arXiv subjects

Corentin Cadiou

Publications and source records attributed to Corentin Cadiou.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting the Missing Baryon Problem: Baryon Redistribution Across Halo Evolution

The baryon fraction provides a fundamental diagnostic of baryonic matter distribution within dark matter halos and the baryon cycle. While its cosmic value is well constrained, the baryon content within halos on nearly all scales is significantly lower than the cosmic mean; this is called the ``missing baryon problem.'' Using the high spatial, mass, and temporal resolutions of the NewCluster simulation, we investigate the baryon fraction evolution by tracing halo assembly histories from merger trees and gas tracer particles. We identify three distinct evolutionary phases: an early growth phase driven by cold accretion in low-mass halos, a suppression phase likely dominated by supernova feedback, and a recovery phase in massive halos enabled by deeper potential wells and hot-mode accretion. We further find that the redshift dependence of baryon fraction, particularly in low-mass halos, is influenced by the thermal state of the intergalactic medium, with suppression emerging after the surrounding gas becomes persistently hotter than the halo virial temperature. In addition, the scatter in baryon fraction at fixed halo mass correlates with the large-scale environment, with baryon-rich halos preferentially residing closer to filamentary structures. Overall, our results highlight that baryon fraction evolution is governed by the interplay between feedback and environment, requiring a time-resolved perspective on the baryon cycle.

astro-ph.GA↗

arXiv2026

MEGATRON: Dwarf Galaxy Quenching in the Epoch of Reionization

Low-mass galaxies during the Epoch of Reionization are expected to form stars in short bursts separated by periods of inactivity, but what regulates this cycle, and how sensitive it is to the modelling of stellar feedback, remains unclear. We use the MEGATRON high-redshift zoom simulation suite, in which four star-formation and stellar-feedback prescriptions are evolved from identical initial conditions, to study the regulation of stellar mass growth in galaxies with $M_{*} \sim 10^{4} - 10^{8} M_{\odot}$ at $z = 8.5$. We classify galaxies as Star-Forming, Mini-Quenched (no significant star formation over the last 10 Myr), or Quenched (no significant star formation over the last 100 Myr). The feedback prescription controls both how often galaxies are quiescent and how this depends on mass. Models with stronger or more clustered feedback yield larger quiescent fractions compared to the fiducial and Varying IMF models. Duty cycles at fixed mass also differ by factors of several between models. The cold gas profiles of Quenched galaxies are consistent with two physically distinct modes of quenching: mechanical gas evacuation, producing compact, cold gas-poor systems, and thermodynamic suppression, retaining a cold but star-formation-inactive reservoir. At these masses, quiescent galaxies fall below un-lensed JWST/NIRCam detection limits, whereas star-forming galaxies of the same mass do not, and consequently flux-limited samples will be biased towards active phases. Measuring the quiescent fraction as a function of stellar mass in lensing fields would provide a direct test of stellar-feedback models at Cosmic Dawn.

astro-ph.GA↗

arXiv2026

Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon

Most of the mass and angular momentum of today's disk galaxies assembled at $z>1$. Yet, it remains unclear how these galaxies acquired their gas, how their baryons and dark matter coevolved, and how feedback and radial gas transport shaped their disks. Addressing these gaps requires resolved observations of cold gas, which carries most of the mass and angular momentum involved in galaxy assembly. By resolving CO and [C II] at kpc scales, ALMA revealed a surprising population of rotation-dominated disks, even at $z>2$, exhibiting kinematic signatures consistent with spiral arms, bars, and tidal tails. Yet, these studies are limited to massive ($M_\star>10^{10.5}$ M$_\odot$) and highly star-forming (SFRs$\gtrsim 100$ M$_\odot$yr$^{-1}$) galaxies, the progenitors of today's most massive elliptical and disk galaxies. To understand how most present-day spirals (like the Milky Way) assembled, it is crucial to resolve their low-mass progenitors, which dominate the star-forming galaxy population by number at $z>1$. Achieving this goal demands a tenfold increase in line sensitivity and hence a next-generation sub-/millimetre facility: ALMA2040. This leap in sensitivity will enable routine resolved studies of hundreds of $M_\star>10^9$ M$_\odot$ galaxies, including those on and below the main sequence of star-forming galaxies, providing representative, statistical galaxy samples with sub-kpc constraints on the cold gas kinematics and morphology. By uniquely providing resolved CO, [C I], and [C II] observations across $z=1-6$, ALMA2040 will trace a much larger fraction of the cold-gas reservoir than is accessible today, extending resolved studies from rare massive and/or lensed systems to representative galaxy populations. In this way, ALMA2040 will transform our understanding of how galaxy disks formed and evolved.

