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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. [ABSTRACT FROM AUTHOR]

While the first "seeds" of supermassive black holes (BH) can range from |$\sim 10^2-10^6 \rm ~{\rm M}_{\odot }$|⁠ , the lowest mass seeds (⁠|$\lesssim 10^3~\rm {\rm M}_{\odot }$|⁠) are inaccessible to most cosmological simulations due to resolution limitations. We present our new BRAHMA simulations that use a novel flexible seeding approach to predict the |$z\ge 7$| BH populations for low-mass seeds. We ran two types of boxes that model |$\sim 10^3~\rm {\rm M}_{\odot }$| 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 |$\sim 10^3~\rm {\rm M}_{\odot }$| seeds and place them within haloes with dense, metal-poor gas. Second, we have lower resolution, larger volume |$[18~\mathrm{Mpc}]^3$| (BRAHMA-18-E4), and |$\sim [36~\mathrm{Mpc}]^3$| (BRAHMA-36-E5) boxes that seed their smallest resolvable |$\sim 10^4~\&~10^5~\mathrm{{\rm M}_{\odot }}$| BH descendants using new stochastic seeding prescriptions calibrated using BRAHMA-9-D3. The three boxes together probe key BH observables between |$\sim 10^3\,\mathrm{ and}\,10^7~\rm {\rm M}_{\odot }$|⁠. The active galactic nuclei (AGN) luminosity function variations are small (factors of |$\sim 2-3$|⁠) at the anticipated detection limits of potential future X-ray facilities (⁠|$\sim 10^{43}~ \mathrm{ergs~s^{-1}}$| at |$z\sim 7$|⁠). Our simulations predict BHs |$\sim 10-100$| times heavier than the local |$M_*$| versus |$M_{\mathrm{ bh}}$| relations, consistent with several JWST -detected AGN. For different seed models, our simulations merge binaries at |$\sim 1-15~\mathrm{kpc}$|⁠ , with rates of |$\sim 200-2000$| yr−1 for |$\gtrsim 10^3~\rm {\rm M}_{\odot }$| BHs, |$\sim 6-60$| yr−1 for |$\gtrsim 10^4~\rm {\rm M}_{\odot }$| BHs, and up to |$\sim 10$| yr−1 amongst |$\gtrsim 10^5~\rm {\rm M}_{\odot }$| BHs. These results suggest that Laser Interferometer Space Antenna mission has promising prospects for constraining seed models. [ABSTRACT FROM AUTHOR]

The physical origin of the seeds of supermassive black holes (SMBHs), with postulated initial masses ranging from ∼105 M⊙ to as low as ∼102 M⊙, is currently unknown. Most existing cosmological hydrodynamic simulations adopt very simple, ad hoc prescriptions for BH seeding and seed at unphysically high masses ∼105–106 M⊙. In this work, we introduce a novel sub-grid BH seeding model for cosmological simulations that is directly calibrated to high-resolution zoom simulations that explicitly resolve ∼103 M⊙ seeds forming within haloes with pristine, dense gas. We trace the BH growth along galaxy merger trees until their descendants reach masses of ∼104 or 105 M⊙. 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 combined influence of halo growth, dense gas formation, and metal enrichment on the formation of ∼103 M⊙ seeds. The environment-based seeding criterion seeds the descendants in rich environments with higher numbers of neighbouring 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. [ABSTRACT FROM AUTHOR]

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  id absorption (beyond the stellar contribution) in 46 per cent of massive galaxies (log  M */M⊙ > 10), with similar incidence rates in star-forming and quenching systems. Half of the absorption profiles are blueshifted by at least 100 km s−1, providing unambiguous evidence for neutral gas outflows. Galaxies with strong Na id absorption are distinguished by enhanced emission line ratios consistent with AGN ionization. We conservatively measure mass outflow rates of 3–100 M⊙ 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] ≲ −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. [ABSTRACT FROM AUTHOR]

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 idealized non-cosmological simulations of a galaxy with a realistic circumgalactic medium (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 transition region between the interstellar medium (ISM) and the CGM, while also providing refinement at the base of the wind. Without 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 star formation rate of galaxies. In future work, we will demonstrate other aspects of the Arkenstone model. [ABSTRACT FROM AUTHOR]

