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Context. Molecular hydrogen (H2) plays a crucial role in the formation and evolution of galaxies, serving as the primary fuel reservoir for star formation. In a metal-enriched Universe, H2 forms mostly through catalysis on interstellar dust grain surfaces. However, due to the complexities of modelling this process, star formation in cosmological simulations often relies on empirical or theoretical frameworks that have only been validated in the local Universe to estimate the abundance of H2. Aims. The goal of this work is to model the connection between the processes of star, dust, and H2 formation in our cosmological simulations. Methods. Building upon our recent integration of a dust evolution model into the star formation and feedback model MUPPI, we included the formation of molecular hydrogen on the surfaces of dust grains. We also accounted for the destruction of molecules and their shielding from harmful radiation. Results. The model reproduces, reasonably well, the main statistical properties of the observed galaxy population for the stellar, dust, and H2 components. The evolution of the molecular hydrogen cosmic density (ρH2) in our simulated boxes peaks around redshift z = 1.5, consistent with observations. Following its peak, ρH2 decreases by a factor of two towards z = 0, which is a milder evolution than observed. Similarly, the evolution of the molecular hydrogen mass function since z = 2 displays a gentler evolution when compared to observations. Our model recovers satisfactorily the integrated molecular Kennicut-Schmidt (mKS) law between the surface star formation rate (ΣSFR) and surface H2 density (ΣH2) at z = 0. This relationship is already evident at z = 2, albeit with a higher normalization. We find hints of a broken power law with a steeper slope at higher ΣH2. We also study the H2-to-dust mass ratio in galaxies as a function of their gas metallicity and stellar mass, observing a decreasing trend with respect to both quantities. The H2-to-dust mass fraction for the global population of galaxies is higher at higher redshift. The analysis of the atomic-to-molecular transition on a particle-by-particle basis suggests that gas metallicity cannot reliably substitute the dust-to-gas ratio in models attempting to simulate dust-promoted H2. [ABSTRACT FROM AUTHOR]

Observations suggest that the amount of galactic dust in the Universe decreased by a factor of ∼2–3 during the last ∼8 Gyr. However, cosmological models of galaxy evolution usually struggle to explain this decrease. Here, we use the semi-analytic model (SAM) L-Galaxies2020 to show that this drop may be reproduced assuming standard prescriptions for dust production and evolution. We extend the SAM with (i) a state-of-the-art dust model that adopts the two-size approximation and (ii) a new disc instability criterion that triggers bulge and central black hole growth. The model reproduces some fundamental properties of the local galaxy population, such as the fraction of spheroid-dominated galaxies and some scaling relations involving dust. Moreover, the model predicts a galactic dust drop from z ∼ 1 → 0, which becomes closer to the observed one when adopting the new treatment of disc instabilities. This result is related to the newly implemented supermassive black hole growth during disc instabilities, which enhances the quenching of massive galaxies. Consequently, these objects feature a lower gas and dust content. We provide a census of the contribution of all the processes affecting the galactic dust content. Accretion is the dominant dust mass growth process. Destruction by supernovae, astration and ejection by winds have all a non-negligible role in decreasing the overall dust content in galaxies below z ∼ 1. We also discuss predictions concerning extra-galactic dust, confirming that a sputtering efficiency lower than the canonical one is required to match the few available observations. [ABSTRACT FROM AUTHOR]

