ratio, dust-to-metal ratio, grain species fractions, and grain sizes) as functions of galaxy metallicity, stellar mass, and dust mass. The model broadly reproduces most observed relations across cosmic time, matching closest at the highest resolution. We find that silicates dominate the dust mass ($\gtrsim 70\%$) at all epochs, and while large grains dominate in the early Universe ($z \ge 5$), their mass fraction declines to become comparable to small grains by $z=0$. At $z < 1$, the simulated dust mass functions align well with observations, but the cosmic dust mass density is systematically high by $\lesssim 0.3$ dex, while in agreement with observations at higher redshifts. Additionally, the simulations underpredict the extreme dust masses of bright sub-millimeter galaxies at $z \ge 2$. We demonstrate that scaling relations are sensitive to numerical resolution only in the low-redshift, low-mass regime; while their normalisation is influenced by gas-phase selection. These findings highlight both the predictive power and resolution-dependent limits of cosmological dust models, providing essential insights to refine ISM physics.

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arXiv2026

Cosmological simulations of the high-redshift galaxy population adopting a variable stellar initial mass function

JWST surveys reveal a greater space density of high-redshift UV-bright galaxies than predicted by conventional galaxy formation models. We present results from a $L=100$ cMpc cosmological simulation evolved to $z=5$ with a variation of the COLIBRE galaxy formation model that adopts a density-dependent stellar initial mass function (IMF), such that stellar populations formed from dense gas are born with a top-heavy IMF. Crucially, heavy element and dust yields, and supernova feedback energetics, are self-consistently adjusted to the changing IMF. We model UV/optical emission (including nebular emission) from galaxies and its attenuation by dust. By allowing a significant fraction of high-redshift star formation to proceed with a top-heavy IMF, the rest-frame far-UV luminosities of early galaxies are elevated by up to a factor of $\simeq4$ with respect to the fiducial COLIBRE L100m6 simulation, which assumes a universal Chabrier IMF. This enables the formation of galaxies with observed brightness up to $M_{\rm UV} \simeq -20$ at $z=15$ (c.f. $M_{\rm UV} \simeq -18.5$ in the fiducial simulation), illustrating the potential of star formation with a top-heavy IMF to alleviate tensions with JWST data. Later, the boost in far-UV emission is partly offset by attenuation due to increased dust surface densities from i) additional dust grain ejection from core-collapse supernovae and ii) efficient grain growth promoted by more metal-rich interstellar gas. The simulation reproduces the $z=5$ galaxy stellar mass function and rest-frame optical luminosity function with comparable accuracy to the fiducial simulation, and both simulations exhibit UV continuum slopes that are consistent with JWST observations.

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arXiv2026

The COLIBRE-SKIRT pipeline: Calibration-free dust radiative transfer postprocessing for cosmological simulations

Context. Three-dimensional dust radiative transfer provides a powerful framework to connect cosmological galaxy simulations to multiwavelength observations. Until recently, in large-volume simulations, the formation of a cold ISM phase was prevented and dust was not evolved self-consistently. This required calibration of dust-to-metal ratios and extra subgrid dust attenuation in birth clouds, thereby reducing the predictive power. Aims. We present the COLIBRE-SKIRT pipeline, a calibration-free dust radiative transfer framework for the novel COLIBRE suite of large-volume cosmological simulations, which include a live dust model and directly simulate the multiphase ISM. Our primary aim is to establish a reference pipeline for generating multiwavelength mock observables from these simulations. As a first application, we produce far-ultraviolet (FUV) to far-infrared (FIR) spatially integrated spectra and assess them by comparison with the observed low-redshift cosmic spectral energy distribution (CSED). Methods. We apply the SKIRT dust radiative transfer code to the COLIBRE simulations. Dust masses and species fractions are taken directly from the simulation, and no birth cloud model is added in postprocessing. We introduce a "split & scale" approach that maps the simulated two-size, multi-species dust distribution onto continuous grain size distributions without introducing free parameters. Results. We find that, for the first time, a large-volume cosmological simulation directly reproduces the local Universe CSED without calibrating the postprocessing routine a priori. Residual tensions in the mid-infrared (~0.2 dex) point towards insufficient heating of the hottest dust components and uncertainties in the modelling of the PAH-emission carriers. This framework can be readily applied at low and high redshift to create synthetic spectra and images from the FUV to the FIR.

