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Mark Vogelsberger

Publications and source records attributed to Mark Vogelsberger.

At least 19 recordsLinked to original sources
arXiv2026

What becomes of JWST/NIRCam-selected high-redshift massive galaxies?

Early JWST/NIRCam surveys revealed a puzzling population of high-redshift massive galaxy candidates largely absent from previous rest-frame UV surveys. Spectroscopic follow-up has both confirmed and contested these candidates, whose potential overabundance may challenge traditional models of galaxy formation. In this study we evaluate the reliability of the photometric selections used to identify these candidates in observational data by applying them to galaxies in the TNG300 simulation with synthetic dust-attenuated photometry. Among the five observational selection criteria considered, we find that the selection presented by Pérez-González et al. is the most reliable and inclusive. Nevertheless, only 1 of the 18 galaxies at $z\sim5$ with $M_{\star} \geq 10^{11}~\mathrm{M_{\odot}}$ in the simulation satisfies this selection; the remaining 17 galaxies are on average $\sim0.5$ mag bluer than the color selection under the adopted dust model. We construct an improved JWST/NIRCam color-magnitude selection that provides a more complete census of massive galaxies at $z\sim5$ in TNG300 while excluding dusty, low-mass galaxies identified by criteria from the observational literature. We investigate the descendants of the most massive NIRCam-selected galaxies at $z=7,~4,$ and $2$ in TNG300, finding that they rarely evolve into the most massive galaxies by $z=0$. In general only the high-redshift massive galaxies that undergo substantial late-time ($z\lesssim0.2$) merger-driven growth become the most massive galaxies in the Universe today. Together these results suggest that current observational JWST/NIRCam selections are not identifying the most massive high-redshift galaxies, and caution against interpreting high-redshift massive galaxies as direct progenitors of the most massive galaxies at $z=0$.

astro-ph.GA↗
arXiv2026

Resolving the thermal component of stellar feedback with the "anchor-and-refine" scheme in galactic simulations

(abridged) Stellar feedback regulates galactic baryon cycles, but galaxy-scale simulations often cannot resolve supernova cooling radii. Momentum-based subgrid models can consequently underresolve the hot gas around young stars. We develop an "anchor-and-refine" feedback scheme that anchors a host cell near each star particle, preventing its displacement and preserving a thermal-feedback reservoir. When the cooling radius is resolved, all supernova energy is injected into the host cell as thermal energy; otherwise, the host cell is refined and terminal momentum is deposited into surrounding gas cells. Idealized tests agree with high-resolution simulations, yielding consistent superbubble properties and preserving hot interiors without artificial cooling. In an isolated Milky Way-mass galaxy, the scheme captures finer X-ray-emitting structures and a sharply defined, X-ray-bright central mid-plane. It also produces a smoother star formation history than pure hybrid feedback. Hot gas dominates outflow mass loading, with the mass-loading factor plateauing at approximately 0.2 at heights z>1 kpc. Phase decomposition indicates that hot gas sustains a steady, energy-driven wind, whereas cooler outflows decline with height because of radiative cooling and gravitational fallback. These results highlight the role of thermal feedback in driving galactic winds. By preserving hot superbubble interiors and the partition of thermal and kinetic energy, anchor-and-refine improves the treatment of hot gas, star formation, and feedback at limited resolution, supporting future applications to galaxy-scale and cosmological zoom-in simulations.

astro-ph.GA↗
arXiv2026

NORI: a GPU-accelerated code for simulating self-gravitating and self-interacting dark matter

Self-interacting dark matter (SIDM) can form cores in dark matter haloes and later drive their gravothermal collapse, raising their central densities far above those of NFW haloes. Simulating this collapse is computationally demanding, requiring increasingly short time-steps and a large particle number to resolve the shrinking core. We present NORI, an $N$-body code that runs on CPUs and GPUs and simulates isolated self-gravitating systems with elastic, isotropic self-interactions using a Monte-Carlo method. To avoid MPI communication in the tree walks, each compute node in CPU mode, and each GPU or group of GPUs in GPU mode, holds a copy of all particles and its own Morton-ordered tree. A fixed evaluation order makes the results bitwise identical on CPUs and GPUs. Applying scattering events sequentially conserves the momentum and energy of each pair to round-off and allows multiple scatterings per particle per step. With global time-steps in both codes, NORI is several times faster on CPUs than our AREPO-2 implementation. One four-A100 GPU node is up to 60 times faster per time-step than AREPO-2 on a 112-core CPU node. For a full core-collapse simulation, where AREPO-2 uses individual time-steps, the speed-up is $\sim 30$ for the central density to reach $10^3$--$10^4$ times the NFW scale density, $ρ_{\rm s}$. We follow a halo with $10^8$ particles within $r_{200}$ to a central density of $10^4\,ρ_{\rm s}$. Within the limit of about $2\times10^9$ particles set by data replication, NORI provides an efficient tool for isolated SIDM simulations, including gravothermal collapse and cluster collisions.

