Fabio Fontanot

The many manifestations of downsizing: hierarchical galaxy formation models confront observations

It has been widely claimed that several lines of observational evidence point towards a ‘downsizing’ of the process of galaxy formation over cosmic time. This behaviour is sometimes termed ‘antihierarchical’, and contrasted with the ‘bottom-up’ (small objects form first) assembly of the dark matter structures in cold dark matter (CDM) models. In this paper, we address three different kinds of observational evidence that have been described as ‘downsizing’: the stellar mass assembly (i.e. more massive galaxies assemble at higher redshift with respect to low-mass ones), star formation rate (SFR) (i.e. the decline of the specific star formation rate is faster for more massive systems) and the ages of the stellar populations in local galaxies (i.e. more massive galaxies host older stellar populations). We compare a broad compilation of available data sets with the predictions of three different semi-analytic models

Star formation and mass assembly in high redshift galaxies

Aims. The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z 0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to � 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass;

The morgana model for the rise of galaxies and active nuclei

We present the Model for the Rise of Galaxies and Active Nuclei (MORGANA), a new code for the formation and evolution of galaxies and active galactic nuclei (AGNs). Starting from the merger trees of dark matter (DM) haloes and a model for the evolution of substructure within the haloes, the complex physics of baryons is modelled with a set of state-of-the-art models that describe the mass, metal and energy flows between the various components (baryonic halo, bulge, disc) and phases (cold and hot gas, stars) of a galaxy. These flows are then numerically integrated to produce predictions for the evolution of galaxies. The processes of shock-heating and cooling, star formation, feedback, galactic winds and superwinds, accretion on to black holes and AGN feedback are described by new models. In particular, the evolution of the halo gas explicitly follows the thermal and kinetic energies of the hot and cold phases, while star formation and feedback follow the results of the multiphase model recently proposed by Monaco. The increased level of sophistication of these models allows to move from a phenomenological description of gas physics, based on simple scalings with the depth of the DM halo potential, towards a fully physically motivated one. We deem that this is fully justified by the level of maturity and rough convergence reached by the latest versions of numerical and semi-analytic models of galaxy formation. The comparison of the predictions of MORGANA with a basic set of galactic data reveals from the one hand an overall rough agreement, and from the other hand highlights a number of well- or less-known problems: (i) producing the cut-off of the luminosity function requires to force the quenching of the late cooling flows by AGN feedback, (ii) the normalization of the Tully‐Fisher relation of local spirals cannot be recovered unless the DM haloes are assumed to have a very low concentration, (iii) the mass function of H I gas is not easily fitted at small masses, unless a similarly low concentration is assumed, (iv) there is an excess of small elliptical galaxies at z = 0. These discrepancies, more than the points of agreement with data, give important clues on the missing ingredients of galaxy formation.

Luminosity function and radial distribution of Milky Way satellites in a ΛCDM Universe

We study the luminosity function (LF) and the radial distribution of satellite galaxies within Milky Way (MW) sized haloes as predicted in cold dark matter based models of galaxy formation, making use of numericalN-body techniques as well as three different semi-analytic models (SAMs) galaxy formation codes. We extract merger trees from very high-resolution dissipationless simulations of four Galaxy-sized DM haloes, and use these as common input for the SAMs. We present a detailed comparison of our predictions with the observational data recently obtained on the MW satellite LF. We find that SAMs with rather standard astrophysical ingredients are able to reproduce the observed LF over six orders of magnitude in luminosity, down to magnitudes as faint as MV =− 2. We also perform a comparison with the actual observed number of satellites as a function of luminosity, by applying the selection criteria of the SDSS survey to our simulations instead of correcting the observations for incompleteness. Using this approach, we again find good agreement for both the luminosity and radial distributions of MW satellites. We investigate which physical processes in our models are responsible for shaping the predicted satellite LF, and find that tidal destruction, suppression of gas infall by a photoionizing background, and supernova feedback all make important contributions. We conclude that the number and luminosity of MW satellites can be naturally accounted for within the (� )cold dark matter paradigm, and this should no longer be considered a problem.

The evolving slope of the stellar mass function at 0.6 ≤ z < 4.5 from deep WFC3 data

We used Early Release Science (ERS) observations taken with the Wide Field Camera 3 (WFC3) in the GOODS-S field to study the galaxy stellar mass function (GSMF) at 0.6 ≤ z 2. However, we confirm that there appears to be an excess of integrated star formation with respect to the SMD at z < 2, by a factor of ∼2−3. Our comparison of the observations with theoretical predictions shows that the models forecast a greater abundance of low mass galaxies, at least up to z ∼ 3, as well as a dearth of massive galaxies at z ∼ 4 with respect to the data, and that the predicted SMD is generally overestimated at z < 2.

The luminosity function of high-redshift quasi-stellar objects. A combined analysis of GOODS and SDSS

Aims. In this work the luminosity function of QSOs is measured in the redshift range

Ages and metallicities of central and satellite galaxies: implications for galaxy formation and evolution

3.5 Methods. We have defined suitable criteria to select faint QSOs in the GOODS fields, checking their effectiveness and completeness in detail. A spectroscopic follow-up of the resulting QSO candidates was carried out. The confirmed sample of faint QSOs is compared with a brighter one derived from the SDSS. We used a Monte-Carlo technique to estimate the properties of the luminosity function, checking various parameterizations for its shape and evolution. Results. Models based on pure density evolution show better agreement with observation than do models based on pure luminosity evolution. However, a different break magnitude with respect to

Diffuse Stellar Component in Galaxy Clusters and the Evolution of the Most Massive Galaxies at z ≲ 1

z\sim 2.1

On the relative contribution of high-redshift galaxies and active galactic nuclei to reionization

is required at

A semi-analytic model comparison – gas cooling and galaxy mergers

3.5 3.5