Search

Observations of Faraday rotation and synchrotron emission in galaxy clusters imply large-scale magnetic fields with $\mu\mathrm{G}$ strengths possibly extending back to $z=4$. Non-radiative cosmological simulations of galaxy clusters show a comparably slow magnetic field growth that only saturates at late times. We include galaxy formation physics and find a significantly accelerated magnetic field growth. We identify three crucial stages in the magnetic field evolution. 1) At high redshift, the central dominant galaxy serves as the prime agent that magnetizes not only its immediate vicinity but also most of the forming protocluster through a combination of a small-scale dynamo induced by gravitationally driven, compressive turbulence and stellar and active galactic nuclei feedback that distribute the magnetic field via outflows. 2) This process continues as other galaxies merge into the forming cluster in subsequent epochs, thereby transporting their previously amplified magnetic field to the intracluster medium (ICM) through ram pressure stripping and galactic winds. 3) At lower redshift, gas accretion and frequent cluster mergers trigger additional small-scale dynamo processes, thereby preventing the decay of the magnetic field and fostering the increase of the magnetic coherence scale. We show that the magnetic field observed today in the weakly collisional ICM is consistently amplified on collisional scales. Initially, this occurs in the collisional interstellar medium during protocluster assembly, and later in the ICM on the magnetic coherence scale, which always exceeds the particle mean free path, supporting the use of magneto-hydrodynamics for studying the cluster dynamo. We generate synthetic Faraday rotation measure observations of protoclusters, highlighting the potential for studying magnetic field growth during the onset of cluster formation at cosmic dawn., Comment: 23 pages, 15 figures, submitted to A&A

AGN bubbles in cool-core galaxy clusters are believed to significantly facilitate the transport of cosmic ray electrons (CRe) throughout the cluster. Recent radio observations are revealing complex morphologies of cluster diffuse emission, potentially linked to interactions between AGN bursts and the cluster environment. We perform three-dimensional magneto-hydrodynamical simulations of binary cluster mergers and inject a bi-directional jet at the center of the main cluster. Kinetic, thermal, magnetic and CRe energy are included in the jet and we use the two-fluid formalism to model the CRe component. We explore a wide range of cluster merger and jet parameters. We discuss the formation of various wide-angle-tail (WAT) and X-shaped sources in the course of the early evolution of the jet and merger. During the last phase of the evolution, we find that the CR material efficiently permeates the central region of the cluster reaching radii of $\sim1$--2 Mpc within $\sim5$--6 Gyr, depending on the merger mass ratio. We find that solenoidal turbulence dominates during the binary merger and explore the possibility for the CRe jet material to be re-accelerated by super-Alfv\`enic turbulence and contribute to cluster scale radio emission. We find that the emission can be volume-filing, $\gtrsim 70$\%. Finally, we study the merger shock interaction with the CRe material and show that it is unlikely that this material significantly contributes to the radio relic emission associated with the shocks. We suggest that multiple jet outbursts and/or off-center radio galaxies would increase the likelihood of detecting these merger shocks in the radio due to shock re-acceleration., Comment: 29 pages, 18 figures, submitted to ApJ, comments welcome

JWST has recently revealed a large population of accreting black holes (BHs) in the early Universe. Even after accounting for possible systematic biases, the high-z $M_*-M_{\rm \rm bh}$ relation derived from these objects by Pacucci et al. (2023 P23 relation) is above the local scaling relation by $>3\sigma$. To understand the implications of potentially overmassive high-z BH populations, we study the BH growth at $z\sim4-7$ using the $[18~\mathrm{Mpc}]^3$ BRAHMA suite of 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 $\sim10^5~M_{\odot}$ seeds in halos 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. For the most restrictive simulation that includes all the above seeding criteria for DCBH formation, the high-z $M_*-M_{\rm bh}$ relation falls significantly below the P23 relation (by factor of $\sim10$ at $z\sim4$). Only by excluding the spin and environment based criteria, and by assuming $\lesssim750~\mathrm{Myr}$ delay times between host galaxy mergers and subsequent BH mergers, are we able to reproduce the P23 relation. Overall, our results suggest that if high-z BHs are indeed systematically overmassive, assembling them would require more efficient heavy seeding channels, higher initial seed masses, additional contributions from lighter seeds to BH mergers, and / or more efficient modes for BH accretion., Comment: 21 pages, 15 figures

We analyze ionized gas emission lines in deep rest-frame optical spectra of 16 quiescent galaxies at redshift $1.7

Massive quiescent galaxies in the young universe are expected to be quenched rapidly, but it is unclear whether they all experience starbursts before quenching and what physical mechanism drives rapid quenching. We study 16 massive quiescent galaxies ($\log(M_\star/M_\odot) > 10$) at $z\sim2$ selected from a representative sample of the Blue Jay survey. We reconstruct their star formation histories by fitting spectral energy distribution models to the JWST/NIRSpec $R\sim1000$ spectra. We find that massive quiescent galaxies can be split into three categories with roughly equal numbers of galaxies according to their SFHs: 1) Relatively old galaxies quenched at early epochs; 2) Galaxies that are rapidly and recently quenched after a flat or bursty formation history (depending on the assumed prior); 3) Galaxies that are rapidly and recently quenched after a major starburst. Most recently quenched galaxies show neutral gas outflows, probed by blueshifted $\rm Na\,I\,D$ absorption, and ionized gas emission, with line ratios consistent with active galactic nucleus (AGN) diagnostics. This suggests that AGN activity drives multi-phase gas outflows, leading to rapid quenching. By tracing back the SFHs of the entire sample, we predict the number density of massive quiescent galaxies at $z=4-6$: $n=3.0\pm1.4\times10^{-5}\,\rm Mpc^{-3}$. The two oldest massive quiescent galaxies in our sample appear to have extremely early formation and quenching ($z\gtrsim6$), possibly descendants of early post-starbursts at $z>3$. These galaxies still show neutral gas reservoirs and low-level star formation, consistent with weak H$\alpha$ emission, perhaps because the ejective AGN feedback that caused rapid quenching has weakened over time., Comment: Submitted to ApJ; 21 pages, 9 figures, 3 tables (excluding appendix)

The first "seeds" of supermassive black holes (BH) can range from $\sim10^2-10^6~M_{\odot}$. However, the lowest mass seeds ($\lesssim10^3 M_{\odot}$) are inaccessible to most cosmological simulations due to resolution limitations. We present our new BRAHMA suite of cosmological simulations that uses a novel flexible seeding approach to represent low mass seeds. Our suite consists of two types of boxes that model $\sim10^3~M_{\odot}$ seeds using two distinct but mutually consistent seeding prescriptions at different simulation resolutions. First, we have the highest resolution $[9~\mathrm{Mpc}]^3$ (BRAHMA-9-D3) boxes that directly resolve $\sim10^3~M_{\odot}$ seeds and place them within halos with dense and metal poor gas. Second, we have lower-resolution and larger-volume $[18~\mathrm{Mpc}]^3$ (BRAHMA-18-E4) and $\sim[36~\mathrm{Mpc}]^3$ (BRAHMA-36-E5) boxes that seed their smallest resolvable $\sim10^4~\&~10^5~\mathrm{M_{\odot}}$ BH descendants using new stochastic seeding prescriptions calibrated using the BRAHMA-9-D3 results. The three boxes together probe BHs between $\sim10^3-10^7 M_{\odot}$ at $z>7$ and we predict their key observables. The variation in the AGN luminosity functions is small (factors of $\sim2-3$) at the anticipated detection limits of potential future X-ray facilities ($\sim10^{43} \mathrm{ergs~s^{-1}}$ at $z\sim7$). Our simulations predict BHs $\sim10-100$ times heavier than expectations from local $M_*$ vs $M_{bh}$ relations, consistent with several JWST-detected AGN. For different seed models, our simulations merge BH binaries at $\sim1-15~\mathrm{kpc}$, with rates of $\sim200-2000$ per year for $\gtrsim10^3 M_{\odot}$ BHs, $\sim6-60$ per year for $\gtrsim10^4~M_{\odot}$ BHs, and up to $\sim10$ per year amongst $\gtrsim10^5 M_{\odot}$ BHs. These results suggest that the LISA mission has promising prospects for constraining seed models., Comment: 26 pages, 22 figures