astro-ph.IM↗
arXiv2026

Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations

We establish a unified theory-to-simulation framework for self-interacting dark matter (SIDM) that integrates three components: (i) a comprehensive, self-contained treatment of its particle-physics foundations and a broad range of model classes; (ii) a systematic, quantitative mapping from microscopic dark-sector physics to structure-formation simulation inputs through explicit expressions and numerical prescriptions; and (iii) the development, implementation, and validation of a broad suite of SIDM algorithms and a dedicated DM decay module in the moving-mesh code AREPO-2. Under (i), we detail the particle content, symmetries, interactions, production mechanisms, and constraints of a broad landscape of elementary and composite SIDM models, and present representative viable benchmark models. Under (ii), the mapping specifies cosmological initial conditions, internal-state masses and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative energy loss, and decay rates and recoil kinematics. We then apply this mapping to a broad range of SIDM model classes. Under (iii), we implement and validate SIDM algorithms with constant and velocity-dependent cross sections, covering isotropic and anisotropic scattering, multi-state elastic and inelastic reactions, and dissipative processes, alongside a dedicated DM decay module in AREPO-2. We validate these implementations through beam-lattice deflection experiments, thermalization and uniform-box decay tests, isolated-halo gravothermal core-collapse simulations, and cosmological box and zoom-in simulations. These tests recover analytical predictions, establish agreement across numerical schemes, and reproduce published benchmarks. Our theory-to-simulation framework serves as a cross-disciplinary reference and a practical bridge between SIDM particle physics and simulations of nonlinear structure formation.

astro-ph.CO↗
arXiv2026

The THESAN-ZOOM project: the delayed rise of Lyman continuum escape fractions in bursty high-redshift galaxies

The ionizing radiation that galaxies release into their surroundings depends on whether efficient Lyman continuum (LyC) escape coincides with strong photon production. Stellar feedback can open escape paths as the source population fades, linking the escaping radiation to a galaxy's recent history. We investigate this timing in thirteen high-redshift (z > 3) target haloes from the THESAN-ZOOM radiation-hydrodynamic simulations, post-processed with COLT radiative transfer and sampled at ~10 Myr intervals. The clearest delayed relationship links $\text{SFR}_{10}/\text{SFR}_{100}$ to the LyC escape fraction. Selecting the nearest positive cross-correlation peak gives typical lags of ~16 Myr and peak correlations of 0.4-0.6 in massive haloes, with longer and less coherent delays towards lower masses. The fitted delays scale approximately as $M_\star^{-0.19}$ and $M_\text{halo}^{-0.27}$, although the shortest lags approach the native snapshot spacing. Recurrent variations span multiple amplitude-dependent timescales, consistent with repeated episodes of star formation and feedback. Recent star formation closely tracks both intrinsic and escaping photon rates, while the escape fraction reflects the evolving gas transparency. The H$α$-to-UV luminosity ratio retains a delayed association with escape, offering an observable connection between burst phase and leakage. High transparency during a fading phase can nevertheless yield little escaping radiation. The temporal overlap of photon production and transmission therefore shapes both the amount and timing of escaping radiation, informing the interpretation of observed leakers and their contribution to cosmic reionization.

astro-ph.GA↗
arXiv2026

Wandering intermediate-mass black holes and off-nuclear tidal disruption events from early star clusters