astro-ph.IM↗

arXiv2026

Early onset of the hot circumgalactic medium around Milky Way galaxies

Hot coronae are key regulators in Milky Way (MW)-type galaxy formation and are thought to emerge once a galaxy's dark matter halo crosses a critical mass threshold, $M_{\mathrm{vir}}\sim10^{12} {\mathrm{M}}_\odot$, so that accretion shocks can heat infalling gas to virial temperatures, $T_{\mathrm{vir}}$. Here we investigate the roles of stellar feedback and accretion shocks in establishing the circumgalactic medium (CGM) around MW-mass galaxies using the VINTERGATAN cosmological simulation suite. We find that stellar feedback drives the early formation of a hot CGM, with $T_{\mathrm{CGM}}\sim T_{\mathrm{vir}}$. By contrast, in feedback-free simulations, accretion shocks alone do not produce a CGM with comparably high average temperatures at early epochs ($z>2$), independent of gas metallicity. We show that CGM virialisation (defined when halo-gas cooling time exceeds the free-fall time) begins with the emergence of a hot corona ($T>10^5$ K) that can appear as early as $z\approx3$ at virial radius, $R_{\mathrm{vir}}$, when feedback is included. This is much earlier than predicted by accretion-shock theory or feedback-free models ($z\lesssim1$). While accretion shocks alone produce an inside-out virialisation pattern, feedback can alter this behaviour, driving a rapid transition ($\lesssim0.5$ Gyr) that is either outside-in or nearly simultaneous throughout the halo. Finally, these early-forming coronae are largely stable from formation through to the present day, but can appear to evolve simply because the definition of $R_{\mathrm{vir}}$ grows with time. This 'CGM pseudo-evolution' is analogous to the pseudo-evolution of dark matter haloes and should be taken into account when interpreting the evolution of hot coronae.

astro-ph.GA↗

arXiv2026

MEGATRON: The Physical Origins of Steep UV Slopes at High Redshift

The ultraviolet (UV) spectral slope, $β$, serves as a fundamental probe of stellar population properties and interstellar medium conditions in galaxies. At high redshift, a small sample of galaxies have been confirmed to have extremely blue spectral slopes of $β<-2.8$, as measured directly from spectroscopy. One explanation for such galaxies is that they are leaking copious amounts of ionizing photons such that these photons are never processed into the nebular continuum and we are observing the bluer intrinsic slopes of the stellar populations. Here, we use a detailed set of radiation hydrodynamics simulations with parsec-scale resolution and non-equilibrium chemistry to elucidate the physical origin of extremely blue UV slopes at high redshift. We show that, while some extremely blue galaxies (EBGs) do indeed have high escape fractions, a second population of EBGs has $f_{\rm esc}<1\%$. In this second population, the ISM gas densities tend to be much lower, and the timescale for ionization fronts to reach their Strömgren radii can be longer than the main-sequence lifetime of massive stars, leading to a lag in nebular emission. Our results demonstrate that extremely blue UV slopes do not uniquely imply high escape fractions, which highlights the importance of time-dependent (non-equilibrium) nebular emission for interpreting the spectra of galaxies in the early Universe.

astro-ph.GA↗

arXiv2026

MEGATRON: Reproducing the Diversity of High-Redshift Galaxy Spectra with Cosmological Radiation Hydrodynamics Simulations

We present the MEGATRON suite of cosmological radiation hydrodynamics simulations following the formation of Milky Way-mass galaxies from the earliest cosmic epochs when Population III stars form to Cosmic Noon. The suite represents the first set of cosmological simulations that couples a vast non-equilibrium thermochemistry network of primordial species, metals, and molecules to multifrequency, on-the-fly radiation transport, allowing us to directly predict the spectral properties of early galaxies. By initializing the simulations at zero metallicity, resolving haloes well below the atomic cooling threshold, reaching parsec-scale resolution, and modeling a Milky Way-mass environment, we aim to address four key science themes: 1) Star formation at cosmic dawn, 2) Galaxy formation and the interstellar medium in the epoch of reionization, 3) The circumgalactic medium towards cosmic noon, and 4) Reionization in a local volume environment and near-field cosmology. In this introductory work, we present an overview of the physical characteristics of high-redshift MEGATRON galaxies and their environment at $z>8$. We present a library of $>175,000$ simulated galaxy spectra and demonstrate how much of the diversity of galaxy spectra seen by JWST is naturally reproduced in the context of a $Λ$CDM cosmology. Caveats are discussed, such as the lack of AGN in our simulations and the limitations of our adopted stellar population and chemical yield models. This project represents a step towards making more direct comparisons between simulations and observations and is particularly applicable for optimizing methods to infer galaxy properties from existing high-redshift JWST spectra and imaging data.