We use deep JWST/NIRSpec R~1000 slit spectra of 113 galaxies at 1.7 < z < 3.5, selected from the mass-complete Blue Jay survey, to investigate the prevalence and typical properties of neutral gas outflows at cosmic noon. We detect excess Na I D absorption (beyond the stellar contribution) in 46% of massive galaxies ($\log$ M$_*$/M$_\odot >$ 10), with similar incidence rates in star-forming and quenching systems. Half of the absorption profiles are blueshifted by at least 100 km/s, providing unambiguous evidence for neutral gas outflows. Galaxies with strong Na I D absorption are distinguished by enhanced emission line ratios consistent with AGN ionization. We conservatively measure mass outflow rates of 3 - 100 $M_\odot$ yr$^{-1}$; comparable to or exceeding ionized gas outflow rates measured for galaxies at similar stellar mass and redshift. The outflows from the quenching systems (log(sSFR)[yr$^{-1}$] $\lesssim$ -10) have mass loading factors of 4 - 360, and the energy and momentum outflow rates exceed the expected injection rates from supernova explosions, suggesting that these galaxies could possibly be caught in a rapid blowout phase powered by the AGN. Our findings suggest that AGN-driven ejection of cold gas may be a dominant mechanism for fast quenching of star formation at z~2., Comment: 17 pages, 8 figures, accepted for publication in MNRAS

The intracluster medium of the Perseus Cluster exhibits spiral-shaped X-ray surface brightness discontinuities known as ``cold fronts'', which simulations indicate are caused by the sloshing motion of the gas after the passage of a subcluster. Recent observations of Perseus have shown that these fronts extend to large radii. In this work, we present simulations of the formation of sloshing cold fronts in Perseus using the AREPO magnetohydrodynamics code, to produce a plausible scenario for the formation of the large front at a radius of 700 kpc. Our simulations explore a range of subcluster masses and impact parameters. We find that low-mass subclusters cannot generate a cold front that can propagate to such a large radius, and that small impact parameters create too much turbulence which leads to the disruption of the cold front before it reaches such a large distance. Subclusters which make only one core passage produce a stable initial front that expands to large radii, but without a second core passage of the subcluster other fronts are not created at a later time in the core region. We find a small range of simulations with subclusters with mass ratios of $R \sim 1:5$ and initial impact parameter of $\theta~\sim~20-25^\circ$ which not only produce the large cold front but a second set in the core region at later times. These simulations indicate that the ``ancient' cold front is $\sim$6-8.5 Gyr old. For the simulations providing the closest match with observations, the subcluster has completely merged into the main cluster., Comment: 24 pages, 16 figures, submitted to ApJ

The nature of the first seeds of supermassive black holes (SMBHs) is currently unknown, with postulated initial masses ranging from $\sim10^5~M_{\odot}$ to as low as $\sim10^2~M_{\odot}$. However, most existing cosmological simulations resolve BHs only down to $\sim10^5-10^6~M_{\odot}$. In this work, we introduce a novel sub-grid BH seed model that is directly calibrated from high resolution zoom simulations that can trace the formation and growth of $\sim 10^3~M_{\odot}$ seeds forming in halos with pristine, star-forming gas. We trace the BH growth along merger trees until their descendants reach masses of $\sim10^4$ or $10^5~M_{\odot}$. The descendants assemble in galaxies with a broad range of properties (e.g., halo masses $\sim10^7-10^9~M_{\odot}$) that evolve with redshift and are sensitive to seed parameters. The results are used to build a new stochastic seeding model that directly seeds these descendants in lower resolution versions of our zoom region. Remarkably, we find that by seeding the descendants simply based on total galaxy mass, redshift and an environmental richness parameter, we can reproduce the results of the detailed gas based seeding model. The baryonic properties of the host galaxies are well reproduced by the mass-based seeding criterion. The redshift-dependence of the mass-based criterion captures the influence of halo growth, star formation and metal enrichment on seed formation. The environment based seeding criterion seeds the descendants in rich environments with higher numbers of neighboring galaxies. This accounts for the impact of unresolved merger dominated growth of BHs, which produces faster growth of descendants in richer environments with more extensive BH merger history. Our new seed model will be useful for representing a variety of low mass seeding channels within next generation larger volume uniform cosmological simulations., Comment: 26 pages, 17 figures

Large-scale outflows driven by supermassive black holes are thought to play a fundamental role in suppressing star formation in massive galaxies. However, direct observational evidence for this hypothesis is still lacking, particularly in the young universe where star formation quenching is remarkably rapid, thus requiring effective removal of gas as opposed to slow gas heating. While outflows of ionized gas are commonly detected in massive distant galaxies, the amount of ejected mass is too small to be able to suppress star formation. Gas ejection is expected to be more efficient in the neutral and molecular phases, but at high redshift these have only been observed in starbursts and quasars. Here we report JWST spectroscopy of a massive galaxy experiencing rapid quenching at redshift z=2.445. We detect a weak outflow of ionized gas and a powerful outflow of neutral gas, with a mass outflow rate that is sufficient to quench the star formation. Neither X-ray or radio activity are detected; however, the presence of a supermassive black hole is suggested by the properties of the ionized gas emission lines. We thus conclude that supermassive black holes are able to rapidly suppress star formation in massive galaxies by efficiently ejecting neutral gas., Comment: 21 pages, 9 figures. Published in Nature

We present the to-date largest parameter space exploration of binaries in circumbinary disks (CBDs), deriving orbital evolution prescriptions for eccentric, unequal mass binaries from our suite of hydrodynamic simulations. In all cases, binary eccentricities evolve towards steady state values that increase with mass ratio, and saturate at an equilibrium eccentricity $e_{\rm b, eq} \sim 0.5$ in the large mass ratio regime, in line with resonant theory. For binaries accreting at their combined Eddington limit, a steady state eccentricity can be achieved within a few Megayears. Once at their steady state eccentricities, binaries with $q_{\rm b} \gtrsim 0.3$ evolve towards coalescence, while lower mass ratio systems expand due to CBD torques. We discuss implications for population studies of massive black hole binaries, protostars in binary systems, and post-common envelope binaries observed by ground-based gravitational wave detectors., Comment: 12 pages, 8 figures. Submitted to MNRAS

Arkenstone is a new model for multiphase, stellar feedback driven galactic winds designed for inclusion in coarse resolution cosmological simulations. In this first paper of a series, we describe the features that allow Arkenstone to properly treat high specific energy wind components and demonstrate them using idealised non-cosmological simulations of a galaxy with a realistic CGM, using the Arepo code. Hot, fast gas phases with low mass loadings are predicted to dominate the energy content of multiphase outflows. In order to treat the huge dynamic range of spatial scales involved in cosmological galaxy formation at feasible computational expense, cosmological volume simulations typically employ a Lagrangian code or else use adaptive mesh refinement with a quasi-Lagrangian refinement strategy. However, it is difficult to inject a high specific energy wind in a Lagrangian scheme without incurring artificial burstiness. Additionally, the low densities inherent to this type of flow result in poor spatial resolution. Arkenstone addresses these issues with a novel scheme for coupling energy into the ISM/CGM transition region which also provides the necessary level of refinement at the base of the wind. In the absence of our improvements, we show that poor spatial resolution near the sonic point of a hot, fast outflow leads to an underestimation of gas acceleration as the wind propagates. We explore the different mechanisms by which low and high specific energy winds can regulate the SFR of galaxies. In future work, we will demonstrate other aspects of the Arkenstone model., Comment: Published MNRAS, 27 pages, 17 figures; updated for consistency with journal version

Feedback driven by jets from active galactic nuclei is believed to be responsible for reducing cooling flows in cool-core galaxy clusters. We use simulations to model feedback from hydrodynamic jets in isolated halos. While the jet propagation converges only after the diameter of the jet is well resolved, reliable predictions about the effects these jets have on the cooling time distribution function only require resolutions sufficient to keep the jet-inflated cavities stable. Comparing different model variations, as well as an independent jet model using a different hydrodynamics code, we show that the dominant uncertainties are the choices of jet properties within a given model. Independent of implementation, we find that light, thermal jets with low momentum flux tend to delay the onset of a cooling flow more efficiently on a $50$ Myr timescale than heavy, kinetic jets. The delay of the cooling flow originates from a displacement and boost in entropy of the central gas. If the jet kinetic luminosity depends on accretion rate, collimated, light, hydrodynamic jets are able to reduce cooling flows in halos, without a need for jet precession or wide opening angles. Comparing the jet feedback with a `kinetic wind' implementation shows that equal amounts of star formation rate reduction can be achieved by different interactions with the halo gas: the jet has a larger effect on the hot halo gas while leaving the denser, star forming phase in place, while the wind acts more locally on the star forming phase, which manifests itself in different time-variability properties., Comment: 22 pages, 20 figures, accepted for publication in MNRAS, comments welcome

