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We derive the central stellar velocity dispersion function (VDF) for quiescent galaxies in 280 massive clusters with$\log (M_{200}/M_{\odot })>14$in IllustrisTNG300. The VDF is an independent tracer of the dark matter mass distribution of subhalos in galaxy clusters. Based on the IllustrisTNG cluster catalog, we select quiescent member subhalos with a specific star formation rate <2 × 10⁻¹¹yr⁻¹and stellar mass$\log (M_{*}/M_{\odot })>9$. We then simulate fiber spectroscopy to measure the stellar velocity dispersion of the simulated galaxies; we compute the line-of-sight velocity dispersions of star particles within a cylindrical volume that penetrates the core of each subhalo. We construct the VDFs for quiescent subhalos withinR₂₀₀. The simulated cluster VDF exceeds the simulated field VDF for$\log {\sigma }_{*}>2.2$, indicating the preferential formation of large velocity dispersion galaxies in dense environments. The excess is similar in simulations and in the observations. We also compare the simulated VDF for the three most massive clusters with$\log (M_{200}/M_{\odot })>15$with the observed VDF for the two most massive clusters in the local Universe, Coma and A2029. Intriguingly, the simulated VDFs are significantly lower for$\log {\sigma }_{*}>2.0$. This discrepancy results from (1) a smaller number of subhalos with$\log (M_{*}/M_{\odot })>10$in TNG300 compared to the observed clusters, and (2) a significant offset between the observed and simulatedM_*–σ_*relations. The consistency in the overall shape of the observed and simulated VDFs offers a unique window into galaxy and structure formation in simulations.

JWST has revealed a large population of UV-bright galaxies at $z\gtrsim 10$ and possibly overly massive galaxies at $z\gtrsim 7$, challenging standard galaxy formation models in the ΛCDM cosmology. We use an empirical galaxy formation model to explore the potential of alleviating these tensions through an Early Dark Energy (EDE) model, originally proposed to solve the Hubble tension. Our benchmark model demonstrates excellent agreement with the UV luminosity functions (UVLFs) at $4\lesssim z \lesssim 10$ in both ΛCDM and EDE cosmologies. In the EDE cosmology, the UVLF measurements at $z\simeq 12$ based on spectroscopically confirmed galaxies (eight galaxies at $z\simeq 11\!-\!13.5$) exhibit no tension with the benchmark model. Photometric constraints at $12 \lesssim z\lesssim 16$ can be fully explained within EDE via either moderately increased star-formation efficiencies ($\epsilon _{\ast}\sim 3\!-\!10\ \hbox{per cent}$ at $M_{\rm halo}\sim 10^{10.5}{\, \rm M_\odot }$) or enhanced UV variabilities ($\sigma _{\rm UV}\sim 0.8\!-\!1.3$ mag at $M_{\rm halo}\sim 10^{10.5}{\, \rm M_\odot }$) that are within the scatter of hydrodynamical simulation predictions. A similar agreement is difficult to achieve in $\Lambda$CDM, especially at $z\gtrsim 14$, where the required $\sigma _{\rm UV}$ exceeds the maximum value seen in simulations. Furthermore, the implausibly large cosmic stellar mass densities inferred from some JWST observations are no longer in tension with cosmology when the EDE is considered. Our findings highlight EDE as an intriguing unified solution to a fundamental problem in cosmology and the recent tensions raised by JWST observations. Data at the highest redshifts reached by JWST will be crucial for differentiating modified galaxy formation physics from new cosmological physics.

Fuzzy dark matter (FDM), comprised of ultralight ($m \sim 10^{-22}\,{\rm eV}$) boson particles, has received significant attention as a viable alternative to cold dark matter (CDM), as it approximates CDM on large scales (${\gtrsim}1$ Mpc) while potentially resolving some of its small-scale problems via kiloparsec-scale quantum interference. However, the most basic FDM model, with one free parameter (the boson mass), is subject to a tension: small boson masses yield the desired cores of dwarf galaxies but underpredict structure in the Lyman-α forest, while large boson masses render FDM effectively identical to CDM. This Catch-22 problem may be alleviated by considering an axion-like particle with attractive particle self-interactions. We simulate an idealized FDM halo with self-interactions parametrized by an energy decay constant $f \sim 10^{15}~\rm {GeV}$ related to the axion symmetry-breaking conjectured to solve the strong-CP problem in particle physics. We observe solitons, a hallmark of FDM, condensing within a broader halo envelope, and find that the density profile and soliton mass depend on self-interaction strength. We propose generalized formulae to extend those from previous works to include self-interactions. We also investigate a critical mass threshold predicted for strong interactions at which the soliton collapses into a compact, unresolved state. We find that the collapse happens quickly, and its effects are initially contained to the central region of the halo.