Off-nuclear tidal disruption events (TDEs) reveal evidence for massive black holes outside galactic centers, but the origins of this wandering population remain uncertain. We investigate wandering intermediate-mass black holes (IMBHs) formed through runaway stellar collisions in dense, high-redshift star clusters and predict their TDE signatures across cosmic time. Our semi-analytic model samples clusters associated with low-mass subhalos at $7<z<20$ and uses merger trees from the IllustrisTNG TNG50 simulation to follow the assembly of 15 elliptical galaxies with stellar masses of $10^9-10^{11}~M_\odot$. We compare two models for high-redshift cluster formation: a maximal model taken from a high-resolution simulation and a conservative model calibrated from local cluster relations. Off-nuclear TDEs produced through this mechanism occur in bursts within 10-100 Myr of IMBH formation as the loss-cone surrounding the black hole is depleted. We estimate the rate of off-nuclear TDEs expected across time per galaxy, and characterize these events as typically occurring between $10-10^3$ kpc from their host galaxy centers. Event rates increase with galaxy mass; in the maximal model, the progenitors of the most massive galaxies reach peak off-nuclear TDE rates of approximately $5\times10^{-4}-4\times10^{-2}~\mathrm{yr}^{-1}$ per galaxy at $7\lesssim z\lesssim13$. This work provides a framework for constraining the early population of star clusters that form IMBHs through runaway collapse via their contribution to the rate of off-nuclear TDEs in the high redshift Universe.

astro-ph.GA↗
arXiv2026

TNGC-SIDM I: Evolution of massive cluster mergers under the self-interacting dark matter paradigm

Merging galaxy clusters provide an ideal laboratory for testing the self-interacting nature of dark matter. In this paper, we present a pilot study of magnetohydrodynamical cosmological zoom-in simulations of two cluster mergers selected from TNG-Cluster, with $M_{\rm 200c} \sim 9\times10^{14}~M_\odot$ and $M_{\rm 200c}\sim 2\times10^{14}~M_\odot$. The simulations are performed with both standard collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM), assuming an isotropic, velocity-independent cross-section of $σ_{\rm T}/m_χ= 1~\rm cm^2~g^{-1}$, with an additional $0.5~\rm cm^2~g^{-1}$ run for the low-mass system, and the mass resolution and galaxy formation model are unchanged from TNG-Cluster. We show how dark matter self-interactions produce an isothermal core in the dark matter halo, generate unique substructures in the intracluster light, and introduce variation in the multi-wavelength observables of the intracluster plasma. Using these simulations, we test the validity of observational probes for dark matter self-interactions in cluster mergers. We find that the shock-to-shock separation shows similar evolution in the self-interaction models tested here, providing a reference for distinguishing the $\sim100-200~\rm kpc$-scale difference in halo separation induced by self-interactions. Moreover, the dark matter halo centroid of the main cluster in the massive cluster merger is offset from the brightest cluster galaxy by as much as $\sim20~\rm kpc$, larger than the offset in the sub-cluster. This offset persists beyond 4 Gyr after the first pericenter passage. Our results indicate that sample selection plays a key role in testing the possible self-interacting nature of dark matter using cluster mergers, and that double radio relic cluster mergers and massive clusters with evidence of an ancient major merger offer a promising testbed for this purpose.

astro-ph.CO↗
arXiv2026

The Lumina Project: Intergalactic Clumping and Recombination Sinks

Recombinations during the Epoch of Reionization are intrinsically inhomogeneous, with different regions of the intergalactic medium contributing unevenly depending on their density, temperature, ionization state, and spatial patchiness. We combine the high- and medium-resolution 95.5 cMpc Thesan-1 andh Thesan-2 runs with the significantly larger 500 cMpc Lumina simulation to measure clumping factors and recombination rates consistently across different resolutions and box sizes. We consider the standard ionized hydrogen clumping factor, $C_{\rm HII} \equiv \langle n_{\rm HII}^2\rangle/\langle n_{\rm HII}\rangle^2$, and a recombination-weighted clumping factor, $C_{\rm rec}$. Despite differences in resolution, volume, and reionization history, the simulations show an approximately universal clumping evolution at the 10-20% level when parametrized by the global ionized fraction $x_{\rm HII}$ rather than by redshift. Across all simulations, $C_{\rm rec}$ remains systematically below $C_{\rm HII}$, with the discrepancy increasing toward lower redshift as photoheating suppresses recombinations. In \lumina, the density-only prescription overpredicts the instantaneous recombination rate by factors of 1.29 at $z\approx8$ and 1.84 at $z\approx5$, and the cumulative recombination count by a factor of 1.45 by $z\approx5$. Mapping the recombination budget in the joint overdensity-temperature plane reveals that the dominant recombination ridges closely follow simple analytic thermal equilibrium bands. Finally, we introduce a phase-space recombination integral and define a phase-space clumping factor, $C_{\rm ps}(Δ,T)$, which isolates the intrinsic recombination enhancement associated with ionization structure and thermal state at fixed overdensity and temperature.