We analyze the stellar abundances of massive galaxies ($\log M_\ast/M_\odot>10.5$) at $z=2$ in the IllustrisTNG simulation with the goal of guiding the interpretation of current and future observations, particularly from the James Webb Space Telescope. We find that the effective size, $R_e$, of galaxies strongly affects the abundance measurements: both [Mg/H] and [Fe/H] are anti-correlated with $R_e$, while the relative abundance [Mg/Fe] slightly increases with $R_e$. The $\alpha$ enhancement as tracked by [Mg/Fe] traces the formation timescale of a galaxy weakly, and mostly depends on $R_e$. Aperture effects are important: measuring the stellar abundances within 1~kpc instead of within $R_e$ can make a large difference. These results are all due to a nearly universal, steeply declining stellar abundance profile that does not scale with galaxy size -- small galaxies appear metal-rich because their stars live in the inner part of the profile where abundances are high. The slope of this profile is mostly set by the gas-phase abundance profile and not substantially modified by stellar age gradients. The gas-phase abundance profile, in turn, is determined by the strong radial dependence of the gas fraction and star formation efficiency. We develop a simple model to describe the chemical enrichment, in which each radial bin of a galaxy is treated as an independent closed-box system. This model reproduces the gas-phase abundance profile of simulated galaxies, but not the detailed distribution of their stellar abundances, for which gas and/or metal transport are likely needed., Comment: 16 pages, 12+2 figures, accepted for publication in MNRAS

We present a post-processing catalog of globular clusters (GCs) for the $39$ most massive groups and clusters in the TNG50 simulation of the IlllustrisTNG project (virial masses $M_{200} =[5\times 10^{12} \rm - 2 \times 10^{14}$] M$_{\odot}$). We tag GC particles to all galaxies with stellar mass $M_* \geq 5\times10^6$ M$_{\odot}$, and we calibrate their masses to reproduce the observed power-law relation between GC mass and halo mass for galaxies with $M_{200} \geq 10^{11}$ M$_{\odot}$ (corresponding to $M_* \sim 10^9$ $M_{\odot}$). Here we explore whether an extrapolation of this $M_{\rm GC}$-$M_{200}$ relation to lower-mass dwarfs is consistent with current observations. We find a good agreement between our predicted number and specific frequency of GCs in dwarfs with $\rm M_*=[5 \times 10^6 \rm - 10^9]$ M$_{\odot}$ and observations. Moreover, we predict a steep decline in the GC occupation fraction for dwarfs with $M_*<10^9$ M$_{\odot}$ which agrees well with current observational constraints. This declining occupation fraction is due to a combination of tidal stripping in all dwarfs plus a stochastic sampling of the GC mass function for dwarfs with $M_* < 10^{7.5}$ M$_{\odot}$. Our simulations also reproduce available constraints on the abundance of intra-cluster GCs in Virgo and Centaurus A. These successes provide support to the hypothesis that the $M_{\rm GC}$-$M_{200}$ relation holds, albeit with more scatter, all the way down to the regime of classical dwarf spheroidals in these environments. Our GC catalogs are publicly available as part of the IllustrisTNG data release., Comment: 16 pages, 8 figures (main body of paper). Resubmitted to MNRAS after positive referee report. The globular cluster catalogs for the 39 most massive groups and clusters in TNG50 are available for download from the IllustrisTNG public data release at www.tng-project.org/doppel22

One of the main limitations in precision cluster cosmology arises from systematic errors and uncertainties in estimating cluster masses. Using the Mock-X pipeline, we produce synthetic X-ray images and derive cluster and galaxy group X-ray properties for a sample of over 30,000 simulated galaxy groups and clusters with $M_{\rm 500crit}$ between $10^{12}$ and $2\times 10^{15}$ M$_{\odot}$ in IllustrisTNG. We explore the similarities and differences between IllustrisTNG predictions of the Sunyaev-Zel'dovich and X-ray scaling relations with mass. We find a median hydrostatic mass bias $b = 0.125 \pm 0.003$ for $M_{\rm 500crit}$ $>10^{13}$ M$_{\odot}$. The bias increases to $b = 0.17 \pm 0.004$ when masses are derived from synthetic X-ray observations. We model how different underlying assumptions about the dependence of $Y_{\rm X}$ on halo mass can generate biases in the observed $Y_{\rm SZ} - M_{Y_{\rm X}}$ scaling relation. In particular, the simplifying assumption that $Y_{\rm X} - M_{\rm tot}$ is self-similar at all mass scales largely hides the break in $Y_{\rm SZ} - M_{\rm tot}$ and overestimates $Y_{\rm SZ}$ at galaxy and groups scales. We show that calibrating the $Y_{\rm X}-$mass proxy using a new model for a smoothly broken power law reproduces the true underlying $Y_{\rm SZ} - M_{\rm tot}$ scaling relation with high accuracy. Moreover, $M_{Y_{\rm X}}$ estimates calibrated with this method lead to $Y_{\rm SZ} - M_{Y_{\rm X}}$ predictions that are not biased by the presence of lower mass clusters or galaxy groups in the sample. Finally, we show that our smoothly broken power law model provides a robust way to derive the $Y_{\rm X}-$mass proxy, significantly reducing the level of mass bias for clusters, groups, and galaxies., Comment: 12 pages, 5 figures; submitted to MNRAS. This is a companion paper to Pop et al. 2022: "Sunyaev-Zel'dovich effect and X-ray scaling relations of galaxies, groups and clusters in the IllustrisTNG simulations"

Observable thermodynamical properties of the intracluster medium (ICM) reflect the complex interplay between AGN feedback and the gravitational collapse of haloes. Using the large volume TNG300 simulation of the IllustrisTNG project we provide predictions for X-ray and Sunyaev-Zel'dovich (SZ) scaling relations for a sample of over 30,000 haloes that cover a wide mass range from galaxies to massive galaxy clusters ($M_{\rm 500crit}$ $\in [10^{12}$ M$_{\odot} - 2\times 10^{15}$ M$_{\odot}$]). We produce mock X-ray observations of simulated haloes using methods that are consistent with observational techniques. Thus, we investigate the scaling relations between the soft-band X-ray luminosity, spectroscopic temperature, gas mass fraction, $Y_{\rm X}$ and $Y_{\rm SZ}$ as a function of halo mass, and we find broad agreement between IllustrisTNG and the observed relations. Our results highlight the scatter and bias introduced by estimated masses, and thus the importance of converting simulated ICM properties to the observable space when comparing simulations to current X-ray observations. The wide range of halo masses in our sample provides new insights into the shape of the X-ray and SZ scaling relations across three orders of magnitude in mass. Our findings show strong evidence for a break in $z=0$ scaling relations. We introduce a smoothly broken power law model which robustly captures the location of this break, the width of the transition region around the break, as well as the slope dependence on halo mass. Our results inform the next generation of subgrid black hole feedback models and provide predictions for ongoing and future observational surveys., Comment: 29 pages, 15 figures, 7 tables, 2 appendices; submitted to MNRAS. This is a companion paper to Pop et al. 2022: "Unifying Sunyaev-Zel'dovich and X-ray predictions from clusters to galaxy groups: the impact of X-ray mass estimates on the Y-M scaling relation"

We explore implications of a range of black hole (BH) seeding prescriptions on the formation of the brightest $z\gtrsim6$ quasars in cosmological hydrodynamic simulations. The underlying galaxy formation model is the same as in IllustrisTNG. Using constrained initial conditions, we study the growth of BHs in rare overdense regions (forming $\gtrsim10^{12}M_{\odot}/h$ halos by $z=7$) using a $(9~\mathrm{Mpc}/h)^3$ simulated volume. BH growth is maximal within halos that are compact and have a low tidal field. For these halos, we consider an array of gas-based seeding prescriptions wherein $M_{\mathrm{seed}}=10^4-10^6~M_{\odot}/h$ seeds are inserted in halos above critical thresholds for halo mass and dense, metal-poor gas mass (defined as $\tilde{M}_{\mathrm{h}}$ and $\tilde{M}_{\mathrm{sf,mp}}$, respectively, in units of $M_{\mathrm{seed}}$). We find that a seed model with $\tilde{M}_{\mathrm{sf,mp}}=5$ and $\tilde{M}_{\mathrm{h}}=3000$ successfully produces a $z\sim6$ quasar with $\sim10^9~M_{\odot}$ mass and $\sim10^{47}~\mathrm{ergs~s^ {-1}}$ luminosity. BH mergers play a crucial role at $z\gtrsim9$, causing an early boost in BH mass at a time when accretion-driven BH growth is negligible. When more stringent seeding conditions are applied (for e.g., $\tilde{M}_{\mathrm{sf,mp}}=1000$), the relative paucity of BH seeds results in a much lower merger rate. In this case, $z\gtrsim6$ quasars can only be formed if we enhance the maximum allowed BH accretion rates (by factors $\gtrsim10$) compared to the accretion model used in IllustrisTNG. This can be achieved either by allowing for super-Eddington accretion, or by reducing the radiative efficiency. Our results show that progenitors of $z\sim6$ quasars have distinct BH merger histories for different seeding models, which will be distinguishable with LISA observations., Comment: 21 pages, 15 figures