We analyse the stellar abundances of massive galaxies (log  M */M⊙ > 10.5) at redshift, z  = 2, in the IllustrisTNG simulation with the goal of guiding the interpretation of current and future observations, particularly from JWST. We find that the effective size, R e, of galaxies strongly affects the abundance measurements: both [Mg/H] and [Fe/H] are anticorrelated with R e, while the relative abundance [Mg/Fe] slightly increases with R e. The α enhancement as tracked by [Mg/Fe] traces the formation time-scale 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. [ABSTRACT FROM AUTHOR]

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 stellar/M⊙) < 11.5 selected at z  = 0. We show that galaxies tend to be quenched more rapidly if they (i) are satellites in massive haloes, (ii) have lower star-forming gas fractions, or (iii) inject a larger amount of black hole kinetic feedback energy. Following 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 quiescent, these 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 largely 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 time-scales and a rich morphological landscape. [ABSTRACT FROM AUTHOR]

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 ≳ 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 ≲ 5 mJy and S 850 ≳ 9 mJy and only a factor of ∼2 lower than those 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 versus 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 ∼ 2–3 galaxies have lower dust masses and SFRs than in Illustris owing to differences in the subgrid models for stellar and/or active galactic nucleus 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 subgrid models in future large-volume cosmological simulations. [ABSTRACT FROM AUTHOR]

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 ⋆ > 1011 M⊙ ) at intermediate redshift (⁠|$z \sim 0.5$|⁠). We discover a significant abundance of small-scale, cold gas structure in the CGM of 'red and dead' elliptical systems, as traced by neutral H  i and Mg  ii. 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 |$\delta \rho / \bar{\rho } \gg 1$| gas density perturbations that stimulate thermal instability. These local overdensities trigger rapid cooling from the hot virialized background medium at ∼107 K to radiatively inefficient ∼104 K clouds, which act as cosmologically long-lived, 'stimulated cooling' seeds in a regime where the global halo does not satisfy the classic t cool/ t ff < 10 criterion. Furthermore, these small clouds are dominated by magnetic rather than thermal pressure, with plasma β ≪ 1, suggesting that magnetic fields may play an important role. The number and total mass of cold clouds both increase with resolution, and the m gas ≃ 8 × 104 M⊙ 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. [ABSTRACT FROM AUTHOR]

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 star), and black hole mass (M 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 10 model variations that alter the parameters of the black hole model. Focusing on central galaxies at z  = 0 with M star > 1010 M⊙, 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 BH threshold above which galaxies are found to sharply transition from being mostly star forming to mostly quiescent. As a result of this behaviour, the fraction of quiescent galaxies as a function of M star is sensitive to both the normalization of the M BH– M star relation and the M BH threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical M 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 BH at a given M star and show a smoother decline in sSFR with M BH. [ABSTRACT FROM AUTHOR]

The James Webb Space Telescope (JWST) promises to revolutionize our understanding of the early Universe, and contrasting its upcoming observations with predictions of the Λ cold dark matter model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multiband 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 normalization and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalization 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 α versus star formation rate relation, and the H α luminosity function at z  = 2. The bright end (M UV > −19.5) cumulative galaxy number densities are consistent with observational data. For the F 200 W NIRCam band, we predict that JWST will detect ∼80 (∼200) galaxies with a signal-to-noise ratio of 10 (5) within the NIRCam field of view, |$2.2\times 2.2 \, {\rm arcmin}^{2}$|⁠ , for a total exposure time of |$10^5\, {\rm s}$| in the redshift range z  = 8 ± 0.5. These numbers drop to ∼10 (∼40) for an exposure time of |$10^4\, {\rm s}$|⁠. [ABSTRACT FROM AUTHOR]

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 21603 gas cells (baryon mass of 8 × 104 M⊙). The median spatial resolution of star-forming interstellar medium gas is ∼100−140 pc. This resolution approaches or exceeds that of modern 'zoom' simulations of individual massive galaxies, while the volume contains ∼20 000 resolved galaxies with |$M_\star \gtrsim 10^7$|  M⊙. 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 1010.5 M⊙ due to the action of the central black hole (BH). The outflow velocity increases with stellar mass, and at fixed mass it is faster at higher redshift. The TNG model can produce high-velocity, multiphase outflows that include cool, dense components. These outflows reach speeds in excess of 3000 km s−1 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 behaviour 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 BHs drive the strongest outflows. [ABSTRACT FROM AUTHOR]

