arXiv subjects

Pierluigi Monaco

Publications and source records attributed to Pierluigi Monaco.

At least 91 records · Page 5Linked to original sources

arXiv2007

Reproducing the assembly of massive galaxies within the hierarchical cosmogony

In order to gain insight into the physical mechanisms leading to the formation of stars and their assembly in galaxies, we compare the predictions of the MOdel for the Rise of GAlaxies aNd Active nuclei (MORGANA) to the properties of K- and 850 micron-selected galaxies (such as number counts, redshift distributions and luminosity functions) by combining MORGANA with the spectrophotometric model GRASIL. We find that it is possible to reproduce the K- and 850 micron-band datasets at the same time and with a standard Salpeter IMF, and ascribe this success to our improved modeling of cooling in DM halos. We then predict that massively star-forming discs are common at z~2 and dominate the star-formation rate, but most of them merge with other galaxies within ~100 Myr. Our preferred model produces an overabundance of bright galaxies at z<1; this overabundance might be connected to the build-up of the diffuse stellar component in galaxy clusters, as suggested by Monaco et al. (2006), but a naive implementation of the mechanism suggested in that paper does not produce a sufficient slow-down of the evolution of these objects. Moreover, our model over-predicts the number of 10^{10}-10^{11} M_sun galaxies at z~1; this is a common behavior of theoretical models as shown by Fontana et al. (2006). These findings show that, while the overall build-up of the stellar mass is correctly reproduced by galaxy formation models, the ``downsizing'' trend of galaxies is not fully reproduced yet. This hints to some missing feedback mechanism in order to reproduce at the same time the formation of both the massive and the small galaxies.

astro-ph↗

arXiv2006

The luminosity function of high-redshift QSOs

We measure the luminosity function of QSOs in the redshift range 3.5 < z < 5.2 for the absolute magnitude interval -21 < M_{145} < -28. Suitable criteria are defined to select faint QSOs in the GOODS fields, checking their effectiveness and completeness in detail. The confirmed sample of faint QSOs is compared with a brighter one derived from the SDSS. Using a Monte-Carlo technique we estimate the properties of the luminosity function. Our results show that models based on pure density evolution show better agreement with observation than models based on pure luminosity evolution, even if a different break magnitude with respect to z ~ 2.1 is required at 3.5 < z < 5.2. According to our modeling a faint-end slope steeper than low-redshift observations is required to reproduce the data, moreover models with a steep bright-end slope score a higher probability than models with a bright-end flattening. Determining the faint-end of the luminosity function at these redshifts provides important constraints on models of the joint evolution of galaxies and AGNs.

astro-ph↗

arXiv2006

Constraining feedback in galaxy formation: using galaxy and AGN surveys to shed light on "gastrophysics"

We present some results of the new MORGANA model for the rise of galaxies and active nuclei, and show that the improved physical motivation of the description of star formation and feedback allows to get hints on the physical processes at play. We propose that the high level of turbulence in star-forming bulges is at the base of the observed downsizing of AGNs. In this framework it is also possible to reproduce the recently obtained evidence that most low-redshift accretion is powered by relatively massive, slowly accreting black holes. Besides, we notice that many galaxy formation models (including MORGANA) fail to reproduce a basic observable, namely the number density of 10^{11} Msun galaxies at z~1, as traced by the GOODS-MUSIC sample. This points to a possibly missing ingredient in the modeling of stellar feedback.

astro-ph↗

arXiv2006

The MORGANA model for the rise of galaxies and active nuclei

We present the MOdel for the Rise of GAlaxies aNd Active nuclei (MORGANA). Starting from the merger trees of dark matter halos and a model for the evolution of substructure within the halos, the complex physics of baryons is modeled with a set of state-of-the-art models that describe the mass, metal and energy flows between the various components and phases of a galaxy. The processes of shock-heating and cooling, star formation, feedback, galactic winds and super-winds, accretion onto BHs 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 multi-phase model by Monaco (2004a). The increased level of sophistication allows to move from a phenomenological description of gas physics, based on simple scalings with the depth of the DM halo potential, toward a fully physically motivated one. 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 cutoff 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 dark matter halos are assumed to have a very low concentration, (iii) the mass function of HI 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. (ABRIDGED)

astro-ph↗

arXiv2006

Diffuse stellar component in galaxy clusters and the evolution of the most massive galaxies at z<~1

The high end of the stellar mass function of galaxies is observed to have little evolution since z~1. This represents a stringent constraint for merger--based models, aimed at explaining the evolution of the most massive galaxies in the concordance LambdaCDM cosmology. In this Letter we show that it is possible to remove the tension between the above observations and model predictions by allowing a fraction of stars to be scattered to the Diffuse Stellar Component (DSC) of galaxy clusters at each galaxy merger, as recently suggested by the analysis of N-body hydrodynamical simulations. To this purpose, we use the MORGANA model of galaxy formation in a minimal version, in which gas cooling and star formation are switched off after z=1. In this way, any predicted evolution of the galaxy stellar mass function is purely driven by mergers. We show that, even in this extreme case, the predicted degree of evolution of the high end of the stellar mass function is larger than that suggested by data. Assuming instead that a significant fraction, ~30 per cent, of stars are scattered in the DSC at each merger event, leads to a significant suppression of the predicted evolution, in better agreement with observational constraints, while providing a total amount of DSC in clusters which is consistent with recent observational determinations.