We make an in-depth analysis of different active galactic nuclei (AGN) jet models’ signatures, inducing quiescence in galaxies with a halo mass of 10¹²M_⊙. Three jet models, including cosmic-ray-dominant, hot thermal, and precessing kinetic jets, are studied at two energy flux levels each, compared to a jet-free, stellar feedback-only simulation. Each of our simulations is idealized isolated galaxy simulations with AGN jet powers that are constant in time and generated using GIZMO and with FIRE stellar feedback. We examine the distribution of Mgii, Ovi, and Oviiiions, alongside gas temperature and density profiles. Low-energy ions, like Mgii, concentrate in the interstellar medium (ISM), while higher energy ions, e.g., Oviii, prevail at the AGN jet cocoon’s edge. High-energy flux jets display an isotropic ion distribution with lower overall density. High-energy thermal or cosmic-ray jets pressurize at smaller radii, significantly suppressing core density. The cosmic-ray jet provides extra pressure support, extending cool and warm gas distribution. A break in the ion-to-mass ratio slope in Oviand Oviiiis demonstrated in the ISM-to-circumgalactic medium (CGM) transition (between 10 and 30 kpc), growing smoothly toward the CGM at greater distances.

At high redshifts (z≳ 12), the relative velocity between baryons and dark matter (the so-called streaming velocity) significantly affects star formation in low-mass objects. Streaming substantially reduces the abundance of low-mass gas objects while simultaneously allowing for the formation of supersonically induced gas objects (SIGOs) and their associated star clusters outside of dark matter halos. Here, we present a study of the population-level effects of streaming on star formation within both halos and SIGOs in a set of simulations with and without streaming. Notably, we find that streaming actually enhances star formation within individual halos of all masses at redshifts betweenz= 12 andz= 20. This is demonstrated both as an increased star formation rate per object as well as an enhancement of the Kennicutt–Schmidt relation for objects with streaming. We find that our simulations are consistent with some observations at high redshift, but on a population level, they continue to underpredict star formation relative to the majority of observations. Notably, our simulations do not include feedback and so can be taken as an upper limit on the star formation rate, exacerbating these differences. However, simulations of overdense regions (both with and without streaming) agree with observations, suggesting a strategy for extracting information about the overdensity and streaming velocity in a given survey volume in future observations.

JWST has revealed a large population of accreting black holes (BHs) in the early Universe. Recent work has shown that even after accounting for possible systematic biases, the high-z$M_*{\!-\!}M_{\rm \rm bh}$ relation can be above the local scaling relation by $\gt 3\sigma$. To understand the implications of these overmassive high-z BHs, we study the BH growth at $z\sim 4{\!-\!}7$ using the $[18~\mathrm{Mpc}]^3$BRAHMA cosmological simulations with systematic variations of heavy seed models that emulate direct collapse black hole (DCBH) formation. In our least restrictive seed model, we place $\sim 10^5~{\rm M}_{\odot }$ seeds in haloes with sufficient dense and metal-poor gas. To model conditions for direct collapse, we impose additional criteria based on a minimum Lyman Werner flux (LW flux $=10~J_{21}$), maximum gas spin, and an environmental richness criterion. The high-z BH growth in our simulations is merger dominated, with a relatively small contribution from gas accretion. The simulation that includes all the above seeding criteria fails to reproduce an overmassive high-z$M_*{\!-\!}M_{\rm bh}$ relation consistent with observations (by factor of $\sim 10$ at $z\sim 4$). However, more optimistic models that exclude the spin and environment based criteria are able to reproduce the observed relations if we assume $\lesssim 750~\mathrm{Myr}$ delay times between host galaxy mergers and subsequent BH mergers. Overall, our results suggest that current JWST observations may be explained with heavy seeding channels if their formation is more efficient than currently assumed DCBH conditions. Alternatively, we may need higher initial seed masses, additional contributions from lighter seeds to BH mergers, and / or more efficient modes for BH accretion.