astro-ph.GA↗

arXiv2026

MEGATRON: the impact of non-equilibrium effects and local radiation fields on the circumgalactic medium at cosmic noon

We present three cosmological radiation-hydrodynamic zoom simulations of the progenitor of a Milky Way-mass galaxy from the MEGATRON suite. The simulations combine on-the-fly radiative transfer with a detailed non-equilibrium thermochemical network (81 ions and molecules), resolving the cold and warm gas in the circumgalactic medium (CGM) on spatial scales down to 20 pc and on average 200 pc at cosmic noon. Comparing our full non-equilibrium calculation with local radiation to traditional post-processed photoionization equilibrium (PIE) models assuming a uniform UV background (UVB), we find that non-equilibrium physics and local radiation fields fundamentally impact the thermochemistry of the CGM. Recombination lags and local radiation anisotropy shift ions away from their PIE+UVB values and modify covering fractions (for example, HI damped Ly$α$ absorbers differ by up to 40%). In addition, a resolution study with cooling-length refinement allows us to double the resolution in the cold and warm CGM gas, reaching 120 pc on average. When refining on cooling length, the mass of the lightest cold clumps decreases tenfold to $\approx 10^4\,M_\odot$, their boundary layers develop sharper ion stratification, and the warm gas is better resolved, boosting the abundance of warm gas tracers such as CIV and OIII. Together, these results demonstrate that non-equilibrium thermochemistry coupled to radiative transfer, combined with physically motivated resolution criteria, is essential to predict circumgalactic absorption and emission signatures and to guide the design of targeted observations with existing and upcoming facilities.

astro-ph.GA↗

arXiv2026

MEGATRON: how the first stars can create an iron metallicity plateau in the smallest dwarf galaxies

We study the stellar mass-iron metallicity relation of dwarf galaxies in the new high-resolution MEGATRON cosmological radiation-hydrodynamics simulations. These simulations model galaxy formation up to $z\approx8$ in a region that will collapse into a Milky-Way-like galaxy at $z=0$, while self-consistently tracking Population III and II (Pop.~III, Pop.~II) star formation, feedback and chemical enrichment. MEGATRON dwarf galaxies are in excellent agreement with the observed stellar mass-metallicity relation at $z=0$, including an over-abundance of dwarfs along a flat plateau in metallicity ($\langle [\rm{Fe}/\rm{H}] \rangle \approx -2.5$) at low stellar masses ($M_{\star} \leq 10^5 \, \rm{M}_{\odot}$). We tie this feature to the chemical enrichment of dwarf galaxies by Pop.~III pair-instability supernova (PISN) explosions. The strong Lyman-Werner background (LW) from the protogalaxy ensures that PISNe occur in haloes massive enough ($\approx 10^7\, \rm{M}_{\odot}$) to retain their ejecta. We also predict a tail of $\approx 20\%$ of iron-deficient ($\langle [\rm{Fe}/\rm{H}] \rangle \leq - 3$) dwarf galaxies. We show that both plateau and tail (i) are robust to large variations in Pop.~II feedback assumptions, and (ii) survive in bound satellites surrounding the central galaxy at $z=0$.

astro-ph.GA↗

arXiv2026

The impact of evolving cosmic filaments on mass and spin evolution of dark matter halos