We present a new cosmological, magnetohydrodynamical simulation for galaxy formation: TNG50, the third and final instalment of the IllustrisTNG project. TNG50 evolves 2 × 21603 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 |$8.5\times 10^4\, {\rm M}_{\odot }$| and an average cell size of 70–140 pc in the star-forming regions of galaxies. Simultaneously, TNG50 samples ∼700 (6500) galaxies with stellar masses above |$10^{10} \, (10^8)\, {\rm M}_{\odot }$| 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, disc heights, 3D shapes, and degree of rotational versus dispersion-supported motions as traced by rest-frame V -band light (i.e. roughly stellar mass) and by |$\rm H\,\alpha$| 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 disc 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 disc-like morphologies, based on 3D stellar shapes, increases with both cosmic time and galaxy stellar mass. Gas kinematics reveal that the vast majority of |$10^{9-11.5}\, {\rm M}_{\odot }$| star-forming galaxies are rotationally supported discs for most cosmic epochs (V rot/σ > 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. [ABSTRACT FROM AUTHOR]

We select galaxies from the IllustrisTNG hydrodynamical simulations (⁠|$M_{\rm stars}\gt 10^9 \, {\rm M}_\odot$| at 0 ≤ z ≤ 2) and characterize the shapes and evolutions of their UVJ and star formation rate–stellar mass (SFR– M stars) diagrams. We quantify the systematic uncertainties related to different criteria to classify star-forming versus quiescent galaxies, different SFR estimates, and by accounting for the star formation measured within different physical apertures. The TNG model returns the observed features of the UVJ diagram at z ≤ 2, with a clear separation between two classes of galaxies. It also returns a tight star-forming main sequence (MS) for |$M_{\rm stars}\lt 10^{10.5} \, ({\rm M}_\odot)$| with a ∼0.3 dex scatter at z ∼ 0 in our fiducial choices. If a UVJ -based cut is adopted, the TNG MS exhibits a downwardly bending at stellar masses of about 1010.5−10.7 M⊙. Moreover, the model predicts that |${\sim }80\, (50)$|  per cent of 1010.5−11 M⊙ galaxies at z  = 0 (z  = 2) are quiescent and the numbers of quenched galaxies at intermediate redshifts and high masses are in better agreement with observational estimates than previous models. However, shorter SFR-averaging time-scales imply higher normalizations and scatter of the MS, while smaller apertures lead to underestimating the galaxy SFRs: overall we estimate the inspected systematic uncertainties to sum up to about 0.2−0.3 dex in the locus of the MS and to about 15 percentage points in the fraction of quenched galaxies. While TNG colour distributions are clearly bimodal, this is not the case for the SFR logarithmic distributions in bins of stellar mass (SFR ≳ 10−3 M⊙yr−1). Finally, the slope and z  = 0 normalization of the TNG MS are consistent with observational findings; however, the locus of the TNG MS remains lower by about 0.2−0.5 dex at 0.75 ≤ z < 2 than the available observational estimates taken at face value. [ABSTRACT FROM AUTHOR]

We study the connection between active galactic nuclei (AGN) and their host galaxies through cosmic time in the large-scale cosmological IllustrisTNG simulations. We first compare BH properties, i.e. the hard X-ray BH luminosity function, AGN galaxy occupation fraction, and distribution of Eddington ratios, to available observational constraints. The simulations produce a population of BHs in good agreement with observations, but we note an excess of faint AGN in hard X-ray (⁠|$L_{\rm x}\sim 10^{43-44}\, \rm erg/s$|⁠), and a lower number of bright AGN (⁠|$L_{\rm x}\gt 10^{44} \, \rm erg/s$|⁠), a conclusion that varies quantitatively but not qualitatively with BH luminosity estimation method. The lower Eddington ratios of the |$10^{9}\, \rm M_{\odot }$| BHs compared to observations suggest that AGN feedback may be too efficient in this regime. We study galaxy star formation activity and structural properties, and design sample-dependent criteria to identify different galaxy types (star-forming/quiescent, extended/compact) that we apply both to the simulations and observations from the candels fields. We analyse how the simulated and observed galaxies populate the specific star formation rate – stellar mass surface density diagram. A large fraction of the |$z$|  = 0 |$M_{\star }\geqslant 10^{11}\, \rm M_{\odot }$| quiescent galaxies first experienced a compaction phase (i.e. reduction of galaxy size) while still forming stars, and then a quenching event. We measure the dependence of AGN fraction on galaxies' locations in this diagram. After correcting the simulations with a redshift and AGN luminosity-dependent model for AGN obscuration, we find good qualitative and quantitative agreement with observations. The AGN fraction is the highest among compact star-forming galaxies (⁠|$16-20{{\ \rm per\ cent}}$| at |$z$|  ∼ 1.5–2), and the lowest among compact quiescent galaxies (⁠|$6-10{{\ \rm per\ cent}}$| at |$z$|  ∼ 1.5–2). [ABSTRACT FROM AUTHOR]