The diffuse medium in and around galaxies can exist in a multi-phase state: small, cold gas clouds contributing significantly to the total mass embedded in pressure equilibrium with a hotter, more diffuse volume-filling component. Modeling this multi-phase state in cosmological simulations poses a significant challenge due to the requirements to spatially resolve the clouds and consequently the interactions between the phases. In this paper, we present a novel method to model this gas state in cosmological hydrodynamical simulations. We solve the compressible two-fluid hydrodynamic equations using a moving-mesh finite-volume method and define mass, momentum and energy exchange terms between the phases as operator-split source terms. Using a stratified flow model, our implementation is able to maintain volume fraction discontinuities in pressure equilibrium to machine precision, allowing for the treatment of both resolved and unresolved multi-phase fluids. The solver remains second order accurate on smooth hydrodynamics problems. We use the source and sink terms of an existing two-phase model for the interstellar medium to demonstrate the value of this type of approach in simulations of galaxy formation, compare it to its effective equation of state implementation, and discuss its advantages in future large-scale simulations of galaxy formation., Comment: 16 pages, 19 figures, accepted in MNRAS, comments welcome

Heating from active galactic nuclei (AGN) is thought to stabilize cool-core clusters, limiting star formation and cooling flows. We employ radiative magneto-hydrodynamic (MHD) simulations to model light AGN jet feedback with different accretion modes (Bondi-Hoyle-Lyttleton and cold accretion) in an idealised Perseus-like cluster. Independent of the probed accretion model, accretion efficiency, jet density and resolution, the cluster self-regulates with central entropies and cooling times consistent with observed cool-core clusters in this non-cosmological setting. We find that increased jet efficiencies lead to more intermittent jet powers and enhanced star formation rates. Our fiducial low-density jets can easily be deflected by orbiting cold gaseous filaments, which redistributes angular momentum and leads to more extended cold gas distributions and isotropic bubble distributions. In comparison to our fiducial low momentum-density jets, high momentum-density jets heat less efficiently and enable the formation of a persistent cold-gas disc perpendicular to the jets that is centrally confined. Cavity luminosities measured from our simulations generally reflect the cooling luminosities of the intracluster medium (ICM) and correspond to averaged jet powers that are relatively insensitive to short periods of low-luminosity jet injection. Cold gas structures in our MHD simulations with low momentum-density jets generally show a variety of morphologies ranging from discy to very extended filamentary structures. In particular, magnetic fields are crucial to inhibit the formation of unrealistically massive cold gas discs by redistributing angular momentum between the hot and cold phases and by fostering the formation of elongated cold filaments that are supported by magnetic pressure., Comment: 26 pages, 19 figures, published in MNRS

We study gas inflows onto supermassive black holes using hydrodynamics simulations of isolated galaxies and idealized galaxy mergers with an explicit, multiphase interstellar medium (ISM). Our simulations use the recently developed ISM and stellar evolution model called Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE). We implement a novel super-Lagrangian refinement scheme that increases the gas mass resolution in the immediate neighborhood of the black holes (BHs) to accurately resolve gas accretion. We do not include black hole feedback in our simulations. We find that the complex and turbulent nature of the SMUGGLE ISM leads to highly variable BH accretion. BH growth in SMUGGLE converges at gas mass resolutions $\lesssim3\times10^3{\rm M_\odot}$. We show that the low resolution simulations combined with the super-Lagrangian refinement scheme are able to produce central gas dynamics and BH accretion rates very similar to that of the uniform high resolution simulations. We further explore BH fueling by simulating galaxy mergers. The interaction between the galaxies causes an inflow of gas towards the galactic centres and results in elevated and bursty star formation. The peak gas densities near the BHs increase by orders of magnitude resulting in enhanced accretion. Our results support the idea that galaxy mergers can trigger AGN activity, although the instantaneous accretion rate depends strongly on the local ISM. We also show that the level of merger-induced enhancement of BH fueling predicted by the SMUGGLE model is much smaller compared to the predictions by simulations using an effective equation of state model of the ISM., Comment: 16 pages, 10 figures

We present a suite of high resolution hydrodynamic simulations of binaries immersed in circumbinary accretion disks (CBDs). For the first time, we investigate the preferential accretion rate as a function of both eccentricity $e_{\rm b}$ and mass ratio $q_{\rm b}$ in a densely sampled parameter space, finding that when compared with circular binaries, mass ratios grow more efficiently in binaries on moderately eccentric orbits ($0.0 \lesssim e_{\rm b} \lesssim 0.4$), and high eccentricities ($e_{\rm b} \gtrsim 0.6 $) suppress mass ratio growth. We suggest that this non-monotonic preferential accretion behaviour may produce an observable shift in the mass ratio distributions of stellar binaries and massive black hole binaries. We further find that the response of a CBD can be divided into three regimes, depending on eccentricity and mass ratio: (i) CBDs around circular binaries always precess freely, whereas CBDs around eccentric binaries either (ii) undergo forced precession or (iii) remain locked at an angle with respect to the binary periapsis. Forced precession in eccentric binaries is associated with strong modulation of individual accretion rates on the precession timescale, a potentially observable signature in accreting binaries with short orbital periods. We provide CBD locking angles and precession rates as a function of $e_{\rm b}$ and $q_{\rm b}$ for our simulation suite., Comment: 15 pages, 14 figures. Published in Monthly Notices of the Royal Astronomical Society

Observations have shown that the star-formation activity and the morphology of galaxies are closely related, but the underlying physical connection is not well understood. Using the TNG50 simulation, we explore the quenching and the morphological evolution of the 102 massive quiescent galaxies in the mass range of $10.5<\log(M_{\rm stellar}/M_{\odot})<11.5$ selected at $z=0$. The morphology of galaxies is quantified based on their kinematics, and we measure the quenching timescale of individual galaxies directly from star formation history. We show that galaxies tend to be quenched more rapidly if they: (i) are satellites in massive halos, (ii) have lower star-forming gas fractions, or (iii) inject a larger amount of black hole kinetic feedback energy. By following the global evolutionary pathways, we conclude that quiescent discs are mainly disc galaxies that are recently and slowly quenched. Approximately half of the quiescent ellipticals at $z=0$ are rapidly quenched at higher redshifts while still disc-like. While being quiescent, they gradually become more elliptical mostly by disc heating, yet these ellipticals still retain some degree of rotation. The other half of quiescent ellipticals with the most random motion-dominated kinematics build up large spheroidal components before quenching primarily by mergers, or in some cases, misaligned gas accretion. However, the mergers that contribute to morphological transformation do not immediately quench galaxies in many cases. In summary, we find that quenching and morphological transformation are decoupled. We conclude that the TNG black hole feedback -- in combination with the stochastic merger history of galaxies -- leads to a large diversity of quenching timescales and a rich morphological landscape., Comment: Submitted to MNRAS. 9 Figures 17 Pages. Comments are very welcome!

Radio relics are arc-like synchrotron sources at the periphery of galaxy clusters, produced by cosmic-ray electrons in a $\mu$G magnetic field which are believed to have been (re-)accelerated by merger shock fronts. However, not all relics appear at the same location as shocks as seen in the X-ray. In a previous work, we suggested that the shape of some relics may result from the pre-existing spatial distribution of cosmic-ray electrons, and tested this hypothesis using simulations by launching AGN jets into a cluster atmosphere with sloshing gas motions generated by a previous merger event. We showed that these motions could transport the cosmic ray-enriched material of the AGN bubbles to large radii and stretch it in a tangential direction, producing a filamentary shape resembling a radio relic. In this work, we improve our physical description for the cosmic rays by modeling them as a separate fluid which undergoes diffusion and Alfv\'en losses. We find that including this additional cosmic ray physics significantly diminishes the appearance of these filamentary features, showing that our original hypothesis is sensitive to the modeling of cosmic ray physics in the intracluster medium., Comment: 9 pages, 4 figures, accepted by the journal Galaxies for the Special Issue "A New Window on the Radio Emission from Galaxies, Galaxy Clusters and Cosmic Web: Current Status and Perspectives"

In theoretical models of galaxy evolution, AGN and star formation (SF) activity are closely linked and AGN feedback is routinely invoked to regulate galaxy growth. In order to constrain such models, we compare the hydrodynamical simulations IllustrisTNG and SIMBA, and the semi-analytical model SAG to the empirical results on AGN and SF at cosmic noon ($0.75 < z < 2.25$) reported in Florez et al. (2020). The empirical results are based on a large mass-complete sample drawn from 93,307 galaxies with and without high X-ray luminosity AGN ($L_X \gtrsim 10^{44}$ erg s$^{-1}$), selected from a 11.8 deg$^2$ area ($\sim 0.18$ Gpc$^3$ comoving volume at $z=0.75-2.25$). The main results of our comparisons are: (i) SAG and IllustrisTNG both qualitatively reproduce the empirical result that galaxies with high X-ray luminosity AGN have higher mean SFR, at a given stellar mass, than galaxies without such AGN. SAG, however, strongly over-produces the number density of high X-ray luminosity AGN by a factor of 10 to 100, while IllustrisTNG shows a lack of high X-ray luminosity AGN at high stellar mass ($M* > 10^{11} \ M_{\odot}$) at $z \sim 2$. (ii) In SIMBA, the mean SFR of galaxies with high X-ray luminosity AGN is lower than the SFR of galaxies without such AGN. Contrary to the data, many high X-ray luminosity AGN in SIMBA have quenched SF, suggesting that AGN feedback, or other feedback modes in galaxies with such AGN, might be too efficient in SIMBA., Comment: 20 pages, 7 figures. Accepted for publication in MNRAS