The evolution of galaxies is closely tied to that of their host dark matter halos, which is in turn strongly modulated by the surrounding large-scale environment. Cosmic filaments are expected to influence the peculiar motions, mass assembly and angular momentum of nearby halos through highly anisotropic matter flows. In order to fully capture the dynamic interplay between the filaments and halos, we develop an algorithm to trace the progenitors of individual filaments identified at z=0 with DisPerSE in a cosmological N-body simulation, by quantifying the spatial similarity between a descendant filament and progenitor candidates. This enables us to reconstruct filament-by-filament evolutionary histories, including their bulk drift and the evolution of density profiles, from which splashback radii and core overdensities are derived. Using these time-dependent properties, we re-examine halo phase-space trajectories in a filament-centric frame that evolves with time. This eliminates biases inherent to static models by separating halo motions from the motion of the filaments, allowing trajectories to be identified more reliably. We find that as halos approach high-density filaments, their mass accretion rates are systematically suppressed beginning at the filament outskirts, suggestive of tidal stripping or suppressed net accretion. Furthermore, the evolution of halo spin alignments exhibits a clear departure from stochastic random-walk expectations. This suggests that distinct mass flow regimes in and around filaments exert different torques on infalling halos, thereby changing their angular momentum. Our findings, derived from a sample screened for major mergers, highlight the pure dynamical impact of the filamentary environment. Ultimately, we demonstrate that tracking the simultaneous co-evolution of filaments and halos is essential for accurately characterizing environmental effects.

astro-ph.CO↗

arXiv2026

The causal effect of cosmic filaments on dark matter halos

The way in which the large-scale cosmic environment affects galactic properties is not yet understood. Dark matter halos, which embed galaxies, initially evolve following linear theory. Their subsequent evolution is driven by non-linear structure formation in the halo region and in its outer environment. In this work, we present the first study where we explicitly control the linear part of the evolution of the halo, thus revealing the role of non-linear effects on halo formation. We focus specifically on the effect of proximity to a large cosmological filament. We employ the splicing method to keep fixed the initial density, velocity, and potential fields where a halo will form while changing its outer environment, from an isolated state to one where the halo is near a large filament. In the regime of Milky Way-mass halos, we find that mass and virial radius of such halos are not affected by even drastic changes of environment, whereas halo spin and shape orientation with respect to a massive filament is largely impacted, with fluctuations of up to 80 % around the mean value. Our results suggest that halo orientation and shape cannot be predicted accurately from a local analysis in the initial conditions alone. This has direct consequences on the modeling of intrinsic alignment for cosmic shear surveys, like Euclid. Our results highlight that non-linear couplings to the large-scale environment may have an amplitude comparable to linear effects, and should thus be treated explicitly in analytical models of dark matter halo formation.

astro-ph.CO↗

arXiv2026

MEGATRON: The environments of Population III stars at Cosmic Dawn and their connection to present day galaxies

We present results of Pop. III formation in the MEGATRON suite of simulations, which self-consistently follows radiation and non-equilibrium chemistry, and resolves gas at near-pc resolution of a Milky Way-mass halo at Cosmic Dawn. While the very first Pop. III stars form in halos with masses well below the atomic cooling limit, whose cooling is dominated by molecular hydrogen, the majority of Pop. III stars form in more massive systems above the $10^4$~K atomic cooling threshold. The shift in cooling regime of halos hosting new Pop. III stars occurs within $100$ Myr of the first Pop. III star as the Lyman-Werner (LW) background rapidly increases to $10^{-21}\,\rm erg\,s^{-1}\,cm^{-2}\,Hz^{-1}\,sr^{-1}$. We find that the global Pop. III star formation rate stabilizes to a value of $10^{-3}\,\rm M_\odot\,yr^{-1}$ at $z=20$. Among the three processes that quench Pop. III star formation in mini-halos, the LW background, gas starvation, and external chemical enrichment, the LW background is most important. A small fraction of haloes undergo multiple episodes of Pop. III star formation when the earlier forming stars all directly collapse to black holes. If the halos become massive enough, they can form up to $\sim100$ Pop. III stars in a single burst, which may be observable by JWST with moderate gravitational lensing. Pop. III stars form at a wide range of distances from UV-bright galaxies, with only $0.06\%$ of Pop. III stars forming within the virial radius of galaxies with $M_{\rm UV} < -17$. Finally, by tracking Pop. III star remnants down to $z=0$, we find that $75-80\,$% reside in the stellar halo of our simulated Milky Way analogue, while the remainder are gravitationally bound to lower-mass systems, including satellite halos.

astro-ph.GA↗

arXiv2026

MEGATRON: Disentangling Physical Processes and Observational Bias in the Multi-Phase ISM of High-Redshift Galaxies