astro-ph.GA↗
arXiv2026

A Consistent Implementation of Cluster Strong Lensing in Cosmological Simulation Light Cones

Galaxy cluster strong gravitational lensing plays a central role in precision cosmology, yet robust theoretical predictions have lagged behind an abundance of high-quality strong lensing observations. This shortfall reflects both a mismatch between the geometry of the strong-lensing problem and standard cubic simulation boxes, and the fundamental tension between simulation volume and resolution. Consequently, many current forecasts adopt hybrid approaches that extract individual lenses from simulations and combine them with analytic or observed source populations positioned near caustics. These methods often omit correlated and/or uncorrelated line-of-sight (LoS) structure, or include it in ways that do not preserve correlations across redshift. Here we present a fully simulation-based procedure that generates strong-lensing images directly from particle data, drawing the lens, source, and all intervening resolved objects self-consistently from the simulated large-scale structure. Our approach combines a structure-preserving remapping of the simulation volume into a lensing-appropriate geometry with multi-plane ray tracing, enabling the use of uniform simulation boxes that resolve both cluster-scale primary lenses and high-redshift source galaxies. We demonstrate the method by generating example light cones and images using IllustrisTNG data, then use these results to conservatively quantify the impact of LoS structure on image configurations and critical-curve morphology. We find that uncorrelated LoS structure can shift the relative positions of lensed images by several arcseconds, introduces a $\sim 6\%$ scatter in the area of a cluster's primary critical curve, and changes the total critical area within 100$^{\prime\prime}$ of the cluster potential minimum by $16^{+20\%}_{-14\%}$ at a source plane redshift of $z_s=4$.

astro-ph.CO↗
arXiv2026

Galaxy and Halo Assembly Bias in Alternative Dark Matter Models

The clustering of dark matter halos depends not only on halo mass but also on secondary halo properties, a phenomenon known as halo assembly bias. Coupled with variations in halo occupation, this dependence impacts galaxy clustering, an effect termed galaxy assembly bias. While previous studies have found only weak cosmological dependence of assembly bias within the $Λ$CDM framework, its sensitivity to the underlying dark matter physics remains largely unexplored. We use the matched dark-matter-only and hydrodynamical simulations from the AIDA-TNG suite to measure assembly bias across four dark matter models: cold dark matter, warm dark matter, and self-interacting dark matter with constant cross-sections and velocity-dependent cross-sections. We find that at z = 0, halo assembly bias is nearly identical across the four models for concentration-selected halos, as is the concentration dependence of the halo occupation distribution. The resulting galaxy assembly bias signals likewise show only weak model dependence. For stellar-mass-selected galaxy samples with $n = 0.0586 h^{3} Mpc^{-3}$ at z = 0, the velocity-dependent self-interacting dark matter scenario exhibits the largest deviation from the fiducial cold dark matter model: its assembly bias contribution to galaxy clustering is enhanced by up to $\sim 6\%$, corresponding to a $\sim 3\%$ difference in the assembly bias amplitude. Although statistically distinguishable, this difference is small and unlikely to be detected in current analyses. The weak model dependence persists across different galaxy number densities and redshifts. Overall, within the TNG galaxy-formation framework, these results indicate that assembly bias is largely insensitive to the dark matter models explored here, providing a robust baseline for future studies of the galaxy-halo connection in alternative dark matter scenarios.

astro-ph.CO↗
arXiv2026

The Entangling of Supernova Feedback Impacts with Coarsening Simulation Resolution