The reservoir of molecular gas (H2) represents the fuel for the star formation (SF) of a galaxy. Connecting the star formation rate (SFR) to the available H2 is key to accurately model SF in cosmological simulations of galaxy formation. We investigate how modifying the underlying modelling of H2 and the description of stellar feedback in low-metallicity environments (LMF, i.e. low-metallicity stellar feedback) in cosmological zoomed-in simulations of a Milky Way-size halo influences the formation history of the forming, spiral galaxy, and its final properties. We exploit two different models to compute the molecular fraction of cold gas (⁠|$f_{\rm H_{2}}$|⁠): (i) the theoretical model by Krumholz et al. (2009b) and (ii) the phenomenological prescription by Blitz and Rosolowsky (2006). We find that the model adopted to estimate |$f_{\rm H_{2}}$| plays a key role in determining final properties and in shaping the morphology of the galaxy. The clumpier interstellar medium (ISM) and the more complex H2 distribution that the Krumholz et al. model predicts result in better agreement with observations of nearby disc galaxies. This shows how crucial it is to link the SFR to the physical properties of the star-forming, molecular ISM. The additional source of energy that LMF supplies in a metal-poor ISM is key in controlling SF at high redshift and in regulating the reservoir of SF across cosmic time. Not only is LMF able to regulate cooling properties of the ISM, but it also reduces the stellar mass of the galaxy bulge. These findings can foster the improvement of the numerical modelling of SF in cosmological simulations. [ABSTRACT FROM AUTHOR]

We study the evolution of dust in a cosmological volume using a hydrodynamical simulation in which the dust production is coupled with the MUPPI (MUlti Phase Particle Integrator) sub-resolution model of star formation and feedback. As for the latter, we keep as reference the model setup calibrated previously to match the general properties of Milky Way-like galaxies in zoom-in simulations. However, we suggest that an increase of the star formation efficiency with the local dust-to-gas ratio would better reproduce the observed evolution of the cosmic star formation density. Moreover, the paucity of quenched galaxies at low redshift demands a stronger role of active galactic nucleus feedback. We tune the parameters ruling direct dust production from evolved stars and accretion in the interstellar medium to get scaling relations involving dust, stellar mass and metallicity in good agreement with observations. In low-mass galaxies, the accretion process is inefficient. As a consequence, they remain poorer in silicate and small grains than higher mass ones. We reproduce reasonably well the few available data on the radial distribution of dust outside the galactic region, supporting the assumption that the dust and gas dynamics are well coupled at galactic scales. [ABSTRACT FROM AUTHOR]

We present cosmological zoom-in hydrodynamical simulations for the formation of disc galaxies, implementing dust evolution and dust promoted cooling of hot gas. We couple an improved version of our previous treatment of dust evolution, which adopts the two-size approximation to estimate the grain-size distribution, with the MUPPI star formation and feedback subresolution model. Our dust evolution model follows carbon and silicate dust separately. To distinguish differences induced by the chaotic behaviour of simulations from those genuinely due to different simulation set-up, we run each model six times, after introducing tiny perturbations in the initial conditions. With this method, we discuss the role of various dust-related physical processes and the effect of a few possible approximations adopted in the literature. Metal depletion and dust cooling affect the evolution of the system, causing substantial variations in its stellar, gas, and dust content. We discuss possible effects on the Spectral Energy Distribution of the significant variations of the size distribution and chemical composition of grains, as predicted by our simulations during the evolution of the galaxy. We compare dust surface density, dust-to-gas ratio, and small-to-large grain mass ratio as a function of galaxy radius and gas metallicity predicted by our fiducial run with recent observational estimates for three disc galaxies of different masses. The general agreement is good, in particular taking into account that we have not adjusted our model for this purpose. [ABSTRACT FROM AUTHOR]

We present simulations of galaxy formation, based on the gadget -3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for active galactic nucleus (AGN) feedback. Our sub-resolution model describes a multiphase interstellar medium (ISM), accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies (⁠|$M_{\rm halo,DM} \simeq 2 \times 10^{12}$|  M⊙, at z  = 0), to investigate: (i) the effect of different ways of coupling AGN feedback energy to the multiphase ISM; (ii) the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); (iii) how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive black holes (BHs) and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at z  = 0 is reduced by up to an order of magnitude, and the BH is prevented from accreting below z ≲ 2, when the galaxy disc forms. [ABSTRACT FROM AUTHOR]

