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Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of ∼3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

We study the dependence of fragmentation in massive gas-rich galaxy disks at$z > 1$ on feedback model and hydrodynamical method, employing the GASOLINE2SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. Wecompare non-cosmological galaxy disk runs with standard blastwave supernovae(SN)feedback, which introduces delayed cooling in order to drive winds, andruns with the new superbubble SN feedback, which produces winds naturally bymodelling the detailed physics of SN-driven bubbles and leads to efficientself-regulation of star formation. We find that, with blastwave feedback,massive star forming clumps form in comparable number and with very similarmasses in GASOLINE2 and GIZMO. The typical masses are in the range $10^7-10^8M_{\odot}$, lower than in most previous works, while giant clumps with massesabove $10^9 M_{\odot}$ are exceedingly rare. With superbubble feedback,instead, massive bound star forming clumps do not form because galaxies neverundergo a phase of violent disk instability. Only sporadic, unbound starforming overdensities lasting only a few tens of Myr can arise that aretriggered by perturbations of massive satellite companions. We conclude thatthere is a severe tension between explaining massive star forming clumpsobserved at $z > 1$ primarily as the result of disk fragmentation driven bygravitational instability and the prevailing view of feedback-regulated galaxyformation. The link between disk stability and star formation efficiency shouldthus be regarded as a key testing ground for galaxy formation theory.

Quasars powered by supermassive black holes (>108 M⊙) at z ∼ 6 are predicted to reside in cosmic overdense regions. However, observations so far could not confirm this expectation due to limited statistics. The picture is further complicated by the possible effects of quasar outflows (i.e. feedback) that could either suppress or stimulate the star formation rate (SFR) of companion galaxies, thus modifying the expected bias. Here, we quantify feedback effects on the properties and detectability of companions by comparing cosmological zoom-in simulations of a quasar in which feedback is either included or turned-off. With respect to the no-feedback case, companions (a) directly impacted by the outflow have their SFR increased by a factor of 2−3, and (b) tend to be more massive. Both effects shift the [C  ii ] 158  μ m and UV luminosity functions towards brighter magnitudes. This leads us to conclude that quasar feedback slightly increases the effective quasar bias, boosting the number density of observable quasar companions, in agreement with what has been found around the brightest quasars of recent Atacama Large Millimeter Array (ALMA) [C  ii ] surveys. Deeper observations performed with James Webb Space Telescope and/or ALMA will improve the statistical significance of this result by detecting a larger number of fainter quasar companions. [ABSTRACT FROM AUTHOR]

We use the magnetic-hydrodynamical simulation TNG50 to study the evolution of barred massive disc galaxies. Massive spiral galaxies are already present as early as z  = 4, and bar formation takes place already at those early times. The bars grow longer and stronger as the host galaxies evolve, with the bar sizes increasing at a pace similar to that of the disc scalelengths. The bar fraction mildly evolves with redshift for galaxies with |$M_{*}\ge 10^{10}\rm M_{\odot }$|⁠ , being greater than |$\sim 40{{\ \rm per\ cent}}$| at 0.5 < z < 3 and |$\sim 30{{\ \rm per\ cent}}$| at z  = 0. When bars larger than a given physical size (⁠|$\ge 2\, \rm kpc$|⁠) or the angular resolution limit of twice the I -band angular PSF FWHM of the HST are considered, the bar fraction dramatically decreases with increasing redshift, reconciling the theoretical predictions with observational data. We find that barred galaxies have an older stellar population, lower gas fractions, and star formation rates than unbarred galaxies. In most cases, the discs of barred galaxies assembled earlier and faster than the discs of unbarred galaxies. We also find that barred galaxies are typical in haloes with larger concentrations and smaller spin parameters than unbarred galaxies. Furthermore, the inner regions of barred galaxies are more baryon-dominated than those of unbarred galaxies but have comparable global stellar mass fractions. Our findings suggest that the bar population could be used as a potential tracer of the buildup of disc galaxies and their host haloes. With this paper, we release a catalogue of barred galaxies in TNG50 at six redshifts between z  = 4 and 0. [ABSTRACT FROM AUTHOR]