It is often understood that supernova (SN) feedback in galaxies is responsible for regulating star formation (SF) and generating gaseous outflows. However, a detailed look at the small-scale effects of SNe on the interstellar medium (ISM) in simulations shows that the macroscopic processes of SF suppression and outflow generation proceed in distinct channels. We demonstrate this finding in two independent simulations of isolated dwarf galaxies with very high (m_gas ~ Msun) numerical resolution, LYRA and RIGEL. Our findings suggest that the macroscopic effect of a given SN on the galaxy is best predicted by its local density. Outflows are driven by SNe in diffuse regions expanding to their cooling radii on large (~kpc) scales, while dense SF regions are disrupted in a localized (~pc) manner. However, these separate feedback channels are only distinguishable at very high resolutions capable of following mass scales \lesssim 10^2 \msun. When averaging on coarser scales, ISM densities are greatly mis-estimated, and variations between different SF and SNe-affected regions are severely washed out. It therefore cannot be __self-consistently__ determined, from coarse-resolution information __alone__, (1) whether a SN tends to contribute to outflows or direct SF suppression, and (2) the rate of SF in a given region. In particular, commonly used parameters in coarse-resolution (subgrid) models, such as the SN cooling radius and SF density threshold, may require more detailed treatments informed by high-resolution studies.

astro-ph.GA↗
arXiv2026

The Lumina Project: Morphology of Ionized Bubbles and Neutral Islands

The Epoch of Reionization is characterized by the nucleation, expansion, and percolation of ionized bubbles in the intergalactic medium. Interpreting emerging multi-wavelength observations from facilities such as JWST and next-generation 21 cm interferometers requires a detailed theoretical understanding of the 3D morphology of these HII regions and of the residual neutral structures that survive near the end of reionization. We analyze the geometry and physical properties of ionized bubbles and late-time neutral islands in the large-volume 500 Mpc$^3$ radiation-hydrodynamics simulation Lumina. We identify discrete structures with a 3D watershed method and measure their volumes, shape tensors, and internal gas properties. The volume-weighted bubble size distributions evolve substantially across the EoR: characteristic radii shift from Reff~1 cMpc at z>10 to Reff>100 cMpc by z< 6, while watershed-derived sizes exceed line-of-sight mean-free-path measurements by roughly a factor of 3 at intermediate redshifts. The bulk bubble population is predominantly prolate through most of the EoR. By z~6, however, the volume-weighted distribution of the triaxiality parameter T, which distinguishes flattened from elongated structures, becomes bimodal in the fiducial segmentation, with a sharp oblate peak near T~0.25 associated with a small number of very large bubbles during late percolation. The properties of bubble interiors are consistent with inside-out reionization, with median gas overdensities within bubbles decreasing from $δ$~1 at z=15 toward the cosmic mean by z=6. Beyond a minimum near the resolution scale, the median internal UV radiation energy density increases with bubble size. The residual neutral islands at z< 6 peak in volume-weighted size near Reff~10 cMpc and remain predominantly prolate, consistent with anisotropic residual neutral structure near the end of reionization.

astro-ph.CO↗
arXiv2026

From starlight to dark matter: a stochastic interpolation approach to map dark matter from stellar density

The dark matter halo profile in galaxies holds key information about the nature of dark matter and galaxy formation. Constraining the dark matter profile of galaxies beyond the Milky Way traditionally requires expensive spectroscopic observations for kinematic information. In this paper, we explore a conditional generative model framework to map the dark matter profile of Milky Way-mass galaxies from stellar density profiles, more easily obtainable through large photometric imaging surveys. As a proof of concept, we train the model to learn a stochastic bridge between instrument systematics-free baryonic stellar distributions and underlying dark matter density maps from the DREAMS hydrodynamics simulation suite. We recover 2D dark matter density profiles with a typical accuracy of $\sim0.1$ dex ($\sim1.5$% of the truth in log scale). The stochastic sampling procedure provides uncertainty estimates of the predicted dark matter map, with typical values $\sim0.1$ dex. Out-of-domain tests with Milky Way-mass galaxies from IllustrisTNG and FIRE simulations show that, while the model can qualitatively be generalized to TNG50 galaxies from IllustrisTNG, the model is sensitive to the galaxy formation model, with $\sim0.2$-$0.4$ dex over-prediction for the inner profiles ($r\lesssim5$ kpc) of the FIRE test galaxies. Future work will explore training with additional suites of simulations and/or conditioning on additional information, such as multi-band images. Our results are a first step towards using generative models as a flexible, uncertainty-aware framework for turning forthcoming data from large imaging surveys into spatially resolved dark matter maps.

