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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 haloes. 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 time-scale 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 haloes, 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. [ABSTRACT FROM AUTHOR]

We present the to-date largest parameter space exploration of binaries in circumbinary discs (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 b,eq ∼ 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 b ≳ 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. [ABSTRACT FROM AUTHOR]

We present a suite of high-resolution hydrodynamic simulations of binaries immersed in circumbinary accretion discs (CBDs). For the first time, we investigate the preferential accretion rate as a function of both eccentricity e b and mass ratio q b in a densely sampled parameter space, finding that when compared with circular binaries, (i) mass ratios grow more efficiently in binaries on moderately eccentric orbits (0.0 ≲ e b ≲ 0.4), and (ii) high eccentricities (e b ≳ 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 time-scale, a potentially observable signature in accreting binaries with short orbital periods. We provide CBD locking angles and precession rates as a function of e b and q b for our simulation suite. [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]

Jets from supermassive black holes in the centres of galaxy clusters are a potential candidate for moderating gas cooling and subsequent star formation through depositing energy in the intracluster gas. In this work, we simulate the jet-intracluster medium interaction using the moving-mesh magnetohydrodynamics code AREPO. Our model injects supersonic, low-density, collimated and magnetized outflows in cluster centres, which are then stopped by the surrounding gas, thermalize and inflate low-density cavities filled with cosmic rays. We perform high-resolution, non-radiative simulations of the lobe creation, expansion and disruption, and find that its dynamical evolution is in qualitative agreement with simulations of idealized lowdensity cavities that are dominated by a large-scale Rayleigh-Taylor instability. The buoyant rising of the lobe does not create energetically significant small-scale chaotic motion in a volume-filling fashion, but rather a systematic upward motion in the wake of the lobe and a corresponding back-flow antiparallel to it. We find that, overall, 50 per cent of the injected energy ends up in material that is not part of the lobe, and about 25 per cent remains in the inner 100 kpc. We conclude that jet-inflated, buoyantly rising cavities drive systematic gas motions that play an important role in heating the central regions, while mixing of lobe material is subdominant. Encouragingly, the main mechanisms responsible for this energy deposition can be modelled already at resolutions within reach in future, high-resolution cosmological simulations of galaxy clusters. [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]

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]

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 14 massive quiescent galaxies ( log (M ⋆ / M ⊙) > 10 ) at z ∼ 2 selected from a representative sample of the Blue Jay survey. We reconstruct their star formation histories (SFHs) by fitting spectral energy distribution models to the JWST/NIRSpec R ∼ 1000 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); and (3) galaxies that are rapidly and recently quenched after a major starburst. Most recently quenched galaxies show neutral gas outflows, probed by blueshifted Na i D absorption, and ionized gas emission, with line ratios consistent with active galactic nucleus (AGN) diagnostics. This suggests that AGN activity drives multiphase 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 = (1.5–6.0) × 10−5 Mpc−3. The two old massive quiescent galaxies in our sample appear to have extremely early formation and quenching (z ≳ 6) and are possibly descendants of early post-starbursts at z > 3. These galaxies still show neutral gas reservoirs and weak H α emission, perhaps because the ejective AGN feedback that caused rapid quenching has weakened over time. [ABSTRACT FROM AUTHOR]

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]

Radio relics in galaxy clusters are extended synchrotron sources produced by cosmic-ray electrons in the microgauss 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 reaccelerated 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 active galactic nucleus 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 the 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. [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 present a post-processing catalogue 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⊙). We tag GC particles to all galaxies with stellar mass M * ≥ 5 × 106 M⊙, and we calibrate their masses to reproduce the observed power-law relation between GC mass and halo mass for galaxies with M 200 ≥ 1011 M⊙ (corresponding to M * ∼ 109 M⊙). Here, we explore whether an extrapolation of this M 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 |$\rm {\it M}_*=[5 \times 10^6 \rm {\!-\!} 10^9]$| M⊙ and observations. Moreover, we predict a steep decline in the GC occupation fraction for dwarfs with M * < 109 M⊙ that 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 * < 107.5 M⊙. Our simulations also reproduce available constraints on the abundance of intracluster GCs in Virgo and Centaurus A. These successes provide support to the hypothesis that the M 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 catalogues are publicly available as part of the IllustrisTNG data release. [ABSTRACT FROM AUTHOR]

We study gas inflows on to 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 neighbourhood 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 ≲3 × 103 M⊙. 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. [ABSTRACT FROM AUTHOR]