The coevolution of galaxies and their metal content serves as an important test for galaxy feedback models. We analyse the distribution and evolution of metals within the IllustrisTNG simulation suite with a focus on the gas-phase mass−metallicity relation (MZR). We find that the IllustrisTNG model broadly reproduces the slope and normalization evolution of the MZR across the redshift range 0 < z < 2 and mass range 109 < M */M⊙ < 1010.5. We make predictions for the high-redshift (2 < z < 10) metal content of galaxies which is described by a gradual decline in the normalization of the metallicity with an average high-redshift (z > 2) evolution fit by d log(Z)/d z ≈ −0.064. Our simulations indicate that the metal retention efficiency of the interstellar medium (ISM) is low: a majority of gas-phase metals (∼85 per cent at z  = 0) live outside of the ISM, either in an extended gas disc, the circumgalactic medium, or outside the halo. Nevertheless, the redshift evolution in the simulated MZR normalization is driven by the higher gas fractions of high-redshift galaxies, not by changes to the metal retention efficiency. The scatter in the simulated MZR contains a clear correlation with the gas-mass or star formation rate of the system, in agreement with the observed fundamental metallicity relation. The scatter in the MZR is driven by a competition between periods of enrichment- and accretion-dominated metallicity evolution. We expect that while the normalization of the MZR declines with redshift, the slope of the correlation between metallicity and gas-mass at fixed stellar mass is not a strong function of redshift. Our results indicate that the gas fraction dependence of 'regulator' style models allows them to simultaneously explaining the shape, redshift evolution, and existence of correlated scatter with gas fraction about the MZR. [ABSTRACT FROM AUTHOR]

We investigate the influence of environment on the cold-gas properties of galaxies at |$z$|  = 0 within the TNG100 cosmological, magnetohydrodynamic simulation, part of the IllustrisTNG suite. We extend previous post-processing methods for breaking gas cells into their atomic and molecular phases, and build detailed mocks to comprehensively compare to the latest surveys of atomic hydrogen (H  i) in nearby galaxies, namely ALFALFA and xGASS. We use TNG100 to explore the H  i content, star formation activity, and angular momentum of satellite galaxies, each as a function of environment, and find that satellites are typically a factor of ≳3 poorer in H  i than centrals of the same stellar mass, with the exact offset depending sensitively on parent halo mass. Due to the large physical scales on which H  i measurements are made (∼45–245 kpc), contributions from gas not bound to the galaxy of interest but in the same line of sight crucially lead to larger H  i mass measurements in the mocks in many cases, ultimately aligning with observations. This effect is mass-dependent and naturally greater for satellites than centrals, as satellites are never isolated by definition. We also show that H  i stripping in TNG100 satellites is closely accompanied by quenching, in tension with observational data that instead favour that H  i is preferentially stripped before star formation is reduced. [ABSTRACT FROM AUTHOR]