astro-ph.GA↗
arXiv2026

Radiative Feedback in Population III Protostellar Growth: HI Shielding and HII Region Trapping

We present a suite of radiation-magnetohydrodynamics simulations from the Popsicle project that follow the long-term growth ($\sim 50$ kyr) of primordial protostars while self-consistently coupling radiation, turbulence, and magnetic fields. The simulation suite is designed to quantify the relative impacts of the pathways of radiative feedback in Pop III stars -- the extreme-ultraviolet (EUV) ionization and Lyman-Werner (LW) dissociation -- by considering simulations with/without their inclusion. We find that without HI shielding, LW feedback can suppress and ultimately terminate accretion. With HI shielding, the large column densities near the protostar significantly weaken LW feedback. In the polar direction, atomic hydrogen fully shields LW radiation where H$_2$ self-shielding alone is insufficient. This leads to lower gas temperatures near the protostar and higher accretion rates, yielding larger final stellar masses than in models without shielding. The HII region remain confined, extending $\sim$100 AU beyond the sink accretion radius (75 AU), as dense gravitationally bound gas sustains high recombination rates and prevents sustained pressure-driven breakout. Turbulence and magnetic fields may also contribute to its confinement, even at high ionizing luminosities. These results demonstrate that the interplay of gas dynamics, shielding, and radiative feedback can significantly alter the growth of Pop III stars. We discuss the implications for the initial mass function of primordial stars and the influence of feedback from early stellar populations.

astro-ph.GA↗
arXiv2026

Gas distributions inside and around haloes in the alternative dark matter simulations AIDA-TNG

The nature of Dark Matter (DM) is one of the greatest mysteries of modern astrophysics. While the standard Cold DM (CDM) model successfully explains observations on most astrophysical scales, DM particles have not yet been detected, leaving room for a plethora of different models. In order to identify their observable signatures, we use the AIDA-TNG cosmological simulation suite to predict the distributions of gas and neutral hydrogen (HI) in the CDM, Self-Interacting DM (SIDM), velocity-dependent SIDM (vSIDM), and Warm DM (WDM) models. We find that the DM models investigated have very limited impact on the median gas and HI profiles of haloes. Nevertheless, for the most massive haloes ($M_{\rm vir}\sim10^{14}\,\mathrm{M}_\odot$), we find that DM self-interactions can reduce the central potential, thereby lowering gravitational heating and the central gas temperature. We find that, in all models, the halo-to-halo variation in the HI profiles is explained by AGN feedback, and that the specific characteristics of the DM model are largely subdominant. Nevertheless, we detect some systematic difference in the case of SIDM, with more HI surviving close to the centre with respect to other models. We provide fitting functions for the gas and HI profiles. We investigate the galaxy-Ly$α$ cross-correlation function (\galacc) for different halo masses, redshifts and observational strategies. We find that at $z=0$ vSIDM can be distinguished from CDM in haloes with $10^{12}\lesssim M_{\rm vir}\lesssim10^{13}\,{\rm M}_\odot$, while SIDM1 can be distinguished from CDM in haloes with $M_{\rm vir}\gtrsim10^{13}\,{\rm M}_\odot$. We estimate that statistically-robust detection requires sampling $\sim160$ haloes with $\sim20$ sightlines each, a task that can be achieved with current and future facilities like WEAVE, 4MOST, PFS, ELT and WST.

astro-ph.GA↗
arXiv2026

RIGEL: Ultra-faint dwarf galaxy diversity shaped by inhomogeneous cosmic reionization