We explore implications of a range of black hole (BH) seeding prescriptions on the formation of the brightest |$z$| ≳ 6 quasars in cosmological hydrodynamic simulations. The underlying galaxy formation model is the same as in the IllustrisTNG simulations. Using constrained initial conditions, we study the growth of BHs in rare overdense regions (forming |$\gtrsim 10^{12}\, {\rm M}_{\odot }\,h^{-1}$| haloes by |$z$|  = 7) using a  (9 Mpc  h −1)3 simulated volume. BH growth is maximal within haloes that are compact and have a low tidal field. For these haloes, we consider an array of gas-based seeding prescriptions wherein |$M_{\mathrm{seed}}=10^4\!-\!10^6\, {\rm M}_{\odot }\,h^{-1}$| seeds are inserted in haloes 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 seed). We find that a seed model with |$\tilde{M}_{\mathrm{sf,mp}}=5$| and |$\tilde{M}_{\mathrm{h}}=3000$| successfully produces a |$z$| ∼ 6 quasar with |$\sim 10^9\, {\rm M}_{\odot }$| mass and ∼1047 erg s−1 luminosity. BH mergers play a crucial role at |$z$| ≳ 9, causing an early boost in BH mass at a time when accretion-driven BH growth is negligible. With more stringent seeding conditions (e.g. |$\tilde{M}_{\mathrm{sf,mp}}=1000$|⁠), the relative paucity of BH seeds results in a much lower merger rate. In this case, |$z$| ≳ 6 quasars can only be formed if we enhance the maximum allowed BH accretion rates (by factors ≳10) 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 demonstrate that progenitors of |$z$| ∼ 6 quasars have distinct BH merger histories for different seeding models, which will be distinguishable with Laser Interferometer Space Antenna observations. [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]

Direct collapse black holes (BHs) are promising candidates for producing massive z ≳ 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 (spin), 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 |$M_{\rm seed} \sim 10^4\!-\!10^6\, \mathrm{M}_{\odot }\, h^{-1})$| in haloes with a total mass >3000 × M seed and a dense, metal-poor gas mass >5 × M seed. Within this framework, we find that the seed-forming haloes have a prior history of star formation and metal enrichment, but they also contain pockets of dense, metal-poor gas. When seeding is further restricted to haloes with low gas spins, the number of seeds formed is suppressed by factors of ∼6 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 crit). Even for J crit values as low as 50 J 21, no |$8\times 10^{5}~\mathrm{M}_{\odot }\, h^{-1}$| seeds are formed. While lower mass (⁠|$1.25\times 10^{4},1\times 10^{5}~\mathrm{M}_{\odot }\, h^{-1}$|⁠) seeds do form, they are strongly suppressed (by factors of ∼10–100) compared to the baseline model at gas mass resolutions of |$\sim 10^4~\mathrm{M}_{\odot }\, h^{-1}$|  (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, none of the seeds are able to grow to the supermassive regime (⁠|$\gtrsim 10^6~\mathrm{M}_{\odot }\, h^{-1}$|⁠) by z  = 7. Our results hint that producing the bulk of the z ≳ 6 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. [ABSTRACT FROM AUTHOR]

We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final installment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as discy galaxies with stellar masses of |$M_* = 10^{10.5 - 11.2}~\rm {M}_\odot$| in relative isolation at z = 0. By defining satellites as galaxies with |$M_* \ge 5\times 10^{6}~\rm {M}_\odot$| within |$300~\rm {kpc}$| (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median TNG50 MW/M31-like galaxy hosts a total of |$5^{+6}_{-3}$| satellites with |$M_* \ge 8 \times 10^6~\rm {M}_\odot$|⁠ , reaching up to |$M_* \sim 10^{8.5^{+0.9}_{-1.1}}~\rm {M}_\odot$|⁠. Even at a fixed host halo mass of |$10^{12}~\rm {M}_\odot$|⁠ , the total number of satellites ranges between 0 and 11. The abundance of subhaloes with |$M_\rm {dyn} \ge 5 \times 10^7~\rm {M}_\odot$| 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, more recent halo assembly, and – most significantly – larger total halo mass typically have a larger number of surviving satellites. The satellite abundances around TNG50 MW/M31-like galaxies are consistent with those of mass-matched 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 1σ scatter but well consistent with the high-mass end of the TNG50 sample. We find a handful of systems with both a Large and a Small Magellanic Cloud-like satellite. There is no missing satellites problem according to TNG50. [ABSTRACT FROM AUTHOR]