Many massive star-forming disc galaxies in the redshift range 3–0.5 are observed to have a clumpy morphology showing giant clumps of size ~1 kpc and masses of about 107–1010 M⊙. The nature and fate of these giant clumps are still under debate. In this work, we use 19 high-resolution simulations of disc galaxies from the Numerical Investigations of Hundred Astrophysical Objects (NIHAO) sample to study the formation and evolution of clumps in the discs of high-redshift galaxies. We use mock Hubble Space Telescope-CANDELS observations created with the radiative transfer code GRASIL-3D to carry out, for the first time, a quantitative comparison of the observed fraction of clumpy galaxies and its evolution with redshift with simulations. We find a good agreement between the observed clumpy fraction and the one of the NIHAO galaxies. We find that dust attenuation can suppress intrinsically bright clumps and enhance less luminous ones. In our galaxy sample, we find clumps only in light (U band) from young stars but not in stellar mass surface density maps. This means that the NIHAO sample does not show clumpy stellar discs but rather a clumpy light distribution originating from clumpy star formation events. The clumps found in the NIHAO sample match observed age/colour gradients as a function of distance from the galaxy centre, but they show no sign of inward migration. Clumps in our simulations disperse on time-scales of about a hundred Myr and their contribution to bulge growth is negligible. [ABSTRACT FROM AUTHOR]

ABSTRACT We perform controlled numerical experiments to asses the effect of baryon mass loss on the inner structure of large galactic dark matter (DM) haloes. This mass expulsion is intended to mimic both the supernova and active galactic nucleus (AGN) feedbacks, as well as the evolution of stellar populations. This study is meant in particular for precursors of massive early-type galaxies (ETGs), wherein strong AGN feedback (often dubbed 'quasi-stellar object mode' in galaxy formation models) has been proposed to remove on a short time-scale, of the order of a few dynamical times, a substantial fraction of their baryons. In a previous paper we evaluated the observational consequences (size increase) of this process on the galactic structure. Here we focus on the distribution of DM in the galactic region. It is shown that the inner region of the DM halo expands and its density profile flattens by a sizeable amount, with little dependence on the expulsion time-scale. We also evaluate the effect of the commonly made approximation of treating the baryonic component as a potential that changes in intensity without any variation in shape. This approximation leads to some underestimates of the halo expansion and its slope flattening. We conclude that cuspy density profiles in ETGs could be difficult to reconcile with an effective AGN (or stellar) feedback during the evolution of these systems. [ABSTRACT FROM AUTHOR]

ABSTRACT A serious concern for semi-analytical galaxy formation models, aiming to simulate multiwavelength surveys and to thoroughly explore the model parameter space, is the extremely time-consuming numerical solution of the radiative transfer of stellar radiation through dusty media. To overcome this problem, we have implemented an artificial neural network (ANN) algorithm in the radiative transfer code grasil, in order to significantly speed up the computation of the infrared (IR) spectral energy distribution (SED). The ANN we have implemented is of general use, in that its input neurons are defined as those quantities effectively determining the shape of the IR SED. Therefore, the training of the ANN can be performed with any model and then applied to other models. We made a blind test to check the algorithm, by applying a net trained with a standard chemical evolution model (i.e. che_evo) to a mock catalogue extracted from the semi-analytic model morgana, and compared galaxy counts and evolution of the luminosity functions in several near-IR to sub-millimetre (sub-mm) bands, and also the spectral differences for a large subset of randomly extracted models. The ANN is able to excellently approximate the full computation, but with a gain in CPU time by ∼2 orders of magnitude. It is only advisable that the training covers reasonably well the range of values of the input neurons in the application. Indeed in the sub-mm at high redshift, a tiny fraction of models with some sensible input neurons out of the range of the trained net cause wrong answer by the ANN. These are extreme starbursting models with high optical depths, favourably selected by sub-mm observations, and are difficult to predict a priori. [ABSTRACT FROM AUTHOR]