ABSTRACT
We present a new implementation of the GAlaxy Evolution and Assembly (gaea) semi-analytic model, that features an improved modelling of the process of cold gas accretion on to supermassive ...black hole (SMBHs), derived from both analytic arguments and high-resolution simulations. We consider different scenarios for the loss of angular momentum required for the available cold gas to be accreted on to the central SMBHs, and we compare different combinations of triggering mechanisms, including galaxy mergers and disc instabilities in star-forming discs. We compare our predictions with the luminosity function (LF) observed for active galactic nuclei (AGNs) and we confirm that a non-instantaneous accretion time-scale (either in the form of a low-angular momentum reservoir or as an assumed light-curve evolution) is needed in order to reproduce the measured evolution of the AGN-LF and the so-called AGN-downsizing trend. Moreover, we also study the impact of AGN feedback, in the form of AGN-driven outflows, on the SF properties of model galaxies, using prescriptions derived both from empirical studies and from numerical experiments. We show that AGN-driven outflows are effective in suppressing the residual star formation rate in massive galaxies (>1011 M⊙) without changing their overall assembly history. These winds also affect the SFR of lower mass galaxies, resulting in a too large fraction of passive galaxies at <1010 M⊙. Finally, we study the Eddington ratio distribution as a function of SMBH mass, showing that only objects more massive than 108 M⊙ are already in a self-regulated state as inferred from observations.
The First Quenched Galaxies: When and How? Xie 谢, Lizhi 利智; De Lucia, Gabriella; Fontanot, Fabio ...
Astrophysical journal. Letters,
05/2024, Letnik:
966, Številka:
1
Journal Article
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Abstract Many quiescent galaxies discovered in the early Universe by JWST raise fundamental questions on when and how these galaxies became and stayed quenched. Making use of the latest version of ...the semianalytic model GAEA that provides good agreement with the observed quenched fractions up to z ∼ 3, we make predictions for the expected fractions of quiescent galaxies up to z ∼ 7 and analyze the main quenching mechanism. We find that in a simulated box of 685 Mpc on a side, the first quenched massive ( M ⋆ ∼ 10 11 M ⊙ ), Milky Way–mass, and low-mass ( M ⋆ ∼ 10 9.5 M ⊙ ) galaxies appear at z ∼ 4.5, z ∼ 6.2, and before z = 7, respectively. Most quenched galaxies identified at early redshifts remain quenched for more than 1 Gyr. Independently of galaxy stellar mass, the dominant quenching mechanism at high redshift is accretion disk feedback (quasar winds) from a central massive black hole, which is triggered by mergers in massive and Milky Way–mass galaxies and by disk instabilities in low-mass galaxies. Environmental stripping becomes increasingly more important at lower redshift.
We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are ...able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into `passive' and `star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift.
Deviations from a universal, Milky Way-like, Stellar initial mass function (IMF) have been reported for distant galaxies, although the physical reason behind the observed variations is still matter ...of ongoing debate. In this paper, we present an exploratory study to assess the impact of the proposed IMF evolution on the statistical galaxy properties, as predicted by the semi-analytical model of galaxy formation and evolution MOdel for the Rise of Galaxies aNd Agns (morgana). In particular, we test different dependences for the IMF shape, as a function of both model galaxy properties (such as star formation rate, velocity dispersion or stellar mass) and environment, and compare the predicted stellar mass functions and star formation rate functions with reference runs at fixed IMF. In most cases, morgana predictions show deviations of the order of a few tenths of dex with respect to a run assuming a universal Kroupa IMF. Among the proposed IMF variations, an increasing top-heavy IMF at increasing star formation rates has the largest impact on predicted galaxy properties, while most of the models assuming an increasing bottom-heavy IMF at higher masses/velocity dispersion lead to variations in galaxy properties that are of the same order as the uncertainty on the mass and star formation rate determination. By comparing the predicted galaxy stellar mass functions, we conclude that the study of the high-mass end can provide useful constraints to disentangle models assuming an increasing top-heavy IMF in high star forming or bottom-heavy IMF in massive systems.
In order to constrain the physical processes that regulate and downsize the active galactic nucleus (AGN) population, the predictions of the model for the rise of galaxies and active nuclei (morgana) ...are compared to luminosity functions (LFs) of AGNs in the optical, soft and hard X-ray bands, to the local black hole (BH)–bulge mass relation and to the observed X-ray number counts and background. We also give predictions on the accretion rate of AGNs in units of the Eddington rate and on the BH–bulge relation expected at high redshift. We find that it is possible to reproduce the downsizing of AGNs within the hierarchical Lambda cold dark matter cosmogony and that the most likely cause of this downsizing is the stellar kinetic feedback that arises in star-forming bulges as a consequence of the high level of turbulence and leads to a massive removal of cold gas in small elliptical galaxies. At the same time, to obtain good fits to the number of bright quasars we require that quasar-triggered galactic winds self-limit the accretion on to BHs; however, the very high degree of complexity of the physics of these winds, coupled with our poor understanding of it, hampers more robust conclusions. In all cases, the predicted BH–bulge relation steepens considerably with respect to the observed one at bulge masses <1011 M⊙; this problem is related to a known excess in the predicted number of small bulges, common to most similar models, so that the reproduction of the correct number of faint AGNs is done at the cost of underestimating their BH masses. This highlights an insufficient downsizing of elliptical galaxies, and hints at another feedback mechanism able to act on the compact discs that form and soon merge at high redshift. The results of this paper reinforce the need for direct investigations of the feedback mechanisms in active galaxies that will be possible with the next generation of astronomical telescopes from submm to X-rays.