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arXiv2026

Predicting ionised gas emission in 3D with SKIRT. I. Framework and validation

Emission lines from ionised gas are key diagnostics of star formation, metallicity, and ionisation conditions in galaxies. Interpreting spatially resolved observations from integral-field surveys (e.g. MaNGA, MUSE, JWST/NIRSpec) and comparing them with hydrodynamical simulations requires 3D photoionisation models that handle realistic geometries, dust attenuation, and synthetic instrument output. We present a new photoionisation module for the Monte Carlo radiative transfer code SKIRT that predicts emission-line luminosities of ionised gas in 3D, combining pre-computed Cloudy tables for gas temperature and opacity with a direct calculation of ion fractions and line emissivities. The local ionising radiation field (1-6 Ryd) is characterised by log U and four spectral-shape ratios; Cloudy tables map these to temperature and opacity, converging through SKIRT's existing iteration cycle. An inline solver then determines ion fractions from the converged field and temperature and evaluates line emissivities. We validate against Cloudy on 60 spherical shell models and against COLT on a Milky Way-analogue galaxy. On the 1D grid, hydrogen recombination lines agree with Cloudy to within a few per cent (Halpha median ratio 0.97) and the forbidden lines to within ~5%, except [S II] 6717 (1.23), whose offset traces a temperature overestimate near the ionisation front. In 3D, integrated luminosities agree with COLT to within 18% for the hydrogen lines and 2% for [N II], while [O III] and [S II] are elevated by ~70 and ~80%. Pixel-by-pixel correlation coefficients reach r >= 0.92, with luminosity-weighted scatter of 0.14-0.31 dex and broadly consistent BPT ratios. The module enables self-consistent synthetic observations in which ionised-gas emission lines, dust attenuation, and dust re-emission are computed in a single MCRT run, applicable to any hydrodynamical simulation.

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arXiv2026

TODDLERS 2.0: Stellar feedback and observables across diverse IMFs, binary populations, and cloud environments

Modeling the feedback-driven evolution of star-forming regions and their multi-wavelength emission is essential for interpreting galaxy observations across cosmic time. TODDLERS couples 1D shell dynamics with Cloudy photoionization to predict UV-to-mm observables. The original framework assumed instantaneous star formation, uniform cloud density, a fixed IMF with single-star evolution, and fixed dust properties. We present TODDLERS 2.0, extending the framework to broader stellar populations, birth-cloud conditions, and dust physics. Stellar feedback and input spectra are modeled using pySTARBURST99 (arbitrary IMFs, upper mass limits up to 500 M$\odot$) and BPASS (binary evolution, upper mass limits up to 300 M$\odot$), including stochastic IMF sampling for low-mass clusters (M$* \lesssim 10^4$ M$\odot$) and constant star formation. The 1D evolution includes non-uniform cloud density profiles and dynamic cloud density evolution driven by escaping ionizing radiation. Cloudy post-processing includes modified grain size distributions and diffuse ionized gas. Cloud density profile and star formation mode regulate fragmentation timescales and shell extent: centrally concentrated profiles fragment earlier, while constant star formation delays fragmentation relative to bursts. Top-heavy IMFs generate stronger feedback and earlier fragmentation than a Kroupa IMF. Dynamic cloud density evolution introduces an additional feedback channel, strongest at low metallicity where unswept cloud density decreases by up to three orders of magnitude. For low-mass clusters, stochastic sampling produces order-of-magnitude feedback variations, demonstrating breakdown of the fully sampled IMF approximation. TODDLERS 2.0 models diverse stellar populations, cloud structures, and star formation modes as a standalone tool or sub-grid emission model for galaxy simulations.