Deciphering the formation of supermassive black holes (SMBHs) is a key science goal for upcoming observational facilities. In many 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 |$M_{\mathrm{seed}}\sim 10^3\!-\!10^{6}~\mathrm{M}_{\odot }\, h^{-1}$| are placed in haloes 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 seed). We quantify the impact of these parameters on the properties of z ≥ 7 SMBHs. Lower seed masses produce higher black hole merger rates (by factors of ∼10 and ∼1000 at z ∼ 7 and z ∼ 15, respectively). For fixed seed mass, we find that |$\tilde{M}_{\mathrm{h}}$| has the strongest impact on the black hole population at high redshift (z ≳ 15, where a factor of 10 increase in |$\tilde{M}_{\mathrm{h}}$| suppresses merger rates by ≳100). At lower redshift (z ≲ 15), we find that |$\tilde{M}_{\mathrm{sf,mp}}$| has a larger impact on the black hole population. Increasing |$\tilde{M}_{\mathrm{sf,mp}}$| from 5 to 150 suppresses the merger rates by factors of ∼8 at z ∼ 7–15. This suggests that the seeding criteria explored here could leave distinct imprints on LISA merger rates. In contrast, AGN luminosity functions are much less sensitive to seeding criteria, varying by factors ≲2–3 within our models. Such variations will be challenging to probe even with future sensitive instruments such as Lynx or JWST. Our study provides a useful benchmark for development of seed models for large-volume cosmological simulations. [ABSTRACT FROM AUTHOR]

To break the degeneracy among galactic stellar components, we extract kinematic structures using the framework that was described in Du et al. 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 1010âˆ'11.5 M ⊙ from the TNG50 simulation, we identify three broadly-defined types of galaxies: galaxies 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. By tracing galaxies back in time, we recognize three fundamental regimes: an early phase of evolution (z ≳ 2), 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 ∼ 2. The difference in their present-day structures originates from two distinct evolutionary pathwaysâ€"extended versus compactâ€"that are likely to be determined by their parent dark matter halos (i.e., nature). In contrast, 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. [ABSTRACT FROM AUTHOR]

We investigate the morphology of the stellar distribution (SD) in a sample of Milky Way–like galaxies in the TNG50 simulation. Using a local in shell iterative method as the main approach, we explicitly show evidence of twisting (in about 52% of halos) and stretching (in 48% of them) in real space. This is matched with the reorientation observed in the eigenvectors of the inertia tensor and gives us a clear picture of having a reoriented SD. We make a comparison between the shape profile of the dark matter (DM) halo and SD 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, faraway substructures are counterrotating 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 on the observational constraints from previous literature, we establish fair agreement. [ABSTRACT FROM AUTHOR]

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, we infer an oblate-to-triaxial shape for the DM halo with median T ≃ 0.24. We group DM halos into three different categories. Simple halos (32% of the 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%) experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36%) demonstrate a stretching in the lengths of their principal axes where the ordering of different eigenvalues changes with radius. Subsequently, the halo experiences a "rotation" of ∼90° where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of a reorienting 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 impacts of substructure on DM halo shape in both hydrodynamical and DMO simulations and confirm that they are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle between satellites' angular momentum and the 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. [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]

We study black hole–host galaxy correlations, and the relation between the overmassiveness (the distance from the average MBH–σ relation) of supermassive black holes (SMBHs) and the 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 MBH–σ relation, and the relation between MBH and the Sérsic index. The relation between MBH and stellar mass M* is tighter than the observations, especially for TNG100. For massive galaxies in both simulations, the hosts of overmassive SMBHs (those above the mean MBH–σ relation) tend to have larger Sérsic indices and lower baryon conversion efficiency, suggesting a multidimensional link between SMBHs and the properties of their hosts. In Illustris, the hosts of overmassive SMBHs have formed earlier and have lower present-day star formation rates, in qualitative agreement with the observations for massive galaxies with σ > 100 km s−1. 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 overmassiveness and star formation history is much weaker. The hosts of overmassive SMBHs generally have consistently larger star formation rates throughout history. These galaxies have higher stellar mass as well, due to the strong MBH–M* correlation. Our findings show that simulated SMBH scaling relations and correlations are sensitive to features in the modeling of SMBHs. [ABSTRACT FROM AUTHOR]