Direct collapse black holes~(BH) are promising candidates for producing massive $z\gtrsim 6$ quasars, but their formation requires fine-tuned conditions. In this work, we use cosmological zoom simulations to study systematically the impact of requiring: 1) low gas angular momentum, and 2) a minimum incident Lyman-Werner~(LW) flux in order to form BH seeds. We probe the formation of seeds (with initial masses of $M_{\rm seed} \sim 10^4$ - $10^6 M_{\odot}/h)$ in halos with a total mass $> 3000\times M_{\mathrm{seed}}$ and a dense, metal poor gas mass $> 5\times M_{\mathrm{seed}}$. We find that the seed-forming halos have a prior history of star formation and metal enrichment, but contain pockets of dense, metal poor gas. When seeding is further restricted to halos with low gas spins, the number of seeds formed is suppressed by factors of $\sim6$ compared to the baseline model, regardless of the seed mass. Seed formation is much more strongly impacted if the dense, metal poor gas is required to have a critical LW flux ($J_{\mathrm{crit}}$). Even for $J_{\mathrm{crit}}$ values as low as $50J_{21}$, no $8\times10^{5}M_{\odot}/h$ seeds are formed. While lower mass ($1.25\times10^{4},1\times10^{5} M_{\odot}/h$) seeds do form, they are strongly suppressed~(by factors of $\sim10-100$) compared to the baseline model at gas mass resolutions of $\sim10^4~M_{\odot}/h$ (with even stronger suppression at higher resolutions). As a result, BH merger rates are also similarly suppressed. Since early BH growth is dominated by mergers in our models, no seeds are able to grow to the supermassive regime~($\gtrsim10^6 M_{\odot}/h$) by $z=7$. Our results hint that producing the bulk of the $z\gtrsim6$ supermassive BH population may require alternate seeding scenarios that do not depend on the LW flux, early BH growth dominated by rapid or super-Eddington accretion, or a combination of these possibilities., Comment: 21 pages, 13 figures

The TNG50 cosmological simulation produces X-ray emitting bubbles, shells, and cavities in the circumgalactic gas above and below the stellar disks of Milky Way- and Andromeda-like galaxies with morphological features reminiscent of the eROSITA and Fermi bubbles in the Galaxy. Two-thirds of the 198 MW/M31 analogues inspected in TNG50 at z=0 show one or more large-scale, coherent features of over-pressurized gas that impinge into the gaseous halo. Some of the galaxies include a succession of bubbles or shells of increasing size, ranging from a few to many tens of kpc. These are prominent in gas pressure, X-ray emission and gas temperature, and often exhibit sharp boundaries with typical shock Mach numbers of 2-4. The gas in the bubbles outflows with maximum (95th pctl) radial velocities of 100-1500 km/s. TNG50 bubbles expand with speeds as high as 1000-2000 km/s (about 1-2 kpc/Myr), but with a great diversity and with larger bubbles expanding at slower speeds. The bubble gas is at 10^6.4-7.2 K temperatures and is enriched to metallicities of 0.5-2 solar. In TNG50, the bubbles are a manifestation of episodic, kinetic, wind-like energy injections from the supermassive black holes at the galaxy centers that accrete at low Eddington ratios. According to TNG50, X-ray, and possibly gamma-ray, bubbles similar to those observed in the Milky Way should be a frequent feature of disk-like galaxies prior to, or on the verge of, being quenched. They should be within the grasp of eROSITA in the local Universe., Comment: Accepted on MNRAS. Added details on the SMBH feedback model and a new panel in Fig. 11 with the X-ray luminosities of TNG50 SMBHs. Updated discussion and observability opportunities

Deciphering the formation of supermassive black holes~(SMBHs) is a key science goal for upcoming observational facilities. In most theoretical channels proposed so far, the seed formation depends crucially on local gas conditions. We systematically characterize the impact of a range of gas based black hole seeding prescriptions on SMBH populations using cosmological simulations. Seeds of mass $M_{\mathrm{seed}}\sim 10^3-10^{6}~M_{\odot}/h$ are placed in halos that exceed critical thresholds for star-forming, metal-poor gas mass and halo mass (defined as $\tilde{M}_{\mathrm{sf,mp}}$ and $\tilde{M}_{\mathrm{h}}$, respectively, in units of $M_{\mathrm{seed}}$). We quantify the impact of these parameters on the properties of $z\geq7$ SMBHs. Lower seed masses produce much higher BH merger rates (by factors of $\sim10$ and $\sim1000$ at $z\sim7$ and $z\sim15$, respectively). For fixed seed mass, we find that $\tilde{M}_{\mathrm{h}}$ has the strongest impact on the BH population at high redshift ($z\gtrsim15$, where a factor of 10 increase in $\tilde{M}_{\mathrm{h}}$ suppresses merger rates by $\gtrsim 100$). At lower redshift ($z\lesssim15$), we find that $\tilde{M}_{\mathrm{sf,mp}}$ has a larger impact on the BH population. Increasing $\tilde{M}_{\mathrm{sf,mp}}$ from $5-150$ suppresses the merger rates by factors of $\sim8$ at $z\sim7-15$. This suggests that the seeding criteria explored here could leave distinct imprints on the redshift distribution of LISA merger rates. In contrast, AGN luminosity functions are much less sensitive to seeding criteria, varying by factors $\lesssim2-3$ within the seed parameters we have explored. Such variations will be challenging to probe even with future sensitive instruments such as Lynx or JWST. Overall, our systematic parameter study provides a useful benchmark for development of seed models for large-volume cosmological simulations., Comment: 25 pages, 23 figures

Using the IllustrisTNG cosmological galaxy formation simulations, we analyze the physical properties of young quiescent galaxies at z=2 with stellar masses above 10^10.5 solar masses. This key population provides an unaltered probe into the evolution of galaxies from star-forming to quiescent and has been recently targeted by several observational studies. Young quiescent galaxies in the simulations do not appear unusually compact, in tension with observations, but they show unique age gradients that are qualitatively consistent with the observed color gradients. In particular, more than half of the simulated young quiescent galaxies show positive age profiles due to recent intense central starbursts, which are triggered by significant mergers. Yet, there is a sizable population of recently quenched galaxies without significant mergers and with flat age profiles. Our results suggest that mergers play a fundamental role in structural transformation, but are not the only available pathway to quench a z=2 galaxy., Comment: 10 pages, 5 figures, code publicly available at: https://github.com/pathakde/Pathak_2021 (DOI: 10.5281/zenodo.5093727)

Several lines of evidence suggest the Milky Way underwent a major merger at z~2 with a galaxy known as Gaia-Sausage-Enceladus (GSE). Here we use H3 Survey data to argue that GSE entered the Galaxy on a retrograde orbit based on a population of highly retrograde stars with chemistry similar to the largely radial GSE debris. We present the first tailored, high-resolution N-body simulations of the merger. From a grid of ~500 simulations we find a GSE with $M_{*}=5\times10^{8}\ M_{\odot}, M_{\rm{DM}}=2\times10^{11} M_{\odot}$ (a 2.5:1 total mass merger) best matches the H3 data. This simulation shows the retrograde GSE stars are stripped from its outer disk early in the merger before the orbit loses significant angular momentum. Despite being selected purely on angular momenta and radial distributions, this simulation reproduces and explains the following empirical phenomena: (i) the elongated, triaxial shape of the inner halo (axis ratios $10:7.9:4.5$), whose major axis is at ~35{\deg} to the plane and connects GSE's apocenters, (ii) the Hercules-Aquila Cloud & the Virgo Overdensity, which arise due to apocenter pile-up, (iii) the 2 Gyr lag between the quenching of GSE and the truncation of the age distribution of the in-situ halo, which tracks the 2 Gyr gap between the first and final GSE pericenters. We make the following predictions: (i) the inner halo has a "double-break" density profile with breaks at both ~15-18 kpc and 30 kpc, coincident with the GSE apocenters, (ii) the outer halo has retrograde streams containing ~10% of GSE stars awaiting discovery at >30 kpc. The retrograde (radial) GSE debris originates from its outer (inner) disk -- exploiting this trend we reconstruct the stellar metallicity gradient of GSE ($-0.04\pm0.01$ dex $r_{\rm{50}}^{-1}$). These simulations imply GSE delivered ~20% of the Milky Way's present-day dark matter and ~50% of its stellar halo. (ABRIDGED), Comment: Submitted to ApJ. See https://rohannaidu.github.io/moviesdata/ for merger movies. The simulation data is publicly available at https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/UFVSTH . Comments greatly appreciated and very welcome! v2 fixes typos and adds references