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arXiv2026

The TNG50-SKIRT Atlas: Multi-wavelength nonparametric galaxy morphology

Context: Galaxy morphology is a fundamental property to describe galaxy evolution. However, the observed morphology of a particular galaxy may depend on the observed wavelength. Aims: Our aim is to investigate the wavelength dependence and the effect of dust attenuation on nonparametric morphology indicators. Methods: We use the TNG50-SKIRT Atlas, an atlas of synthetic UV to near-infrared (NIR) broadband images for a complete stellar-mass-selected sample of 1154 galaxies extracted from the TNG50 cosmological simulation at $z = 0$. For each image, we calculate four nonparametric morphology indicators using the StatMorph code. Results: We find that the known correlations between the stellar mass and the morphological parameters measured in the optical, together with the Gini-$M_{20}$, concentration-Gini, and concentration-$M_{20}$ planes, are fully consistent with observational data. However, nonparametric morphological indicators change significantly with wavelength and that this wavelength dependence is stronger for disc-dominated than for bulge-dominated galaxies. The wavelength dependence of the morphology of our simulated TNG50 galaxies is consistent with measurements of local galaxies from the SINGS survey. We demonstrate that the effect of dust attenuation on nonparametric morphology indicators is modest across the full galaxy population but can be significant for individual galaxies.

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arXiv2026

The galaxy ultraviolet luminosity function from $z=7$ to $15$ in the COLIBRE simulations

JWST has enabled the detection of galaxies in the earliest stages of cosmic history. We compare the ultraviolet luminosity functions (UVLFs) at redshifts $z=7-15$ predicted by the new cosmological hydrodynamics simulations, COLIBRE with observations, including those from JWST. The UV luminosities of COLIBRE galaxies are derived using the radiative transfer code SKIRT, which tracks stellar emission and its processing through the multi-phase interstellar medium and dust distribution predicted by COLIBRE. We find that although COLIBRE is consistent with the observed evolution of the stellar mass function up to $z=12$, its dust-attenuated UVLFs fall systematically below the observations at the bright end: at the number density of $10^{-6}\,\mathrm{Mpc^{-3}\,mag^{-1}}$, the brightest galaxies are underluminous by $\approx 1\,\rm mag$ at $z=7$, increasing to $\approx 2.5\,\rm mag$ at $z=15$. Accounting for observational uncertainties brings the COLIBRE UVLFs closer to the observational data, but does not fully resolve the discrepancy. Ignoring dust attenuation allows COLIBRE to produce sufficiently bright galaxies at $7\lesssim z \lesssim 12$, while at $z=15$, COLIBRE still underpredicts the luminosities of the brightest galaxies, indicating the need for additional physical mechanisms to boost the UV luminosities at the earliest cosmic epochs, such as a ''top-heavy'' stellar initial mass function. We fit the COLIBRE UVLFs with Schechter functions and calculate the evolution of the best-fit parameters. We find that the galaxy number density decreases, the characteristic luminosity becomes fainter and the faint-end slope becomes steeper towards higher redshifts. The UV luminosity density decreases by a factor of $\approx 300$ from $z = 7$ to $z = 15$.