While massive black holes (MBHs) are known to inhabit all massive galaxies, their ubiquitous presence in dwarf galaxies has not been confirmed yet, with only a limited number of sources detected so far. Recently, some studies proposed infrared emission as an alternative way to identify MBHs in dwarfs, based on a similar approach usually applied to quasars. In this study, by accurately combining optical and infrared data taking into account resolution effects and source overlapping, we investigate in detail the possible limitations of this approach with current ground-based facilities, finding a quite low (∼0.4 per cent) fraction of active MBH in dwarfs that are luminous in mid-infrared, consistent with several previous results. Our results suggest that the infrared selection is strongly affected by several limitations that make the identification of MBHs in dwarf galaxies currently prohibitive, especially because of the very poor resolution compared to optical surveys, and the likely contamination by nearby sources, although we find a few good candidates worth further follow-ups. Optical, X-ray, and radio observations therefore still represent the most secure way to search for MBH in dwarfs. [ABSTRACT FROM AUTHOR]

Current galaxy observations suggest that a roughly linear correlation exists between the [C  ii ] emission and the star formation rate, either as spatially resolved or integrated quantities. Observationally, this correlation seems to be independent of metallicity, but the very large scatter does not allow to properly assess whether this is true. On the other hand, theoretical models tend to suggest a metallicity dependence of the correlation. In this study, we investigate the metallicity evolution of the correlation via a high-resolution zoom-in cosmological simulation of a dwarf galaxy employing state-of-the-art sub-grid modelling for gas cooling, star formation, and stellar feedback, and that self-consistently evolves the abundances of metal elements out of equilibrium. Our results suggest that the correlation should evolve with metallicity, in agreement with theoretical predictions, but also that this evolution can be hardly detected in observations, because of the large scatter. We also find that most of the [C  ii ] emission is associated with neutral gas at low-intermediate densities, whereas the highest emissivity is produced by the densest regions around star-forming regions. [ABSTRACT FROM AUTHOR]

Observations of high-redshift quasars provide information on the massive black holes (MBHs) powering them and the galaxies hosting them. Current observations of z ≳ 6 hosts, at sub-millimetre wavelengths, trace the properties of cold gas, and these are used to compare with the correlations between MBHs and galaxies characterizing the z  = 0 population. The relations at z  = 0, however, rely on stellar-based tracers of the galaxy properties. We perform a very high resolution cosmological zoom-in simulation of a z  = 7 quasar including state-of-the-art non-equilibrium chemistry, MBH formation, growth, and feedback, to assess the evolution of the galaxy host and the central MBH, and compare the results with recent ALMA observations of high-redshift quasars. We measure both the stellar-based quantities used to establish the z  = 0 correlations, as well as the gas-based quantities available in z ≳ 6 observations, adopting the same assumptions and techniques used in observational studies. The high-redshift studies argued that MBHs at high redshift deviate from the local MBH–galaxy correlations. In our analysis of the single galaxy we evolve, we find that the high-redshift population sits on the same correlations as the local one, when using the same tracers used at z  = 0. When using the gas-based tracers, however, MBHs appear to be overmassive. The discrepancy between local and high-redshift MBHs seems to be caused by the different tracers employed, and the necessary assumptions, and not by an intrinsic difference. Better calibration of the tracers, higher resolution data, and availability of facilities that can probe the stellar population will be crucial to assess precisely and accurately high-redshift quasar hosts. [ABSTRACT FROM AUTHOR]