We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final instalment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as disky galaxies with stellar masses of Mstar = 10^10.5-11.2 Msun in relative isolation at z = 0. By defining satellites as galaxies with Mstar > 5*10^6 Msun within 300 kpc (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median (16th - 84th percentiles) TNG50 MW/M31-like galaxy hosts a total of 5 (2-11) satellites with Mstar > 5*10^6 Msun, reaching up to Mstar ~ 10^8.5 Msun (10^7.4-9.4 Msun). The abundance of subhaloes with Mdyn > 5*10^7 Msun is larger by a factor of more than 10. The number of all satellites (subhaloes) ever accreted is larger by a factor of 4-5 (3-5) than those surviving to z = 0. Hosts with larger galaxy stellar mass, brighter K-band luminosity, larger total halo mass, and more recent halo assembly typically have a larger number of surviving satellites. The satellite abundances around TNG50 MW/M31-like galaxies are consistent with similar hosts from observational surveys (e.g. SAGA) and previous simulations (e.g. Latte). While the observed MW satellite system falls within the TNG50 scatter across all stellar masses considered, M31 is slightly more satellite-rich than our 1 sigma scatter, possibly due to volume and mass limitations. We find a handful of systems with both a Large and a Small Magellanic Cloud-like satellite. There is no missing satellites problem with TNG50., Comment: Accepted by MNRAS. TNG50 is publicly available at https://www.tng-project.org/

We compare the star forming main sequence (SFMS) -- both integrated and resolved on 1kpc scales -- between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z~1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2-1dex between observed and simulated main sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M_*>10^10Msun, even after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M_*>10^10.5Msun, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In TNG this inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates. In contrast, the original Illustris simulation, without this same physical SMBH mechanism, does not reproduce the central SFR profile suppression seen in data. The observed sSFR profiles provide support for the TNG quenching mechanism and how it affects gas on kiloparsec scales in the centers of galaxies., Comment: Main results in Figs 1 and 3. The TNG50 data is now fully publicly available at https://www.tng-project.org/

To break the degeneracy among galactic stellar components, we extract kinematic structures using the framework described in Du et al. (2019, 2020). For example, the concept of stellar halos is generalized to weakly-rotating structures that are composed of loosely bound stars, which can hence be associated to both disk and elliptical type morphologies. By applying this method to central galaxies with stellar mass $10^{10-11.5}\ M_\odot$ from the TNG50 simulation, we identify three broadly-defined types of galaxies: ones dominated by disk, by bulge, or by stellar halo structures. We then use the simulation to infer the underlying connection between the growth of structures and physical processes over cosmic time. Tracing galaxies back in time, we recognize three fundamental regimes: an early phase of evolution ($z\gtrsim2$), and internal and external (mainly mergers) processes that act at later times. We find that disk- and bulge-dominated galaxies are not significantly affected by mergers since $z\sim2$; the difference in their present-day structures originates from two distinct evolutionary pathways, extended vs. compact, that are likely determined by their parent dark matter halos; i.e., nature. On the other hand, slow rotator elliptical galaxies are typically halo-dominated, forming by external processes (e.g. mergers) in the later phase, i.e., nurture. This picture challenges the general idea that elliptical galaxies are the same objects as classical bulges. In observations, both bulge- and halo-dominated galaxies are likely to be classified as early-type galaxies with compact morphology and quiescent star formation. However, here we find them to have very different evolutionary histories., Comment: 31 pages, 28 figures. Accepted for publication in ApJ

We investigate the morphology of the stellar distribution in a sample of Milky Way (MW) like galaxies in the TNG50 simulation. Using a local in shell iterative method (LSIM) as the main approach, we explicitly show evidence of twisting (in about 52% of halos) and stretching (in 48% of them) in the real space. This is matched with the re-orientation observed in the eigenvectors of the inertia tensor and gives us a clear picture of having a re-oriented stellar distribution. We make a comparison between the shape profile of dark matter (DM) halo and stellar distribution and quite remarkably see that their radial profiles are fairly close, especially at small galactocentric radii where the stellar disk is located. This implies that the DM halo is somewhat aligned with stars in response to the baryonic potential. The level of alignment mostly decreases away from the center. We study the impact of substructures in the orbital circularity parameter. It is demonstrated that in some cases, far away substructures are counter-rotating compared with the central stars and may flip the sign of total angular momentum and thus the orbital circularity parameter. Truncating them above 150 kpc, however, retains the disky structure of the galaxy as per initial selection. Including the impact of substructures in the shape of stars, we explicitly show that their contribution is subdominant. Overlaying our theoretical results to the observational constraints from previous literature, we establish fair agreement., Comment: 29 pages, 21 figures, Accepted for publication in ApJ

Radio relics in galaxy clusters are extended synchrotron sources produced by cosmic-ray electrons in the $\mu$G magnetic field. Many relics are found in the cluster periphery and have a cluster-centric, narrow arc-like shape, which suggests that the electrons are accelerated or re-accelerated by merger shock fronts propagating outward in the intracluster plasma. In the X-ray, some relics do exhibit such shocks at the location of the relic, but many do not. We explore the possibility that radio relics trace not the shock fronts but the shape of the underlying distribution of seed relativistic electrons, lit up by a recent shock passage. We use magnetohydrodynamic simulations of cluster mergers and include bubbles of relativistic electrons injected by jets from the central AGN or from an off-center radio galaxy. We show that the merger-driven gas motions (a) can advect the bubble cosmic rays to very large radii, and (b) spread the relativistic seed electrons preferentially in tangential direction -- along the gravitational equipotential surfaces -- producing extended, filamentary or sheet-like regions of intracluster plasma enriched with aged cosmic rays, which resemble radio relics. Once a shock front passes across such a region, the sharp radio emission edges would trace the sharp boundaries of these enriched regions rather than the front. We also show that these elongated cosmic ray features are naturally associated with magnetic fields stretched tangentially along their long axis, which could help explain the high polarization of relics., Comment: 18 pages, 13 figures, accepted by ApJ

The study of velocity fields of the hot gas in galaxy clusters can help to unravel details of microphysics on small-scales and to decipher the nature of feedback by active galactic nuclei (AGN). Likewise, magnetic fields as traced by Faraday rotation measurements (RMs) inform about their impact on gas dynamics as well as on cosmic ray production and transport. We investigate the inherent relationship between large-scale gas kinematics and magnetic fields through non-radiative magnetohydrodynamical simulations of the creation, evolution and disruption of AGN jet-inflated lobes in an isolated Perseus-like galaxy cluster, with and without pre-existing turbulence. In particular, we connect cluster velocity measurements with mock RM maps to highlight their underlying physical connection, which opens up the possibility of comparing turbulence levels in two different observables. For single jet outbursts, we find only a local impact on the velocity field, i.e. the associated increase in velocity dispersion is not volume-filling. Furthermore, in a setup with pre-existing turbulence, this increase in velocity dispersion is largely hidden. We use mock X-ray observations to show that at arcmin resolution, the velocity dispersion is therefore dominated by existing large-scale turbulence and is only minimally altered by the presence of a jet. For the velocity structure of central gas uplifted by buoyantly rising lobes, we find fast, coherent outflows with low velocity dispersion. Our results highlight that projected velocity distributions show complex structures which pose challenges for the interpretation of observations., Comment: 19 pages, 9 figures, submitted to MNRS. Comments welcome!