Now detected out to redshifts of $z\sim 14.5$, the rest-frame ultraviolet and optical spectra of galaxies encode numerous physical properties of the interstellar medium (ISM). Accurately extracting these properties from spectra remains a key challenge that numerical simulations are uniquely suited to address. We present a study of the observed ISM of galaxies in MEGATRON: a suite of cosmological radiation hydrodynamics simulations coupled to on-the-fly non-equilibrium thermochemistry, with multiple prescriptions for star formation/feedback and parsec-scale resolution; capable of directly predicting spectroscopic properties of early galaxies. We find that irrespective of feedback physics used, the ISM of high-redshift galaxies is denser, less metal enriched, and subject to higher ionization parameters and radiation fields compared to similar mass galaxies in the local Universe -- in agreement with interpretations of JWST observations. Using common observational techniques to infer bulk galaxy properties, we find that ISM gas density controls the slope of the mass-metallicity relation. Similarly, at the densities reached in some high-redshift galaxies, O32 becomes a density tracer rather than one of ionization parameter. This motivates the use of other line ratios like C43 and N43 to infer the ionization state of the gas. Finally, various feedback models populate different regions of strong-line diagnostic diagrams as the line ratios are sensitive to the feedback-modulated density-temperature structure of the ISM. Therefore, observed strong-line diagnostics can provide a strong constraint on the underlying physics of star formation and feedback in the high-redshift Universe.

astro-ph.GA↗

arXiv2026

The Impact of Star Formation and Feedback Recipes on the Stellar Mass and Interstellar Medium of High-Redshift Galaxies

We introduce MEGATRON, a new galaxy formation model for cosmological radiation hydrodynamics simulations of high-redshift galaxies. The model accounts for the non-equilibrium chemistry and heating/cooling processes of $\geq 80$ atoms, ions, and molecules, coupled to on-the-fly radiation transfer. We apply the model in a cosmological setting to the formation of a $10^9\ {\rm M_{\odot}}$ halo at $z=6$, and run 25 realizations at pc-scale resolution, varying numerous parameters associated with our state-of-the-art star formation, stellar feedback, and chemical enrichment models. We show that the overall budget of feedback energy is the key parameter that controls star formation regulation at high redshift, with other numerical parameters (e.g. supernova clustering, star formation conditions) having a more limited impact. As a similar feedback model has been shown to produce realistic $z=0$ galaxies, our work demonstrates that calibration at $z=0$ does not guarantee strong regulation of star formation at high-redshift. Interestingly, we find that subgrid model variations that have little impact on the final $z=6$ stellar mass can lead to substantial changes on the observable properties of high-redshift galaxies. For example, different star formation models based on, e.g. density thresholds or turbulence inspired criteria, lead to fundamentally distinct nebular emission line ratios across the interstellar medium (ISM). These results highlight the ISM as an important resource for constraining models of star formation, feedback, and galaxy formation in the JWST era, where emission line measurements for $>1,000$ high-redshift galaxies are now available.

astro-ph.GA↗

arXiv2025

On the Origin of Intracluster Light based on the High-resolution Simulation, NewCluster

Intracluster light (ICL) is a key component of galaxy clusters, with the potential to trace their dynamical assembly histories and the underlying dark matter distribution. Despite these prospects, its faint nature makes a consensus on its origin or population properties difficult to achieve, both in observations and simulations. In the hope of finding a breakthrough, we utilize the ongoing high-resolution cluster simulation, NewCluster. By classifying billions of particles in and around the cluster with a rigorous tracking procedure, we find that the majority of the ICL originates from satellites, including surviving and disrupted galaxies. Another notable finding is that the preprocessed component follows the density profile of dark matter better than the other components and has distinctive properties: old age, low metallicity, and enhanced $α$-element abundance. We further investigate the orbital dynamics, and our results demonstrate that the stripped fraction of satellites is primarily determined by the time since infall and the pericenter distance. By linking the demographic, chemical, and orbital properties of ICL stars to their origins, this work proposes a quantitative approach for tracing the assembly history of galaxy clusters from the ICL.

astro-ph.GA↗

arXiv2025

Introducing NewCluster: the first half of the history of a high-resolution cluster simulation

We introduce NewCluster, a new high-resolution cluster simulation designed to serve as the massive halo counterpart of the modern cosmological galaxy evolution framework. The zoom-in simulation targets a volume of $4.1σ$ overdensity region, which is expected to evolve into a galaxy cluster with a virial mass of $5 \times 10^{14} M_\odot$, comparable to that of the Virgo Cluster. The zoom-in volume extends out to 3.5 virial radii from the central halo. The novelties of NewCluster are found in its resolutions. Its stellar mass resolution of $2 \times 10^{4} M_\odot$ is effective for tracing the early assembly of massive galaxies as well as the formation of dwarf galaxies. The spatial resolution of 68 parsecs in the best-resolved regions in the adaptive-mesh-refinement approach is powerful to study the detailed kinematic structure of galaxies. The time interval between snapshots is also exceptionally short-15 Myr-which is ideal for monitoring changes in the physical properties of galaxies, particularly during their orbital motion within a larger halo. The simulation has up-to-date feedback schemes for supernovae and active galactic nuclei. The chemical evolution is calculated for ten elements, along with dust calculation that includes the formation, size change, and destruction. To overcome the limitations of the Eulerian approach used for gas dynamics in this study, we employ Monte Carlo-based tracer particles in NewCluster, enabling a wide range of scientific investigations.