Bars are a key factor in the long-term evolution of spiral galaxies, in their unique role in redistributing angular momentum and transporting gas and stars on large scales. The Eris-suite simulations are cosmological zoom-in, N -body, smoothed-particle hydrodynamic simulations built to follow the formation and evolution of a Milky-Way-sized galaxy across the build-up of the large-scale structure. Here we analyse and describe the outcome of two particular simulations taken from the Eris suite – ErisBH and Eris2k – which mainly differ in the prescriptions employed for gas cooling, star formation, and feedback from supernovae and black holes. Our study shows that the enhanced effective feedback in Eris2k, due to the collective effect of the different micro-physics implementations, results in a galaxy that is less massive than its ErisBH counterpart till z  ∼ 1. However, when the stellar content is large enough so that global dynamical instabilities can be triggered, the galaxy in Eris2k develops a stronger and more extended bar with respect to ErisBH. We demonstrate that the structural properties and time evolution of the two bars are very different. Our results highlight the importance of accurate sub-grid prescriptions in cosmological zoom-in simulations of the process of galaxy formation and evolution, and the possible use of a statistical sample of barred galaxies to assess the strength of the stellar feedback. [ABSTRACT FROM AUTHOR]

In this study, we present and validate a variation of recently developed physically motivated sub-grid prescriptions for supernova feedback that account for the unresolved energy-conserving phase of the bubble expansion. Our model builds upon the implementation publicly available in the mesh-less hydrodynamic code gizmo, and is coupled with the chemistry library krome. Here, we test it against different set-ups to address how it affects the formation/dissociation of molecular hydrogen (H2). First, we explore very idealized conditions, to show that it can accurately reproduce the terminal momentum of the blast-wave independent of resolution. Then, we apply it to a suite of numerical simulations of an isolated Milky Way-like galaxy and compare it with a similar run employing the delayed-cooling sub-grid prescription. We find that the delayed-cooling model, by pressurizing ad hoc the gas, is more effective in suppressing star formation. However, to get this effect, it must maintain the gas warm/hot at densities where it is expected to cool efficiently, artificially changing the thermo-chemical state of the gas, and reducing the H2 abundance even in dense gas. Mechanical feedback, on the other hand, is able to reproduce the H2 column densities without altering the gas thermodynamics, and, at the same time, drives more powerful outflows. However, being less effective in suppressing star formation, it overpredicts the Kennicutt–Schmidt relation by a factor of about 2.5. Finally, we show that the model is consistent at different resolution levels, with only mild differences. [ABSTRACT FROM AUTHOR]

By using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of 10 simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium; optically thin versus thick approximation), the initial gas metallicity (from 10 to 100 per cent solar), and how molecular hydrogen forms on dust. This is the first work in which metal injection from supernovae, turbulent metal diffusion, and a metal network with non-equilibrium metal cooling are self-consistently included in a galaxy simulation. We find that properly modelling the chemical evolution of several metal species and the corresponding non-equilibrium metal cooling has important effects on the thermodynamics of the gas, the chemical abundances, and the appearance of the galaxy: the gas is typically warmer, has a larger molecular-gas mass fraction, and has a smoother disc. We also conclude that, at relatively high metallicity, the choice of molecular-hydrogen formation rates on dust is not crucial. Moreover, we confirm that a higher initial metallicity produces a colder gas and a larger fraction of molecular gas, with the low-metallicity simulation best matching the observed molecular Kennicutt-Schmidt relation. Finally, our simulations agree quite well with observations that link star formation rate to metal emission lines. [ABSTRACT FROM AUTHOR]

We study the dynamical evolution of supermassive black holes, in the late stage of galaxy mergers, from kpc to pc scales. In particular,we capture the formation of the binary, a necessary step before the final coalescence, and trace back the main processes causing the decay of the orbit. We use hydrodynamical simulations of galaxy mergers with different resolutions, from 20 pc down to 1 pc, in order to study the effects of the resolution on our results, remove numerical effects, and assess that resolving the influence radius of the orbiting black hole is a minimum condition to fully capture the formation of the binary. Our simulations include the relevant physical processes, namely star formation, supernova feedback, accretion on to the black holes and the ensuing feedback. We find that, in these mergers, dynamical friction from the smooth stellar component of the nucleus is the main process that drives black holes from kpc to pc scales. Gas does not play a crucial role and even clumps do not induce scattering or perturb the orbits. We compare the time needed for the formation of the binary to analytical predictions and suggest how to apply such analytical formalism to obtain estimates of binary formation times in lower resolution simulations. [ABSTRACT FROM AUTHOR]