Hot gaseous atmospheres that permeate galaxies and extend far beyond their stellar distribution, where they are commonly referred to as the circumgalactic medium, imprint important information about feedback processes powered by the stellar populations of galaxies and their central supermassive black holes (SMBHs). 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 X) and temperature (T X) at small (< R e) and intermediate (<5 R e) radii reasonably well. We find that the X-ray properties of lower mass galaxies depend on their star formation rates. In particular, in the magnitude range where the star-forming and quenched populations overlap, |$M_{\rm K}\sim -24\ (M_*\sim 10^{10.7}\, \mathrm{M}_\odot)$|⁠ , we find that the X-ray luminosities of star-forming galaxies are on average about an order of magnitude higher than those of their quenched counterparts. We show that this diversity in L X is a direct manifestation of the quenching mechanism in the simulations, where the galaxies are quenched due to gas expulsion driven by SMBH kinetic feedback. The observed dichotomy in L X is thus an important observable prediction for the SMBH feedback-based quenching mechanisms implemented in state-of-the-art cosmological simulations. While the current X-ray observations of star-forming galaxies are broadly consistent with the predictions of the simulations, the observed samples are small and more decisive tests are expected from the sensitive all-sky X-ray survey with eROSITA. [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 explore the isothermal total density profiles of early-type galaxies (ETGs) in the IllustrisTNG simulation. For the selected 559 ETGs at z  = 0 with stellar masses |$10^{10.7}\, \mathrm{M}_{\odot } \leqslant M_{\ast } \leqslant 10^{11.9}\, \mathrm{M}_{\odot }$|⁠ , the total power-law slope has a mean of 〈γ′〉 = 2.011 ± 0.007 and a scatter of |$\sigma _{\gamma ^{\prime }} = 0.171$| over the radial range 0.4–4 times the stellar half-mass radius. Several correlations between γ′ and galactic properties including stellar mass, effective radius, stellar surface density, central velocity dispersion, central dark matter fraction, and in situ -formed stellar mass ratio are compared to observations and other simulations, revealing that IllustrisTNG reproduces many correlation trends, and in particular, γ′ is almost constant with redshift below z  = 2. Through analysing IllustrisTNG model variations, we show that black hole kinetic winds are crucial to lowering γ′ and matching observed galaxy correlations. The effects of stellar winds on γ′ are subdominant compared to active galactic nucleus (AGN) feedback, and differ due to the presence of AGN feedback from previous works. The density profiles of the ETG dark matter haloes are well described by steeper than NFW profiles, and they are steeper in the full physics (FP) run than their counterparts in the dark matter-only (DMO) run. Their inner density slopes anticorrelate (remain constant) with the halo mass in the FP (DMO) run, and anticorrelate with the halo concentration parameter c 200 in both the types of runs. The dark matter haloes of low-mass ETGs are contracted whereas high-mass ETGs are expanded, suggesting that variations in the total density profile occur through the different halo responses to baryons. [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 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]

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 of |$M_{*}/\mathrm{M}_{\odot }\in [10^{9.7},\, 10^{11.4}]$| 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 dependences. In particular, the mean mass dependences 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 |$M_{*}\approx 1\rm {-}2\times 10^{10}\, \mathrm{M}_{\odot }$| 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) |$M_{*}\approx 6\times 10^{10}\, \mathrm{M}_{\odot }$| are systematically higher than the observational data by |$\lesssim 10{{\ \rm per\ cent}}$| (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. [ABSTRACT FROM AUTHOR]

Understanding how baryonic processes shape the intracluster medium (ICM) is of critical importance to the next generation of galaxy cluster surveys. However, many models of structure formation neglect potentially important physical processes, like anisotropic thermal conduction (ATC). We explore the impact of ATC on the prevalence of cool-cores (CCs) via 12 pairs of magnetohydrodynamical galaxy cluster simulations, using the IllustrisTNG model with and without ATC. Examining their properties we find that the addition of ATC has a negligible impact on the median rotation measure, plasma β, the magnetic field-radial direction angle, and the effective Spitzer value. However, the scatter in the angle and effective Spitzer value is 50 per cent larger with ATC because the magnetic field aligns with the azimuthal direction to a greater extent in relaxed clusters. ATC's impact varies from cluster to cluster and with CC criterion, but its inclusion produces a systematic shift to larger CC fractions at z = 0 for all CC criteria considered. Additionally, the inclusion of ATC flattens the CC fraction redshift evolution, helping to ease the tension with the observed evolution. With ATC, the energy required for the central black hole to self-regulate is reduced by 24 per cent and the gas fraction at |$0.01\, r_{500}$| increases by 100 per cent, producing larger CC fractions. ATC makes the ICM unstable to perturbations and the increased efficiency of AGN feedback suggests that its inclusion results in a greater level of mixing in the ICM, demonstrated by the 10 per cent reduction in central metallicity for clusters with ATC. [ABSTRACT FROM AUTHOR]