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arXiv2026

Galaxy luminosity functions from far-UV to submillimetre at $z=0$ in the COLIBRE simulations

We present predictions from the recent COLIBRE cosmological hydrodynamical simulations of galaxy formation for the present-day galaxy luminosity functions (LFs) at wavelengths ranging from the far-ultraviolet (FUV) to the submillimetre. The simulations are post-processed with the radiative transfer code SKIRT, accounting for dust attenuation and emission using the distribution and properties of dust grains predicted directly by COLIBRE. Results from simulations varying in mass resolution by a factor of $\sim 10^2$ ($\sim 10^5 - 10^7\,\mathrm{M_{\odot}}$) show very good convergence over most luminosity ranges. The COLIBRE-SKIRT LFs match the data remarkably well from the FUV to the near-infrared ($3.4\,\mathrm{\mu m}$) and also in the far-infrared and submillimetre wavelength range ($70-850\,\mathrm{\mu m}$). In the mid-infrared (MIR; $8-24\,\mathrm{\mu m}$), COLIBRE-SKIRT matches the data well at low luminosities but significantly underpredicts the luminosities of MIR-bright galaxies, with the discrepancy increasing towards longer wavelengths. The total infrared LF, obtained by integrating the spectral energy distributions over $8-1000\,\mathrm{\mu m}$, also matches observations well at the faint end but underpredicts the number of very bright galaxies. The unprecedented agreement at all other wavelengths indicates that COLIBRE, coupled with this calibration-free SKIRT post-processing framework, successfully predicts the properties of stellar populations at the present day and the amount and distribution of interstellar dust.

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arXiv2025

Generating LSB-optimised synthetic images for simulated galaxies

We introduce an emission-biasing scheme in the SKIRT radiative transfer code that enables efficient generation of synthetic galaxy images optimized for low-surface-brightness (LSB) science. Standard Monte Carlo radiative transfer simulations achieve high signal-to-noise in bright regions but require prohibitively many photon packets to reach reliable depth in galaxy outskirts. By assigning stellar particles bias factors that scale with their smoothing lengths, our method boosts photon emission from low-density regions while conserving energy through weight corrections. Tests on a Milky-Way-like galaxy from the TNG50 cosmological simulation show that bias factors proportional to the smoothing length substantially extend the reliable LSB regime, providing an inexpensive improvement for deep synthetic imaging of simulated galaxies.

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arXiv2025

Evolution and Mass Dependence of UV-to-near-IR Color Gradients up to z=2.5 from HST+JWST

We present the redshift evolution of radial color gradients (in rest-frame ${\textit{U}} - {\textit{V}}$ and ${\textit{V}} - {\textit{J}}$) for galaxies in the range $0.5<$ z $<2.5$ and investigate their origin and dependence on stellar mass. We select $\sim 10,200$ galaxies with stellar masses $M_\star>10^{9.5}~{\text{M}}_\odot$ from publicly available JWST/NIRCam-selected catalogs. Using 2D S\'ersic profile fits to account for PSF broadening, we perform spatially resolved SED fitting on HST and JWST/NIRCam photometry retrieving accurate rest-frame ${\textit{U}} - {\textit{V}}$ and ${\textit{V}} - {\textit{J}}$ color gradients within 2$R_\text{e, F444W}$. Star-forming galaxies generally exhibit negative ${\textit{V}} - {\textit{J}}$ color gradients that are strongly mass and redshift dependent. For massive star-forming galaxies ($M_\star>10^{10.5}~{\text{M}}_\odot$) at $z>1.5$ ${\textit{V}} - {\textit{J}}$ colors are $\approx 0.5$ mag redder within the effective radius than outside, on average. We find that, at all redshifts and across the entire stellar mass range, ${\textit{V}} - {\textit{J}}$ gradients strongly correlate with global attenuation ($A_V$), suggesting that they predominantly trace dust attenuation gradients. Edge-on galaxies are redder and have stronger gradients at all $z$, although the correlation weakens at higher $z$. The ${\textit{U}} - {\textit{V}}$ and ${\textit{V}} - {\textit{J}}$ color gradients in the quiescent galaxy population, in contrast, are weakly negative (from $\approx -0.1$ to $\approx- 0.2$ mag), though significant, and show little or no dependence on stellar mass, redshift or axis ratio. The implication is that quiescent galaxies must be largely transparent, with low $A_V$, and color gradients mostly attributable to stellar population gradients.