One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently ‘anti-hierarchical’ evolution of galaxy assembly: massive galaxies appear ...to be in place since z ∼ 3, while a significant increase of the number densities of low-mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of gaea, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological ‘FIRE’ simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60–70 per cent of the baryons reside in an ‘ejected’ reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.
A wealth of observations recently challenged the notion of a universal stellar initial mass function (IMF) by showing evidences in favour of a variability of this statistical indicator as a function ...of galaxy properties. I present predictions from the semi-analytic model gaea (GAlaxy Evolution and Assembly), which features (a) a detailed treatment of chemical enrichment, (b) an improved stellar feedback scheme, and (c) implements theoretical prescriptions for IMF variations. Our variable IMF realizations predict intrinsic stellar masses and mass-to-light ratios larger than those estimated from synthetic photometry assuming a universal IMF. This provides a self-consistent interpretation for the observed mismatch between photometrically inferred stellar masses of local early-type galaxies and those derived by dynamical and spectroscopic studies. At higher redshifts, the assumption of a variable IMF has a deep impact on our ability to reconstruct the evolution of the galaxy stellar mass function and the star formation history of galaxies.
Abstract
We take advantage of our recently published model for GAlaxy Evolution and Assembly (GAEA) to study the origin of the observed correlation between α/Fe and galaxy stellar mass. In ...particular, we analyse the role of radio-mode active galactic nuclei (AGN) feedback, which recent work has identified as a crucial ingredient to reproduce observations. In GAEA, this process introduces the observed trend of star formation histories extending over shorter time-scales for more massive galaxies, but does not provide a sufficient condition to reproduce the observed α enhancements of massive galaxies. In the framework of our model, this is possible only by assuming that any residual star formation is truncated for galaxies more massive than 1010.5 M⊙. This results, however, in even shorter star formation time-scales for the most massive galaxies, which translate in total stellar metallicities significantly lower than observed. Our results demonstrate that (i) trends of α/Fe ratios cannot be simply converted into relative time-scale indicators; and (ii) AGN feedback cannot explain alone the positive correlation between α/Fe and galaxy mass/velocity dispersion. Reproducing simultaneously the mass–metallicity relation and the α enhancements observed pose a challenge for hierarchical models, unless more exotic solutions are adopted such as metal-rich winds or a variable initial mass function.
We present the latest version of the GAlaxy Evolution and Assembly (GAEA) theoretical model of galaxy formation. Our new model now combines (i) an updated treatment of feedback from active galactic ...nuclei, including an improved modelling of cold gas accretion on super-massive black holes and an explicit implementation of quasar winds; and (ii) a treatment for both cold and hot gas stripping from satellite galaxies. We show that our latest model version predicts specific star formation rate distributions that are in remarkable agreement with observational measurements in the local Universe. Our updated model predicts quenched fractions that are in very nice agreement with observational measurements up to z ∼ 3 − 4, and a turn-over of the number densities of quenched galaxies at low stellar masses that is in qualitative agreement with current observational estimates. We show that the main reasons for the improved behaviour with respect to previous renditions of our model are the updated treatment for satellites at low galaxy masses (< 10 10 M ⊙ ) and the inclusion of quasar winds at intermediate to large stellar masses (> 10 10 M ⊙ ). However, we show that the better treatment of the star formation threshold, due to our explicit partitioning of the cold gas in its atomic and molecular components, also plays an important role in suppressing excessive residual star formation in massive galaxies. While our analysis is based on a selection of quiescent galaxies that takes advantage of the information about their star formation rate, we demonstrate that the impact of a different (colour-colour) selection is not significant up to z ∼ 3, at least for galaxies above the completeness limits of current surveys. Our new model predicts number densities of massive quiescent galaxies at z > 3 that are the largest among recently published state-of-the-art models. Yet, our model predictions still appear to be below post-JWST observational measurements. We show that the expected cosmic variance is large, and can easily accommodate some of the most recent measurements.
ABSTRACT
Reproducing the observed quenched fraction of satellite galaxies has been a long-standing issue for galaxy formation models. We modify the treatment of environmental effects in our ...state-of-the-art GAlaxy Evolution and Assembly (GAEA) semi-analytic model to improve our modelling of satellite galaxies. Specifically, we implement gradual stripping of hot gas, ram-pressure stripping of cold gas, and an updated algorithm to account for angular momentum exchanges between the gaseous and stellar disc components of model galaxies. Our updated model predicts quenched fractions that are in good agreement with local observational measurements for central and satellite galaxies, and their dependencies on stellar mass and halo mass. We also find consistency between model predictions and observational estimates of quenching times for satellite galaxies, H i, H2 fractions of central galaxies, and deficiencies of H i, H2, SFR of galaxies in cluster haloes. In the framework of our updated model, the dominant quenching mechanisms are hot gas stripping for low-mass satellite galaxies, and AGN feedback for massive satellite galaxies. The ram-pressure stripping of cold gas only affects the quenched fraction in massive haloes with Mh > 1013.5 M⊙, but is needed to reproduce the observed H i deficiencies.
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