astro-ph.GA↗

arXiv2025

EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations

We present a new suite of EDGE (`Engineering Dwarfs at Galaxy formation's Edge') cosmological zoom simulations. The suite includes 15 radiation-hydrodynamical dwarf galaxies covering the ultra-faint to the dwarf irregular regime ($10^4 \leq M_{\star}(z=0) \leq 10^8 \, M_{\odot}$) to enable comparisons with observed scaling relations. Each object in the suite is evolved at high resolution ($\approx 3 \, \text{pc}$) and includes stellar radiation, winds and supernova feedback channels. We compare with previous \textsc{edge} simulations without radiation, finding that radiative feedback results in significantly weaker galactic outflows. This generalizes our previous findings to a wide mass range, and reveals that the effect is most significant at low $M_{\star}$. Despite this difference, stellar masses stay within a factor of two of each other, and key scaling relations of dwarf galaxies (size-mass, neutral gas-stellar mass, gas-phase mass-metallicity) emerge correctly in both simulation suites. Only the stellar mass -- stellar metallicity relation is strongly sensitive to the change in feedback. This highlights how obtaining statistical samples of dwarf galaxy stellar abundances with next-generation spectrographs will be key to probing and constraining the baryon cycle of dwarf galaxies.

astro-ph.GA↗

arXiv2025

How complex are galaxies? A non-parametric estimation of the intrinsic dimensionality of wide-band photometric data

Galaxies are complex objects, yet the number of independent parameters to describe them remains unknown. We present here a non-parametric method to estimate the intrinsic dimensionality of large datasets. We apply it to wide-band photometric data drawn from the COSMOS2020 catalogue and a comparable mock catalogue from the Horizon-AGN simulation. Our galaxy catalogues are limited in signal-to-noise ratio in all optical and NIR bands. Our results reveal that most of the variance in the wide-band photometry of this galaxy sample can be described with at most $4.3\pm0.5$ independent parameters for star-forming galaxies and $2.9\pm0.2$ for passive ones, both in the observed and simulated catalogues. We identify one of these parameters to be noise-driven, and recover that stellar mass and redshift are two key independent parameters driving the magnitudes. Our findings support the idea that wide-band photometry does not provide more than one additional independent parameter for star-forming galaxies. Although our sample is not mass-limited and may miss some passive galaxies due to our cut in SNR, our work suggests that dimensionality reduction techniques may be effectively used to explore and analyse wide-band photometric data, provided the used latent space is at least four-dimensional.

astro-ph.GA↗

arXiv2025

EDGE-INFERNO: Simulating every observable star in faint dwarf galaxies and their consequences for resolved-star photometric surveys

Interpretation of data from faint dwarf galaxies is made challenging by observations limited to only the brightest stars. We present a major improvement to tackle this challenge by undertaking zoomed cosmological simulations that resolve the evolution of all individual stars more massive than $0.5\,{\rm M}_{\odot}$, thereby explicitly tracking all observable stars for the Hubble time. For the first time, we predict observable color-magnitude diagrams and the spatial distribution of $\approx 100,000$ stars within four faint ($M_{\star} \approx 10^5 \, \,{\rm M}_{\odot}$) dwarf galaxies directly from their cosmological initial conditions. In all cases, simulations predict complex light profiles with multiple components, implying that typical observational measures of structural parameters can make total V-band magnitudes appear up to 0.5 mag dimmer compared to estimates from simulations. Furthermore, when only small ($\lessapprox100$) numbers of stars are observable, shot noise from realizations of the color-magnitude diagram introduces uncertainties comparable to the population scatter in, e.g., total magnitude, half-light radius, and mean iron abundance measurements. Estimating these uncertainties with fully self-consistent mass growth, star formation and chemical enrichment histories paves the way for more robust interpretation of dwarf galaxy data.

astro-ph.GA↗