Numerical simulations have become a necessary tool to describe the complex interactions among the different processes involved in galaxy formation and evolution, unfeasible via an analytic approach. The last decade has seen a great effort by the scientific community in improving the sub-grid physics modelling and the numerical techniques used to make numerical simulations more predictive. Although the recently publicly available code GIZMO has proven to be successful in reproducing galaxy properties when coupled with the model of the MUFASA simulations and the more sophisticated prescriptions of the Feedback In Realistic Environment (FIRE) set-up, it has not been tested yet using delayed cooling supernova feedback, which still represent a reasonable approach for large cosmological simulations, for which detailed sub-grid models are prohibitive. In order to limit the computational cost and to be able to resolve the disc structure in the galaxies we perform a suite of zoom-in cosmological simulations with rather low resolution centred around a sub-L* galaxy with a halo mass of 3 × 1011 M☉ at z = 0, to investigate the ability of this simple model, coupled with the new hydrodynamic method of GIZMO, to reproduce observed galaxy scaling relations (stellar to halo mass, stellar and baryonic Tully-Fisher, stellar mass-metallicity and mass-size). We find that the results are in good agreement with the main scaling relations, except for the total stellar mass, larger than that predicted by the abundance matching technique, and the effective sizes for the most massive galaxies in the sample, which are too small. [ABSTRACT FROM AUTHOR]

Mergers of gas-rich galaxies are key events in the hierarchical built-up of cosmic structures, and can lead to the formation of massive black hole binaries. By means of high-resolution hydrodynamical simulations we consider the late stages of a gas-rich major merger, detailing the dynamics of two circumnuclear discs, and of the hosted massive black holes during their pairing phase. During the merger gas clumps with masses of a fraction of the black hole mass form because of fragmentation. Such high-density gas is very effective in forming stars, and the most massive clumps can substantially perturb the black hole orbits. After ~10 Myr from the start of the merger a gravitationally bound black hole binary forms at a separation of a few parsecs, and soon after, the separation falls below our resolution limit of 0.39 pc. At the time of binary formation the original discs are almost completely disrupted because of SNa feedback, while on pc scales the residual gas settles in a circumbinary disc with mass ~ 105 M⊙. We also test that binary dynamics is robust against the details of the SNa feedback employed in the simulations, while gas dynamics is not. We finally highlight the importance of the SNa time-scale on our results. [ABSTRACT FROM AUTHOR]

Numerical effects are known to plague adaptive mesh refinement (AMR) codes when treating massive particles, e.g. representing massive black holes (MBHs). In an evolving background, they can experience strong, spurious perturbations and then follow unphysical orbits. We study by means of numerical simulations the dynamical evolution of a pair MBHs in the rapidly and violently evolving gaseous and stellar background that follows a galaxy major merger. We confirm that spurious numerical effects alter the MBH orbits in AMR simulations, and show that numerical issues are ultimately due to a drop in the spatial resolution during the simulation, drastically reducing the accuracy in the gravitational force computation. We therefore propose a new refinement criterion suited for massive particles, able to solve in a fast and precise way for their orbits in highly dynamical backgrounds. The new refinement criterion we designed enforces the region around each massive particle to remain at themaximum resolution allowed, independently upon the local gas density. Such maximally resolved regions then follow the MBHs along their orbits, and effectively avoids all spurious effects caused by resolution changes. Our suite of high-resolution, AMR hydrodynamic simulations, including different prescriptions for the sub-grid gas physics, shows that the new refinement implementation has the advantage of not altering the physical evolution of the MBHs, accounting for all the non-trivial physical processes taking place in violent dynamical scenarios, such as the final stages of a galaxy major merger. [ABSTRACT FROM AUTHOR]