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arXiv2025

Volcanic Satellites Tidally Venting Na, K, SO2 in Optical & Infrared Light

Recent infrared spectroscopy from the James Webb Space Telescope (JWST) has spurred analyses of common volcanic gases such as carbon dioxide (CO2), sulfur dioxide (SO2), alongside alkali metals sodium (Na I) and potassium (K I) surrounding the hot Saturn WASP-39 b. We report more than an order-of-magnitude of variability in the density of neutral Na, K, and SO2 between ground-based measurements and JWST, at distinct epochs, hinting at exogenic physical processes similar to those sourcing Io's extended atmosphere and torus. Tidally-heated volcanic satellite simulations sputtering gas into a cloud or toroid orbiting the planet, are able to reproduce the probed line-of-sight column density variations. The estimated SO2 flux is consistent with tidal gravitation predictions, with a Na/SO2 ratio far smaller than Io's. Although stable satellite orbits at this system are known to be < 15.3 hours, several high-resolution alkali Doppler shift observations are required to constrain a putative orbit. Due to the Roche limit interior to the planetary photosphere at ~ 8 hours, atmosphere-exosphere interactions are expected to be especially important at this system.

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arXiv2025

Evolution of galaxy attenuation curves driven by evolving dust mass and grain size distributions

We investigate the impacts of the evolution of dust mass and grain size distribution within a Milky Way-like (MW-like) galaxy simulation on global attenuation curves, focusing on the optical-UV slope and the 2175 $AA$ bump. We discuss the contributions of star-dust geometry, scattering, and dust properties. Post-processing dust radiative transfer was performed using SKIRT based on the MW-like galaxy simulation. The simulation was carried out with GADGET4-OSAKA, which models the evolution of grain size distributions. For lower inclination angles (closer to face-on), the attenuation curve flattens over time up to t=1 Gyr, then becomes progressively steeper. This steeper slope arises from the interplay between scattering and the dust disk becoming more extended over time (changes in star-dust geometry). At higher inclination, scattering is suppressed, and the attenuation curves slightly steepen over time due to small-grain formation and the bias of observed UV light toward older stars. The bump strengthens on a timescale of ~250 Myr due to the formation of small carbonaceous grains. The bump strength is affected not only by the abundance of small grains but also by star-dust geometry. At higher $A_V$ or higher inclination, the bump weakens. These results may help interpret flatter attenuation curves and weaker bumps in high-redshift galaxies. Variations in star-dust geometry alter the amount of scattered photons escaping the galaxy, driving the anti-correlation between the slope and $A_V$. Scatter in this relation arises from differences in dust optical depth along and perpendicular to the line of sight, reflecting inclination and star-dust geometry. Additional contributions come from variations in grain size distribution and the fraction of obscured young stars.

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arXiv2025

The COLIBRE project: cosmological hydrodynamical simulations of galaxy formation and evolution

We present the COLIBRE galaxy formation model and the COLIBRE suite of cosmological hydrodynamical simulations. COLIBRE includes new models for radiative cooling, dust grains, star formation, stellar mass loss, turbulent diffusion, pre-supernova stellar feedback, supernova feedback, supermassive black holes and active galactic nucleus (AGN) feedback. The multiphase interstellar medium is explicitly modelled without a pressure floor. Hydrogen and helium are tracked in non-equilibrium, with their contributions to the free electron density included in metal-line cooling calculations. The chemical network is coupled to a dust model that tracks three grain species and two grain sizes. In addition to the fiducial thermally-driven AGN feedback, a subset of simulations uses black hole spin-dependent hybrid jet/thermal AGN feedback. To suppress spurious transfer of energy from dark matter to stars, dark matter is supersampled by a factor 4, yielding similar dark matter and baryonic particle masses. The subgrid feedback model is calibrated to match the observed $z \approx 0$ galaxy stellar mass function, galaxy sizes, and black hole masses in massive galaxies. The COLIBRE suite includes three resolutions, with particle masses of $\sim 10^5$, $10^6$, and $10^7\,\text{M}_\odot$ in cubic volumes of up to 100, 200, and 400 cMpc on a side, respectively. The largest runs use 136 billion ($5 \times 3008^3$) particles. We describe the model, assess its strengths and limitations, and present both visual impressions and quantitative results. Comparisons with various low-redshift galaxy observations generally show very good numerical convergence and excellent agreement with the data.