Ultra-faint dwarf galaxies (UFDs) are among the smallest and oldest galaxies in the Universe and are widely regarded as relics of cosmic reionization. To investigate how reionization quenches star formation and shapes the diversity of UFDs, we present a suite of eight cosmological zoom-in simulations of isolated UFDs with present-day halo masses of $\sim10^9\,{\rm M}_\odot$. The simulations are performed with the radiation-magnetohydrodynamic galaxy formation framework Realistic ISM modeling in Galaxy Evolution and Lifecycles (RIGEL), coupled to realistic large-scale radiation fields extracted from the THESAN reionization simulation. Despite residing in similar $z=0$ halos, the simulated galaxies span nearly two orders of magnitude in stellar mass and broadly reproduce the observed luminosities, sizes, metallicities, and stellar kinematics of Local Group UFDs. We find that reionization quenches star formation through a two-stage process. The arrival of the ionization front rapidly photoionizes the diffuse circumgalactic and intergalactic gas, suppressing further gas accretion onto the galaxy. Star formation nevertheless continues for several hundred Myr using the surviving self-shielded gas reservoir and ceases only after this gas is consumed or dispersed. Within 500 Myr after reionization, less than 40% of the initial gas mass remains in the halo, with photoevaporation constituting the dominant gas-loss channel. We further show that the halo mass at the time of reionization is a key parameter governing the subsequent evolution of UFDs. Galaxies residing in more massive halos at reionization retain gas for longer periods and undergo more extended chemical enrichment. Consequently, the halo mass at reionization strongly correlates with the final stellar mass, stellar age spread, and chemical evolution of the galaxy.

astro-ph.GA↗
arXiv2026

Weighing Little Red Dots with Transient Events

Recent JWST observations have revealed a large population of compact red sources at $z \gtrsim 4$, known as Little Red Dots (LRDs), many of which show signatures of accreting massive black holes (BHs). The physical nature of these sources and their connection to host galaxies are under debate. We propose an independent avenue for constraining their nature through transient phenomena, such as tidal disruption events (TDEs) and quasi-periodic eruptions (QPEs), arising from interactions between a star and the gas envelope surrounding the BH. These event rates depend sensitively on BH mass and provide a way to "weigh" LRDs. We calculate the expected TDE and QPE rates in LRDs under three distinct scenarios: (1) LRDs are truly overmassive BHs, (2) LRDs have BH masses following the classical local scaling relations (and the reported BH masses in observations are overestimated), and (3) the currently observed LRDs are only the tip of the iceberg of a larger population of low-mass BHs. We find that the predicted TDE and QPE rates differ dramatically across scenarios, especially in the presence of steep stellar cusps. The expected TDE rates per degree-square, assuming a Hernquist stellar distribution with a Bahcall-Wolf cusp embedded, are $2.78 \times 10^{-3}$, $1.96 \times 10^{-3}$, and $3.37 \times 10^{-2} \, {\rm yr}^{-1} \, {\rm deg}^{-2}$ for the three scenarios, respectively, while the QPE rates are $1.64 \times 10^{-2}$, $4.72 \times 10^{-2}$, and $4.96 \times 10^{-1} \, {\rm yr}^{-1} \, {\rm deg}^{-2}$. Upcoming wide-field surveys with Euclid, Roman, and LSST may be capable of detecting these high-redshift transient events and obtaining light curves, which encode additional information about the BH mass and the gas structure of LRDs. Stellar transient events will provide valuable insight into the early assembly of massive BHs.

astro-ph.GA↗
arXiv2026

Host Dependence and Line-of-Sight Effects on Galaxy-Galaxy Strong Lensing in Clusters

The cross section for galaxy-galaxy strong lensing (GGSL) events in galaxy clusters has repeatedly been found to be higher in observations than in cosmological simulations. We revisit this discrepancy using updated simulation methodology and investigate the dependence of the GGSL probability, $P_{\rm GGSL}$, on host-cluster lensing properties, baryonic physics, and correlated and uncorrelated line-of-sight structure. We find that correlated material within $\sim 35$ cMpc of the cluster along the line of sight enhances $P_{\rm GGSL}$ by a few percent for typical systems and by up to $\sim15\%$ for the most efficient lenses. At fixed cluster mass, dark-matter-only simulations yield GGSL probabilities up to an order of magnitude lower than hydrodynamical simulations. We also find a strong dependence on the host-cluster Einstein radius, with an approximate scaling $P_{\rm GGSL} \propto θ_{\rm E}^{2}$. Matching simulated and observed clusters in both mass and Einstein radius seems to reduce the discrepancy relative to previous comparisons. However, our analysis does not clearly resolve the GGSL discrepancy, as the inferred tension depends strongly on the field-of-view definition: square fields are approximately consistent with simulations, while cluster member-bounded fields yield observed probabilities a factor of $\sim 2-3$ higher. Until observations and simulations share a matched selection function and matched measurement methodology, the residual tension cannot be cleanly attributed to either astrophysics or cosmology.

astro-ph.CO↗