We analyse the IllustrisTNG simulations to study the mass, volume fraction, and phase distribution of gaseous baryons embedded in the knots, filaments, sheets, and voids of the Cosmic Web from redshift z  = 8 to redshift z  = 0. We find that filaments host more star-forming gas than knots, and that filaments also have a higher relative mass fraction of gas in this phase than knots. We also show that the cool, diffuse intergalactic medium [IGM; |$T\lt 10^5 \, {\rm K}$|⁠ , |$n_{\rm H}\lt 10^{-4}(1+z) \, {\rm cm^{-3}}$| ] and the warm-hot intergalactic medium [WHIM; |$10^5 \lt T\lt 10^7 \, {\rm K}$|⁠ , |$n_{\rm H} \lt 10^{-4}(1+z)\, {\rm cm^{-3}}$| ] constitute |${\sim } 39$| and |${\sim } 46{{\ \rm per\ cent}}$| of the baryons at redshift z  = 0, respectively. Our results indicate that the WHIM may constitute the largest reservoir of missing baryons at redshift z  = 0. Using our Cosmic Web classification, we predict the WHIM to be the dominant baryon mass contribution in filaments and knots at redshift z  = 0, but not in sheets and voids where the cool, diffuse IGM dominates. We also characterize the evolution of WHIM and IGM from redshift z  = 4 to redshift z  = 0, and find that the mass fraction of WHIM in filaments and knots evolves only by a factor of ∼2 from redshift z  = 0 to 1, but declines faster at higher redshift. The WHIM only occupies |$4\!-\!11{{\ \rm per\ cent}}$| of the volume at redshift 0 ≤ z ≤ 1. We predict the existence of a significant number of currently undetected O  vii and Ne  ix absorption systems in cosmic filaments, which could be detected by future X-ray telescopes like Athena. [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 have generated synthetic images of ∼27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log10(M */M⊙) ≈ 9.8–11.3 galaxies at |$z$|  ≈ 0.05. Most of our synthetic images were created with the skirt radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves. We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics – including the Gini– M 20 and concentration–asymmetry–smoothness statistics – and performs 2D Sérsic fits. Overall, we find that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation. In particular, the locus of the Gini– M 20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the morphological, size and shape parameters considered in this work lie within the ∼1σ scatter of the observational trends. However, the IllustrisTNG model has some difficulty with more stringent tests, such as producing a strong morphology–colour relation. This results in a somewhat higher fraction of red discs and blue spheroids compared to observations. Similarly, the morphology–size relation is problematic: while observations show that discs tend to be larger than spheroids at a fixed stellar mass, such a trend is not present in IllustrisTNG. [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]

We use the IllustrisTNG (TNG) cosmological simulations to provide theoretical expectations for the dark matter mass fractions (DMFs) and circular velocity profiles of galaxies. TNG predicts flat circular velocity curves for |$z$| = 0 Milky Way (MW)-like galaxies beyond a few kpc from the galaxy centre, in better agreement with observational constraints than its predecessor, Illustris. TNG also predicts an enhancement of the dark matter mass within the 3D stellar half-mass radius (⁠|$r_{\rm half}$|⁠ ; |$M_{\rm 200c} = 10^{10}-10^{13}\, \mathrm{M_{\odot }}$|⁠, |$z$| ≤ 2) compared to its dark matter only and Illustris counterparts. This enhancement leads TNG present-day galaxies to be dominated by dark matter within their inner regions, with |$f_{\rm DM}(\lt r_{\rm half})\gtrsim 0.5$| at all masses and with a minimum for MW-mass galaxies. The 1σ scatter is ≲10 per cent at all apertures, which is smaller than that inferred by some observational data sets, e.g. 40 per cent from the sluggs survey. TNG agrees with the majority of the observationally inferred values for elliptical galaxies once a consistent initial mass function is adopted (Chabrier) and the DMFs are measured within the same apertures. The DMFs measured within |$r_{\rm half}$| increase towards lower redshifts: this evolution is dominated by the increase in galaxy size with time. At |$z$| ∼ 2, the DMF in disc-like TNG galaxies decreases with increasing galaxy mass, with |$f_{\rm DM}(\lt r_{\rm half}) \sim 0.10\hbox{--}0.65$| for 1010≲ M stars/M |$\odot$| ≲ 1012, and are two times higher than if TNG galaxies resided in Navarro–Frenk–White dark matter haloes unaffected by baryonic physics. It remains to be properly assessed whether recent observational estimates of the DMFs at |$z$| ∼ 2 rule out the contraction of the dark matter haloes predicted by the TNG model. [ABSTRACT FROM AUTHOR]