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arXiv2025

Doppler Shifted Transient Sodium Detection by KECK/HIRES

We carried out the first high-resolution transit observations of the exoplanet WASP-49 Ab with Keck/HIRES. Upon custom wavelength calibration we achieve a Doppler RV precision of $<$ 60 ${\rm m\,s}^{-1}$. This is an improvement in RV stability of roughly 240 ${\rm m\,s}^{-1}$ with respect to the instrument standard. We report an average sodium flux residual of $\Delta \mathcal{F}_{NaD}/ \mathcal{F}_{\star} (\lambda) \sim$ 3.2 $\pm$ 0.4 $\%$ (8.0 $\sigma$) comparable to previous studies. Interestingly, an average Doppler shift of -6.2 $\pm$ 0.5 ${\rm km\,s}^{-1}$ (12.4 $\sigma$) is identified offset from the exoplanet rest frame. The velocity residuals \textit{in time} trace a blueshift (v$_{\Gamma, ingress} \sim$ -10.3 $\pm$ 1.9 ${\rm km\,s}^{-1}$) to redshift (v$_{\Gamma, egress} \sim$ +4.1 $\pm$ 1.5 ${\rm km\,s}^{-1}$) suggesting the origin of the observed sodium is unlikely from the atmosphere of the planet. The average Na light curves indicate a depth of $\Delta \mathcal{F}_{NaD} /\mathcal{F}_{\star} (t) \sim$ 0.47 $\pm$ 0.04 % (11.7 $\sigma$) enduring $\lesssim$ 90 minutes with a half-max duration of $\sim$ 40.1 minutes. Frequent high-resolution spectroscopic observations will be able to characterize the periodicity of the observed Doppler shifts. Considering the origin of the transient sodium gas is of unknown geometry, a co-orbiting natural satellite may be a likely source.

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arXiv2025

The multi-wavelength Tully-Fisher relation in the TNG50 cosmological simulation

The Tully-Fisher relation (TFR) is one of the most important and widely used empirical correlations in extragalactic astronomy. Apart from its importance as a secondary distance indicator, the TFR relation serves as a test for galaxy evolution models, because it connects the baryonic and dark matter components of galaxies. We aim at simulating the multi-wavelength TFR relation from UV to mid-infrared wavelengths for the TNG50 cosmological simulation at $z = 0$, and at comparing the results with observational TFR studies. We want to compare the wavelength dependence of the slope and scatter with the observed values, and search for secondary parameters that reduce the scatter in the TFR. We select a large sample of simulated late-type, disc-dominated galaxies from the TNG50 simulation. For each galaxy, we use the SKIRT radiative transfer code to generate realistic synthetic global fluxes in 12 UV to mid-infrared broadbands and synthetic integrated HI line profiles. We use bivariate linear regression to determine the TFR in each band, and we search for a second TFR parameter by correlating the residuals with different physical parameters. Our TNG50 TFR reproduces the characteristic behaviour of the observed TFR in many studies: the TFR becomes steeper and tighter as we move from UV/optical to infrared wavelengths. The slope changes from $-7.46 \pm 0.14~{\text{mag}}~{\text{dex}}^{-1}$ in the NUV band to $-9.66 \pm 0.09~{\text{mag}}~{\text{dex}}^{-1}$ in the IRAC [4.5] band. Quantitatively, our slopes are well within the spread of different observational results. The ${\textit{u}} - {\textit{r}}$ colour or the sSFR can significantly reduce the scatter in the UV and optical bands. Using ${\textit{u}} - {\textit{r}}$ colour as second parameter, the modified TFR has a roughly constant intrinsic tightness of over the entire UV to MIR range. The combination of the TNG50...