We use the IllustrisTNG simulations to study the demographics and properties of jellyfish galaxies in the full cosmological context. By jellyfish galaxies, we mean satellites orbiting in massive groups and clusters that exhibit highly asymmetric distributions of gas and gas tails. In particular, we select TNG100 galaxies at low redshifts (⁠|$z$|  ≤ 0.6) with stellar mass exceeding |$10^{9.5} \, \mathrm{M_{\odot }}$| and with host halo masses in the range |$10^{13} \le M_{\rm 200c}/\, \mathrm{M_{\odot }}\le 10^{14.6}$|⁠. Among more than about 6000 (2600) galaxies with stars (and some gas), we identify 800 jellyfish galaxies by visually inspecting their gas and stellar mass maps in random projections. Namely, about 31 per cent of cluster satellites are found with signatures of ram-pressure stripping and gaseous tails stemming from their main luminous bodies. This is a lower limit: the random orientation entails a loss of about 30 per cent of galaxies that in an optimal projection would otherwise be identified as jellyfish. Furthermore, jellyfish galaxies are more frequent at intermediate and large cluster-centric distances (r / R 200c ≳ 0.25), in more massive hosts and at smaller satellite masses, and they typically orbit supersonically. The gaseous tails usually extend in opposite directions to the galaxy trajectory, with no relation between tail orientation and position of the host's centre. Finally, jellyfish galaxies are late infallers (<2.5–3 Gyr ago, at |$z$|  = 0) and the emergence of gaseous tails correlates well with the presence of bow shocks in the intracluster medium. [ABSTRACT FROM AUTHOR]

The galaxy Malin 1 contains the largest stellar disc known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity V max of 430 km s−1, contains a 100 kpc gas/stellar disc with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disc, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disc back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy discs as extreme as Malin 1 within the current galaxy formation framework. [ABSTRACT FROM AUTHOR]

We study the population of supermassive black holes (SMBHs) and their effects on massive central galaxies in the IllustrisTNG cosmological hydrodynamical simulations of galaxy formation. The employed model for SMBH growth and feedback assumes a two-mode scenario in which the feedback from active galactic nuclei occurs through a kinetic, comparatively efficient mode at low accretion rates relative to the Eddington limit, and in the form of a thermal, less efficient mode at high accretion rates. We show that the quenching of massive central galaxies happens coincidentally with kinetic-mode feedback, consistent with the notion that active supermassive black holes cause the low specific star formation rates observed in massive galaxies. However, major galaxy mergers are not responsible for initiating most of the quenching events in our model. Up to black hole masses of about $$10^{8.5}\, {\rm M}_{\odot}$$, the dominant growth channel for SMBHs is in the thermal mode. Higher mass black holes stay mainly in the kinetic mode and gas accretion is self-regulated via their feedback, which causes their Eddington ratios to drop, with SMBH mergers becoming the main channel for residual mass growth. As a consequence, the quasar luminosity function is dominated by rapidly accreting, moderately massive black holes in the thermal mode. We show that the associated growth history of SMBHs produces a low-redshift quasar luminosity function and a redshift zero black hole mass – stellar bulge mass relation is in good agreement with observations, whereas the simulation tends to overpredict the high-redshift quasar luminosity function. [ABSTRACT FROM AUTHOR]

We explore the abundance, spatial distribution, and physical properties of the OVI, OVII, and OVIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magnetohydrodynamical simulations. Modelling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshiftOVI column density distribution function (CDDF), and present its evolution for all three ions from z = 0 to z = 4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the OVI content of the CGM from COS-haloes and other low-redshift observations, producing columns as high as observed. We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 1011 < Mhalo/M⊙<1015 corresponding to 109 < M⊙/M⊙<1012 in stellar mass. Stacked radial profiles of OVI are computed in 3D number density and 2D projected column density, decomposing into 1-halo and 2-halo terms. Relating halo OVI to properties of the central galaxy, we find a correlation between the (g - r) colour of a galaxy and the total amount of OVI in its CGM. In comparison to the COS-Haloes finding, this leads to a dichotomy of columns around star-forming versus passive galaxies at fixed stellar (or halo) mass. We demonstrate that this correlation is a direct result of black hole feedback associated with quenching and represents a causal consequence of galactic-scale baryonic feedback impacting the physical state of the circumgalactic medium. [ABSTRACT FROM AUTHOR]