We illuminate the altered evolution of galaxies in clusters compared to central galaxies by tracking galaxies in the IllustrisTNG300 simulation as they enter isolated clusters of mass 1013 < M200,mean/M⊙ < 1015 (at z = 0). We demonstrate significant trends in galaxy properties with residence time (time since first infall) and that there is a population of galaxies that remain star forming even many Gyr after their infall. By comparing the properties of galaxies at their infall time to their properties at z = 0, we show how scaling relations, like the stellar-to-halo mass ratio, shift as galaxies live in the cluster environment. Galaxies with a residence time of 10 Gyr increase their stellar-to-halo mass ratio, by around 1 dex. As measurements of the steepest slope of the galaxy cluster number density profile (Rst), frequently used as a proxy for the splashback radius, have been shown to depend strongly on galaxy selection, we show how Rst depends on galaxy residence time. Using galaxies with residence times less than one cluster crossing time (≈5 Gyr) to measure Rst leads to significant offsets relative to using the entire galaxy population. Galaxies must have had the opportunity to ‘splash back’ to the first caustic to trace out a representative value of Rst, potentially leading to issues for galaxy surveys using ultraviolet-selected galaxies. Our work demonstrates that the evolution of cluster galaxies continues well into their lifetime in the cluster and departs from a typical central galaxy evolutionary path.

Self-interacting dark matter (SIDM) is increasingly studied as a potential solution to small-scale discrepancies between simulations of cold dark matter (CDM) and observations. We examine a physically motivated two-state SIDM model with both elastic and inelastic scatterings. In particular, endothermic, exothermic, and elastic scattering have equal transfer cross-sections at high relative velocities ($v_{\rm rel}\gtrsim 400~{\rm km\, s}^{-1})$. In a suite of cosmological zoom-in simulation of Milky Way-size haloes, we vary the primordial state fractions to understand the impact of inelastic dark matter self-interactions on halo structure and evolution. In particular, we test how the initial conditions impact the present-day properties of dark matter haloes. Depending on the primordial state fraction, scattering reactions will be dominated by either exothermic or endothermic effects for high and low initial excited state fractions, respectively. We find that increasing the initial excited fraction reduces the mass of the main halo, as well as the number of subhaloes on all mass scales. The main haloes are cored, with lower inner densities and higher outer densities compared with CDM. Additionally, we find that the shape of the main halo becomes more spherical the higher the initial excited state fraction is. Finally, we show that the number of satellites steadily decreases with initial excited state fraction across all satellite masses.

We investigate galaxy sizes at redshift $z\gtrsim 6$ with the cosmological radiation-magnetohydrodynamic simulation suite thesan(-hr). These simulations simultaneously capture reionization of the large-scale intergalactic medium and resolved galaxy properties. The intrinsic sizes ($r^{\ast }_{1/2}$) of simulated galaxies increase moderately with stellar mass at $M_{\ast } \lesssim 10^{8}{\, \rm M_\odot}$ and decrease fast at larger masses, resulting in a hump feature at $M_{\ast }\sim 10^{8}{\, \rm M_\odot}$ that is insensitive to redshift. Low-mass galaxies are in the initial phase of size growth and are better described by a spherical shell model with feedback-driven outflows competing with the cold inflowing gas streams. In contrast, massive galaxies fit better with the disc formation model. They generally experience a phase of rapid compaction and gas depletion, likely driven by internal disc instability rather than external processes. We identify four compact quenched galaxies in the $(95.5\, {\rm cMpc})^{3}$ volume of thesan-1 at $z\simeq 6$ and their quenching follows reaching a characteristic stellar surface density akin to the massive compact galaxies at cosmic noon. Compared to observations, we find that the median ultraviolet effective radius ($R^{\rm UV}_{\rm eff}$) of simulated galaxies is at least three times larger than the observed ones at $M_{\ast }\lesssim 10^{9}{\, \rm M_\odot}$ or $M_{\rm UV}\gtrsim -20$ at $6 \lesssim z \lesssim 10$. The population of compact galaxies ($R^{\rm UV}_{\rm eff}\lesssim 300\, {\rm pc}$) galaxies at $M_{\ast }\sim 10^{8}{\, \rm M_\odot}$ is missing in our simulations. This inconsistency persists across many other cosmological simulations with different galaxy formation models and demonstrates the potential of using galaxy morphology to constrain physics of galaxy formation at high redshifts.