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arXiv2025

The mass-dependent UVJ diagram at cosmic noon: A challenge for galaxy evolution models and dust radiative transfer

Context. The UVJ color-color diagram is a widely used diagnostic to separate star-forming and quiescent galaxies. Observational data from photometric surveys reveal a strong stellar mass trend, with higher-mass star-forming galaxies being systematically more dust-reddened. Aims. We analyze the UVJ diagram in the TNG100 cosmological simulation at cosmic noon ($z\approx2$). Specifically, we focus on the trend between UVJ colors and mass which has not been reproduced in any cosmological simulation thus far. Methods. We applied the SKIRT dust radiative transfer code to the TNG100 simulation to generate rest-frame UVJ fluxes. These UVJ colors were then compared to observational data from several well-studied extragalactic fields from the CANDELS/3D-HST programs, augmented by recent JWST/NIRCam photometry. Results. Quiescent and low-mass ($M_\star\lesssim10^{10.5}\,\mathrm{M}_\odot$) galaxies at cosmic noon do not require significant levels of dust reddening, as opposed to massive ($M_\star\gtrsim10^{11}\,\mathrm{M}_\odot$) star-forming galaxies. An extensive range of possible dust models fall short of the required dust reddening in V-J color for massive star-forming galaxies, with the simulated galaxies being too blue by $\approx0.9\,\mathrm{mag}$. Conclusions. We find that only variations in the star-to-dust geometries of the simulated galaxies can yield V-J colors that are red enough to match the observations. A toy model with isolated dust screens around younger stellar populations (with ages below $\sim1\,\mathrm{Gyr}$) can reproduce the observational data, while all conventional dust radiative transfer models (where the dust distribution follows the metals in the interstellar medium) fail to achieve the required V-J colors.

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arXiv2025

Evolution of the S\'ersic Index up to z=2.5 from JWST and HST

The James Webb Space Telescope (JWST) is unveiling the rest-frame near-IR structure of galaxies. We measure the evolution with redshift of the rest-frame optical and near-IR S\'ersic index ($n$), and examine the dependence on stellar mass and star-formation activity across the redshift range $0.5\leq z\leq2.5$. We infer rest-frame near-IR S\'ersic profiles for $\approx 15.000$ galaxies in publicly available NIRCam imaging mosaics from the COSMOS-Web and PRIMER surveys. We augment these with rest-frame optical S\'ersic indices, previously measured from HST imaging mosaics. The median S\'ersic index evolves slowly or not at all with redshift, except for very high-mass galaxies ($M_\star > 10^{11}~{\text{M}}_\odot$), which show an increase from $n\approx 2.5$ to $n\approx 4$ at $z<1$. High-mass galaxies have higher $n$ than lower-mass galaxies ($M_\star=10^{9.5}~{\text{M}}_\odot$) at all redshifts, with a stronger dependence in the rest-frame near-IR than in the rest-frame optical at $z>1$. This wavelength dependence is caused by star-forming galaxies that have lower optical than near-IR $n$ at z>1 (but not at z<1). Both at optical and near-IR wavelengths, star-forming galaxies have lower $n$ than quiescent galaxies, fortifying the connection between star-formation activity and radial stellar mass distribution. At $z>1$ the median near-IR $n$ varies strongly with star formation activity, but not with stellar mass. The scatter in near-IR $n$ is higher in the green valley (0.25 dex) than on the star-forming sequence and among quiescent galaxies (0.18 dex) -- this trend is not seen in the optical because dust and young stars contribute to the variety in optical light profiles. Our newly measured rest-frame near-IR radial light profiles motivate future comparisons with radial stellar mass profiles of simulated galaxies as a stringent constraint on processes that govern galaxy formation.

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