We present a comprehensive analysis of the shape of dark matter (DM) halos in a sample of 25 Milky Way-like galaxies in TNG50 simulation. Using an Enclosed Volume Iterative Method (EVIM), we infer an oblate-to-triaxial shape for the DM halo with the median $T \simeq 0.24 $. We group DM halos in 3 different categories. Simple halos (32% of population) establish principal axes whose ordering in magnitude does not change with radius and whose orientations are almost fixed throughout the halo. Twisted halos (32% of population), experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36% of population) demonstrate a stretching in their principal axes lengths where the ordering of different eigenvalues change with radius. Subsequently, the halo experiences a "rotation" of $\sim$90 deg where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of re-orienting ellipsoid in twisted and stretched halos. We examine the impact of baryonic physics on DM halo shape through a comparison to dark matter only (DMO) simulations. This suggests a triaxial (prolate) halo. We analyze the impact of substructure on DM halo shape in both hydro and DMO simulations and confirm that their impacts are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle of satellites' angular momentum with galaxy's angular momentum grows with radius. However, stretched halos show a flat distribution of angles. Overlaying our theoretical outcome on the observational results presented in the literature establishes a fair agreement., Comment: 32 pages, 28 plots, Accepted for publication in ApJ

Submillimetre galaxies (SMGs) have long posed a challenge for theorists, and self-consistently reproducing the properties of the SMG population in a large-volume cosmological hydrodynamical simulation has not yet been achieved. We use a scaling relation derived from previous simulations plus radiative transfer calculations to predict the submm flux densities of simulated SMGs drawn from cosmological simulations from the Illustris and IllustrisTNG projects based on the simulated galaxies' star formation rates (SFRs) and dust masses and compare the predicted number counts with observations. We find that the predicted SMG number counts based on IllustrisTNG are significantly less than observed (more than 1 dex at $S_{850} \gtrsim 4$ mJy). The simulation from the original Illustris project yields more SMGs than IllustrisTNG: the predicted counts are consistent with those observed at both $S_{850} \lesssim 5$ mJy and $S_{850} \gtrsim 9$ mJy and only a factor of $\sim 2$ lower than observed at intermediate flux densities. The redshift distribution of SMGs with $S_{850} > 3$ mJy in IllustrisTNG is consistent with the observed distribution, whereas the Illustris redshift distribution peaks at significantly lower redshift (1.5 vs. 2.8). We demonstrate that IllustrisTNG hosts fewer SMGs than Illustris because in the former, high-mass ($M_{\star} \sim 10^{11} \, \text{M}_{\odot}$) $z \sim 2-3$ galaxies have lower dust masses and SFRs than in Illustris owing to differences in the sub-grid models for stellar or/and active galactic nucleus (AGN) feedback between the two simulations (we unfortunately cannot isolate the specific cause(s) post hoc). Our results demonstrate that because our method enables predicting SMG number counts in post-processing with a negligible computational expense, SMGs can provide useful constraints for tuning sub-grid models in future large-volume cosmological simulations., Comment: MNRAS, in press; typo corrected

We use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to explore the properties and origin of cold circumgalactic medium (CGM) gas around massive galaxies (M* > 10^11 Msun) at intermediate redshift (z~0.5). We discover a significant abundance of small-scale, cold gas structure in the CGM of 'red and dead' elliptical systems, as traced by neutral HI and MgII. Halos can host tens of thousands of discrete absorbing cloudlets, with sizes of order a kpc or smaller. With a Lagrangian tracer analysis, we show that cold clouds form due to strong drho/rho >> 1 gas density perturbations which stimulate thermal instability. These local overdensities trigger rapid cooling from the hot virialized background medium at ~10^7 K to radiatively inefficient ~10^4 K clouds, which act as cosmologically long-lived, 'stimulated cooling' seeds in a regime where the global halo does not satisfy the classic tcool/tff < 10 criterion. Furthermore, these small clouds are dominated by magnetic rather than thermal pressure, with plasma beta << 1, suggesting that magnetic fields may play an important role. The number and total mass of cold clouds both increase with resolution, and the ~8x10^4 Msun cell mass of TNG50 enables the ~few hundred pc, small-scale CGM structure we observe to form. Finally, we make a preliminary comparison against observations from the COS-LRG, LRG-RDR, COS-Halos, and SDSS LRG surveys. We broadly find that our recent, high-resolution cosmological simulations produce sufficiently high covering fractions of extended, cold gas as observed to surround massive galaxies., Comment: MNRAS

Supermassive black holes (SMBHs) which reside at the centres of galaxies can inject vast amounts of energy into the surrounding gas and are thought to be a viable mechanism to quench star-formation in massive galaxies. Here we study the $10^{9\textrm{--}12.5}\,\mathrm{M_\odot}$ stellar mass central galaxy population of the IllustrisTNG simulation, specifically the TNG100 and TNG300 volumes at \zeq{0}, and show how the three components -- SMBH, galaxy, and circumgalactic medium (CGM) -- are interconnected in their evolution. We find that gas entropy is a sensitive diagnostic of feedback injection. In particular, we demonstrate how the onset of the low-accretion BH feedback mode, realised in the IllustrisTNG model as a kinetic, BH-driven wind, leads not only to star-formation quenching at stellar masses $\gtrsim10^{10.5}\mathrm{M_\odot}$ but also to a change in thermodynamic properties of the (\emph{non}-star-forming) gas, both within the galaxy and beyond. The IllustrisTNG kinetic feedback from SMBHs increases the average gas entropy, within the galaxy and in the CGM, lengthening typical gas cooling times from $10\textrm{--}100\,\mathrm{Myr}$ to $1\textrm{--}10\,\mathrm{Gyr}$, effectively ceasing ongoing star-formation and inhibiting radiative cooling and future gas accretion. In practice, the same AGN feedback channel is simultaneously `ejective' and `preventative' and leaves an imprint on the temperature, density, entropy, and cooling times also in the outer reaches of the gas halo, up to distances of several hundred kiloparsecs. In the IllustrisTNG model, a long-lasting quenching state can occur for a heterogeneous CGM, whereby the hot and dilute CGM gas of quiescent galaxies contains regions of low-entropy gas with short cooling times., Comment: Accepted to MNRAS. Comments welcome

Hot gaseous atmospheres that permeate galaxies and extend far beyond their stellar distribution, where they are commonly referred to as the circumgalactic medium (CGM), imprint important information about feedback processes powered by the stellar populations of galaxies and their central supermassive black holes (SMBH). In this work we study the properties of this hot X-ray emitting medium using the IllustrisTNG cosmological simulations. We analyse their mock X-ray spectra, obtained from the diffuse and metal-enriched gas in TNG100 and TNG50, and compare the results with X-ray observations of nearby early-type galaxies. The simulations reproduce the observed X-ray luminosities ($L_{\rm X}$) and temperature ($T_{\rm X})$ at small ($

We study black hole - host galaxy correlations, and the relation between the over-massiveness (the distance from the average $M_{BH}-\sigma$ relation) of super-massive black holes (SMBHs) and star formation histories of their host galaxies in the Illustris and TNG100 simulations. We find that both simulations are able to produce black hole scaling relations in general agreement with observations at $z=0$, but with noticeable discrepancies. Both simulations show an offset from the observations for the $M_{BH}-\sigma$ relation, and the relation between $M_{BH}$ and the Sersic index. The relation between $M_{BH}$ and stellar mass $M_*$ is tighter than the observations, especially for TNG100. For massive galaxies in both simulations, the hosts of over-massive SMBHs (those above the mean $M_{BH}-\sigma$ relation) tend to have larger Sersic indices and lower baryon conversion efficiency, suggesting a multidimensional link between SMBHs and properties of their hosts. In Illustris, the hosts of over-massive SMBHs have formed earlier and have lower present-day star formation rates, in qualitative agreement with the observations for massive galaxies with $\sigma>100 \rm km/s$. For low-mass galaxies, such a correlation still holds in Illustris but does not exist in the observed data. For TNG100, the correlation between SMBH over-massiveness and star formation history is much weaker. The hosts of over-massive SMBHs generally have consistently larger star formation rates throughout history. These galaxies have higher stellar mass as well, due to the strong $M_{BH}-M_*$ correlation. Our findings show that simulated SMBH scaling relations and correlations are sensitive to features in the modeling of SMBHs., Comment: 18 pages, 11 figures, submitted to ApJ

We introduce the public version of the cosmological magnetohydrodynamical moving-mesh simulation code Arepo. This version contains a finite-volume magnetohydrodynamics algorithm on an unstructured, dynamic Voronoi tessellation coupled to a tree-particle-mesh algorithm for the Poisson equation either on a Newtonian or cosmologically expanding spacetime. Time-integration is performed adopting local timestep constraints for each cell individually, solving the fluxes only across active interfaces, and calculating gravitational forces only between active particles, using an operator-splitting approach. This allows simulations with high dynamic range to be performed efficiently. Arepo is a massively distributed-memory parallel code, using the Message Passing Interface (MPI) communication standard and employing a dynamical work-load and memory balancing scheme to allow optimal use of multi-node parallel computers. The employed parallelization algorithms of Arepo are deterministic and produce binary-identical results when re-run on the same machine and with the same number of MPI ranks. A simple primordial cooling and star formation model is included as an example of sub-resolution models commonly used in simulations of galaxy formation. Arepo also contains a suite of computationally inexpensive test problems, ranging from idealized tests for automated code verification to scaled-down versions of cosmological galaxy formation simulations, and is extensively documented in order to assist adoption of the code by new scientific users., Comment: 39 pages, 15 figures, accepted in ApJS, https://www.arepo-code.org, repository: https://gitlab.mpcdf.mpg.de/vrs/arepo

Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations between the specific star formation rate (sSFR), stellar mass (M$_{\rm{star}}$), and black hole mass (M$_{\rm{BH}}$) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and ten model variations that alter the parameters of the black hole model. Focusing on central galaxies at $z = 0$ with M$_{\rm{star}} > 10^{10}$ M$_{\odot}$, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular M$_{\rm{BH}}$ threshold above which galaxies are found to sharply transition from being mostly star-forming to mostly quiescent. As a result of this behavior, the fraction of quiescent galaxies as a function of M$_{\rm{star}}$ is sensitive to both the normalization of the M$_{\rm{BH}}$-M$_{\rm{star}}$ relation and the M$_{\rm{BH}}$ threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M$_{\rm{BH}}$ measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in M$_{\rm{BH}}$ at a given M$_{\rm{star}}$ and show a smoother decline in sSFR with M$_{\rm{BH}}$., Comment: 20 pages, submitted to MNRAS

Motivated by the recently discovered kinematic "Hubble sequence" shown by the stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a comparable galaxy sample at z = 0 with a stellar mass range from 5E9 to 5E11 solar masses, selected from the IllustrisTNG simulation and study their stellar orbit compositions in relation to a number of other fundamental galaxy properties.We find that the TNG100 simulation broadly reproduces the observed fractions of different orbital components and their stellar mass dependencies. In particular, the mean mass dependencies of the luminosity fractions for the kinematically warm and hot orbits are well reproduced within model uncertainties of the observed galaxies. The simulation also largely reproduces the observed peak and trough features at a stellar mass of 1-2E10 solar masses, in the mean distributions of the cold- and hot-orbit fractions, respectively, indicating fewer cooler orbits and more hotter orbits in both more- and less-massive galaxies beyond such a mass range. Several marginal disagreements are seen between the simulation and observations: the average cold-orbit (counter-rotating) fractions of the simulated galaxies below (above) a stellar mass of 6E10 solar masses, are systematically higher than the observational data by < 10% (absolute orbital fraction); the simulation also seems to produce more scatter for the cold-orbit fraction and less so for the non-cold orbits at any given galaxy mass. Possible causes that stem from the adopted heating mechanisms are discussed., Comment: 12 pages, 6 figures, 3 tables, submitted to MNRAS. Comments are welcome!

The James Webb Space Telescop (JWST) promises to revolutionise our understanding of the early Universe, and contrasting its upcoming observations with predictions of the $\Lambda$CDM model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multi-band galaxy luminosity functions from $z=2$ to $z=10$. We put particular emphasis on the exploration of different dust attenuation models to determine galaxy luminosity functions for the rest-frame ultraviolet (UV), and apparent wide NIRCam bands. Our most detailed dust model is based on continuum Monte Carlo radiative transfer calculations employing observationally calibrated dust properties. This calibration results in constraints on the redshift evolution of the dust attenuation normalisation and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalisation compared to most previous theoretical studies. Overall we find good agreement between the rest-frame UV luminosity functions and observational data for all redshifts, also beyond the regimes used for the dust-model calibrations. Furthermore, we also recover the observed high redshift ($z=4-6$) UV luminosity versus stellar mass relation, the H$\alpha$ versus star formation rate relation, and the H$\alpha$ luminosity function at $z=2$. The bright end ($M_{\rm UV}>-19.5$) cumulative galaxy number densities are consistent with observational data. For the F200W NIRCam band, we predict that JWST will detect $\sim 80$ ($\sim 200$) galaxies with a signal-to-noise ratio of $10$ ($\sim 5$) within the NIRCam field of view, $2.2\times2.2 \,{\rm arcmin}^{2}$, for a total exposure time of $10^5{\rm s}$ in the redshift range $z=8 \pm 0.5$. These numbers drop to $\sim 10$ ($\sim 40$) for an exposure time of $10^4{\rm s}$., Comment: 36 pages, 24 figures, MNRAS submitted

The majority of baryons reside beyond the optical extent of a galaxy in the circumgalactic and intergalactic media (CGM/IGM). Gaseous halos are inextricably linked to the appearance of their host galaxies through a complex story of accretion, feedback, and continual recycling. The energetic processes, which define the state of gas in the CGM, are the same ones that 1) regulate stellar growth so that it is not over-efficient, and 2) create the diversity of today's galaxy colors, SFRs, and morphologies spanning Hubble's Tuning Fork Diagram. They work in concert to set the speed of growth on the star-forming Main Sequence, transform a galaxy across the Green Valley, and maintain a galaxy's quenched appearance on the Red Sequence. Most baryons in halos more massive than 10^12 Msolar along with their high-energy physics and dynamics remain invisible because that gas is heated above the UV ionization states. We argue that information on many of the essential drivers of galaxy evolution is primarily contained in this "missing" hot gas phase. Completing the picture of galaxy formation requires uncovering the physical mechanisms behind stellar and SMBH feedback driving mass, metals, and energy into the CGM. By opening galactic hot halos to new wavebands, we not only obtain fossil imprints of >13 Gyrs of evolution, but observe on-going hot-mode accretion, the deposition of superwind outflows into the CGM, and the re-arrangement of baryons by SMBH feedback. A description of the flows of mass, metals, and energy will only be complete by observing the thermodynamic states, chemical compositions, structure, and dynamics of T>=10^6 K halos. These measurements are uniquely possible with a next-generation X-ray observatory if it provides the sensitivity to detect faint CGM emission, spectroscopic power to measure absorption lines and gas motions, and high spatial resolution to resolve structures., Comment: White paper submitted to the Astro2020 Decadal Survey (5 pages, 2 figures)

We present a new cosmological, magnetohydrodynamical simulation for galaxy formation: TNG50, the third and final installment of the IllustrisTNG project. TNG50 evolves 2x2160^3 dark-matter particles and gas cells in a volume 50 comoving Mpc across. It hence reaches a numerical resolution typical of zoom-in simulations, with a baryonic element mass of 8.5x10^4 Msun and an average cell size of 70-140 parsecs in the star-forming regions of galaxies. Simultaneously, TNG50 samples ~700 (6,500) galaxies with stellar masses above 10^10 (10^8) Msun at z=1. Here we investigate the structural and kinematical evolution of star-forming galaxies across cosmic time (0 < z < 6). We quantify their sizes, disk heights, 3D shapes, and degree of rotational vs. dispersion-supported motions as traced by rest-frame V-band light (i.e. roughly stellar mass) and by Halpha light (i.e. star-forming and dense gas). The unprecedented resolution of TNG50 enables us to model galaxies with sub-kpc half-light radii and with <300-pc disk heights. Coupled with the large-volume statistics, we characterize a diverse, redshift- and mass-dependent structural and kinematical morphological mix of galaxies all the way to early epochs. Our model predicts that for star-forming galaxies the fraction of disk-like morphologies, based on 3D stellar shapes, increases with both cosmic time and galaxy stellar mass. Gas kinematics reveal that the vast majority of 10^9-11.5 Msun star-forming galaxies are rotationally-supported disks for most cosmic epochs (Vmax/sigma>2-3, z<5), being dynamically hotter at earlier epochs (z>1.5). Despite large velocity dispersion at high redshift, cold and dense gas in galaxies predominantly arranges in disky or elongated shapes at all times and masses; these gaseous components exhibit rotationally-dominated motions far exceeding the collisionless stellar bodies., Comment: MNRAS. Highlights: Figures 9, 14, 15. See companion paper by Nelson et al. 2019b. Visuals at http://www.tng-project.org

We present the new TNG50 cosmological, magnetohydrodynamical simulation -- the third and final volume of the IllustrisTNG project. This simulation occupies a unique combination of large volume and high resolution, with a 50 Mpc box sampled by 2160^3 gas cells (baryon mass of 8x10^4 Msun). The median spatial resolution of star-forming ISM gas is ~100-140 parsecs. This resolution approaches or exceeds that of modern 'zoom' simulations of individual massive galaxies, while the volume contains ~20,000 resolved galaxies with M*>10^7 Msun. Herein we show first results from TNG50, focusing on galactic outflows driven by supernovae as well as supermassive black hole feedback. We find that the outflow mass loading is a non-monotonic function of galaxy stellar mass, turning over and rising rapidly above 10^10.5 Msun due to the action of the central black hole. Outflow velocity increases with stellar mass, and at fixed mass is faster at higher redshift. The TNG model can produce high velocity, multi-phase outflows which include cool, dense components. These outflows reach speeds in excess of 3000 km/s out to 20 kpc with an ejective, BH-driven origin. Critically, we show how the relative simplicity of model inputs (and scalings) at the injection scale produces complex behavior at galactic and halo scales. For example, despite isotropic wind launching, outflows exhibit natural collimation and an emergent bipolarity. Furthermore, galaxies above the star-forming main sequence drive faster outflows, although this correlation inverts at high mass with the onset of quenching, whereby low luminosity, slowly accreting, massive black holes drive the strongest outflows., Comment: MNRAS, see also companion paper by Pillepich et al. (2019b). Visualizations, movies, and an image gallery of paper figures available on the TNG50 website: www.tng-project.org