The thermodynamic structure of hot gas in galaxy clusters is sensitive to astrophysical processes and typically difficult to model with galaxy formation simulations. We explore the fraction of cool-core (CC) clusters in a large sample of 370 clusters from IllustrisTNG, examining six common CC definitions. IllustrisTNG produces continuous CC criteria distributions, the extremes of which are classified as CC and non-cool core (NCC), and the criteria are increasingly correlated for more massive clusters. At |$z$| = 0, the CC fractions for two criteria are in reasonable agreement with the observed fractions but the other four CC fractions are lower than observed. This result is partly driven by systematic differences between the simulated and observed gas fraction profiles. The simulated CC fractions with redshift show tentative agreement with the observed fractions, but linear fits demonstrate that the simulated evolution is steeper than observed. The conversion of CCs to NCCs appears to begin later and act more rapidly in the simulations. Examining the fraction of CCs and NCCs defined as relaxed we find no evidence that CCs are more relaxed, suggesting that mergers are not solely responsible for disrupting CCs. A comparison of the median thermodynamic profiles defined by different CC criteria shows that the extent to which they evolve in the cluster core is dependent on the CC criteria. We conclude that the thermodynamic structure of galaxy clusters in IllustrisTNG shares many similarities with observations, but achieving better agreement most likely requires modifications of the underlying galaxy formation model. [ABSTRACT FROM AUTHOR]

We introduce the IllustrisTNG project, a new suite of cosmological magnetohydrodynamical simulations performed with the moving-mesh code arepo employing an updated Illustris galaxy formation model. Here we focus on the general properties of magnetic fields and the diffuse radio emission in galaxy clusters. Magnetic fields are prevalent in galaxies, and their build-up is closely linked to structure formation. We find that structure formation amplifies the initial seed fields (10−14 comoving Gauss) to the values observed in low-redshift galaxies (⁠|$1\hbox{--}10\, {\rm \mu G}$|⁠). The magnetic field topology is closely connected to galaxy morphology such that irregular fields are hosted by early-type galaxies, while large-scale, ordered fields are present in disc galaxies. Using two simple models for the energy distribution of relativistic electrons we predict the diffuse radio emission of 280 clusters with a baryonic mass resolution of |$1.1\times 10^{7}\, {\rm M_{\odot }}$|⁠, and generate mock observations for Very Large Array (VLA), Low-Frequency Array (LOFAR), Australian Square Kilometre Array Pathfinder (ASKAP), and Square Kilometre Array (SKA). Our simulated clusters show extended radio emission, whose detectability correlates with their virial mass. We reproduce the observed scaling relations between total radio power and X-ray emission, M 500, and the Sunyaev-Zel'dovich Y 500 parameter. The radio emission surface brightness profiles of our most massive clusters are in reasonable agreement with VLA measurements of Coma and Perseus. Finally, we discuss the fraction of detected extended radio haloes as a function of virial mass and source count functions for different instruments. Overall our results agree encouragingly well with observations, but a refined analysis requires a more sophisticated treatment of relativistic particles in large-scale galaxy formation simulations. [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]

The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the elemental distributions of stars in the IllustrisTNG simulations. We analyse the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses log (M*/M⊙) ~ 9.7-11.2). Comparison of observed magnesium and europium for individual stars in the Milky Way with the stellar abundances in our more than 850 Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. Here, we use the magnesium-to-iron ratio as a proxy for the effects of our SNII (core-collapse supernovae) and SNIa (Type Ia supernovae) metal return prescription and as a comparison to a variety of galactic observations. The europium-to-iron ratio tracks the rare ejecta from neutron star-neutron star mergers, the assumed primary site of europium production in our models, and is a sensitive probe of the effects of metal diffusion within the gas in our simulations. We find that europium abundances in MilkyWay-like galaxies show no correlation with assembly history, present-day galactic properties, and average galactic stellar population age. We reproduce the europium-to-iron spread at low metallicities observed in the Milky Way, and find it is sensitive to gas properties during redshifts z ≈ 2-4. We show that while the overall normalization of [Eu/Fe] is susceptible to resolution and post-processing assumptions, the relatively large spread of [Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is quite robust. [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]