The fundamental metallicity relation (FMR) is a postulated correlation between galaxy stellar mass, star formation rate (SFR), and gas-phase metallicity. At its core, this relation posits that offsets from the mass–metallicity relation (MZR) at a fixed stellar mass are correlated with galactic SFR. In this Letter, we use hydrodynamical simulations to quantify the time-scales over which populations of galaxies oscillate about the average SFR and metallicity values at fixed stellar mass. We find that Illustris and IllustrisTNG predict that galaxy offsets from the star formation main sequence and MZR oscillate over similar time-scales, are often anticorrelated in their evolution, evolve with the halo dynamical time, and produce a pronounced FMR. Our models indicate that galaxies oscillate about equilibrium SFR and metallicity values – set by the galaxy's stellar mass – and that SFR and metallicity offsets evolve in an anticorrelated fashion. This anticorrelated variability of the metallicity and SFR offsets drives the existence of the FMR in our models. In contrast to Illustris and IllustrisTNG, we speculate that the SFR and metallicity evolution tracks may become decoupled in galaxy formation models dominated by feedback-driven globally bursty SFR histories, which could weaken the FMR residual correlation strength. This opens the possibility of discriminating between bursty and non-bursty feedback models based on the strength and persistence of the FMR – especially at high redshift. [ABSTRACT FROM AUTHOR]

We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colours of galaxies. We explore TNG100, a rerun of the original Illustris box, and TNG300, which includes 2 × 25003 resolution elements in a volume 20 times larger. Here, we present first results on the galaxy colour bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g - r) colours of 109 12.5 galaxies to the observed distribution from the Sloan Digital Sky Survey.We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement with the observations, with a sharp transition in median colour from blue to red at a characteristic M* ∼ 1010.5☉. Investigating the build-up of the colour-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy colour transition is supermassive black hole feedback in its low accretion state. Across the entire population the median colour transition time-scale Δtgreen is ∼1.6Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, redder galaxies have lower star formation rates, gas fractions, and gas metallicities; their stellar populations are also older and their large-scale interstellar magnetic fields weaker than in bluer galaxies. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M* >1011☉ which redden at z < 1 accumulate on average ∼25 per cent of their final z = 0 mass post-reddening; at the same time, ∼18 per cent of such massive galaxies acquire half or more of their final stellar mass while on the red sequence. [ABSTRACT FROM AUTHOR]

We introduce an updated physical model to simulate the formation and evolution of galaxies in cosmological, large-scale gravity+magnetohydrodynamical simulations with the moving mesh code AREPO. The overall framework builds upon the successes of the Illustris galaxy formation model, and includes prescriptions for star formation, stellar evolution, chemical enrichment, primordial and metal-line cooling of the gas, stellar feedback with galactic outflows, and black hole formation, growth and multimode feedback. In this paper, we give a comprehensive description of the physical and numerical advances that form the core of the IllustrisTNG (The Next Generation) framework. We focus on the revised implementation of the galactic winds, of which we modify the directionality, velocity, thermal content and energy scalings, and explore its effects on the galaxy population. As described in earlier works, the model also includes a new black-hole-driven kinetic feedback at low accretion rates, magnetohydrodynamics and improvements to the numerical scheme. Using a suite of (25Mpc h-1)3 cosmological boxes, we assess the outcome of the new model at our fiducial resolution. The presence of a selfconsistently amplified magnetic field is shown to have an important impact on the stellar content of 1012M⊙ haloes and above. Finally, we demonstrate that the new galactic winds promise to solve key problems identified in Illustris in matching observational constraints and affecting the stellar content and sizes of the low-mass end of the galaxy population. [ABSTRACT FROM AUTHOR]

The inefficiency of star formation in massive elliptical galaxies is widely believed to be caused by the interactions of an active galactic nucleus (AGN) with the surrounding gas. Achieving a sufficiently rapid reddening of moderately massive galaxies without expelling too many baryons has however proven difficult for hydrodynamical simulations of galaxy formation, prompting us to explore a new model for the accretion and feedback effects of supermassive black holes. For high-accretion rates relative to the Eddington limit, we assume that a fraction of the accreted rest mass energy heats the surrounding gas thermally, similar to the 'quasar mode' in previouswork. For low-accretion rates, we invoke a new, pure kinetic feedback model that imparts momentum to the surrounding gas in a stochastic manner. These two modes of feedback are motivated both by theoretical conjectures for the existence of different types of accretion flows as well as recent observational evidence for the importance of kinetic AGN winds in quenching galaxies.We find that a large fraction of the injected kinetic energy in this mode thermalizes via shocks in the surrounding gas, thereby providing a distributed heating channel. In cosmological simulations, the resulting model produces red, non-star-forming massive elliptical galaxies, and achieves realistic gas fractions, black hole growth histories and thermodynamic profiles in large haloes. [ABSTRACT FROM AUTHOR]