astro-ph↗

arXiv2006

The effect of stellar feedback and quasar winds on the AGN population

In order to constrain the physical processes that regulate and downsize the 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 X-ray and hard X-ray bands, to the local 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 LambdaCDM cosmogony, and that the most likely responsible for 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 need to require that quasar-triggered galactic winds self-limit the accretion onto BHs. In all cases, the predicted BH--bulge relation steepens considerably with respect to the observed one at bulge masses <10^{11} Msun; 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 for 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 sub-mm to X-rays.

astro-ph↗

arXiv2004

On the destruction of star-forming clouds

Type II supernovae (SNe), probably the most important contributors to stellar feedback in galaxy formation, explode within the very dense star-forming clouds, where the injected energy is most easily radiated away. The efficiency of type II SNe in injecting energy into the interstellar medium (ISM) and in re-heating a fraction of the original star-forming cloud is estimated with the aid of a two-phase model for the ISM of the cloud. We argue that when SNe explode the star-forming cloud has already been partially destroyed by ionizing light and winds from massive stars. SN remnants (SNRs) will first cause the collapse of most of the cloud gas into cold fragments, until the diffuse hot phase has a low enough density to make further radiative losses negligible. This is completed in ~3 Myr, with a modest energy loss of ~5 per cent of the total budget. We compute that a fraction ranging from 5 to 30 per cent of the cloud is reheated to a high temperature (from 10^5 to 10^7 K); these numbers are very uncertain, due to the very complicated nature of the problem, and to the uncertain role of thermal evaporation. Small star-forming clouds, less massive than ~10^4 Msun, will be destroyed by a single SN. In all cases, a high fraction of the energy from type II SNe (~80 per cent for large clouds, smaller but still significant for small clouds) will be available for heating the ISM.

astro-ph↗

arXiv2003

Recovering the Initial Condition of our Local Universe from NOG and PSCz Catalogues

We apply the ZTRACE algorithm to the optical NOG and infra-red PSCz galaxy catalogues to reconstruct the pattern of primordial fluctuations that have generated our local Universe. We check that the density fields traced by the two catalogues are well correlated, and consistent with a linear relation (either in $δ$ or in log(1+$δ$)) with relative bias (of NOG with respect to PSCz) b_rel = 1.1 $\pm$ 0.1. The relative bias relation is used to fill the optical zone of avoidance at |b| < 20$^\circ$ using the PSCz galaxy density field. We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber k_lim $\simeq$ 0.4 h/Mpc beyond which all information is lost. We find that the improvement due to the denser sampling of the optical catalogue is compensated by the uncertainties connected to the larger zone of avoidance. The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSCz) to be consistent with Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe.

astro-ph↗

arXiv1999

The Mass Of Black Holes in the Nuclei Of Spirals

We use rotation curve kinematics of 1000 spiral galaxies to investigate if these galaxies could host BH (Black Hole) remnants that once powered the QSO phenomenon. The rotation curves of both early and late-type spirals are used to place upper limits on the BH mass. We find that the central objects in spirals are 10-100 times less massive than those detected in ellipticals, suggesting that the contribution to the QSO phenomenon by the BH remnants hosted in these objects is negligible. The upper limits on the mass of the BHs resident in late type spirals are stringent: $M_{BH}\leq 10^{6}-10^{7} M_{\odot}$, indicating that only low luminosity activity possibly occurred in these objects.

astro-ph↗

arXiv1999

Joint Cosmological Formation of QSOs and Bulge-dominated Galaxies

Older and more recent pieces of observational evidence suggest a strong connection between QSOs and galaxies; in particular, the recently discovered correlation between black hole and galactic bulge masses suggests that QSO activity is directly connected to the formation of galactic bulges. The cosmological problem of QSO formation is analyzed in the framework of an analytical model for galaxy formation; for the first time a joint comparison with galaxy and QSO observables is performed. In this model it is assumed that the same physical variable which determines galaxy morphology is able to modulate the mass of the black hole responsible for QSO activity. Both halo spin and the occurence of a major merger are considered as candidates to this role. The predictions of the model are compared to available data for the type-dependent galaxy mass functions, the star-formation history of elliptical galaxies, the QSO luminosity function and its evolution (including the obscured objects contributing to the hard-X-ray background), the mass function of dormant black holes and the distribution of black-hole -- bulge mass ratios. A good agreement with observations is obtained if the halo spin modulates the efficiency of black-hole formation, and if the galactic halos at $z=0$ have shone in an inverted order with respect to the hierarchical one (i.e., stars and black holes in bigger galactic halos have formed before those in smaller ones). This inversion of hierarchical order for galaxy formation, which reconciles galaxy formation with QSO evolution, is consistent with many pieces of observational evidence.

astro-ph↗

arXiv1999

The Cosmological Mass Function with 1D Gravity

The cosmological mass function problem is analyzed in full detail in the case of 1D gravity, with analytical, semi-analytical and numerical techniques. The extended Press & Schechter theory is improved by detailing the relation between smoothing radius and mass of the objects. This is done by introducing in the formalism the concept of a growth curve for the objects. The predictions of the extended Press & Schechter theory are compared to large N-body simulations of flat expanding 1D universes with scale-free power spectra of primordial perturbations. The collapsed objects in the simulations are located with a clump-finding algorithm designed to find regions that have undergone orbit crossing or that are in the multi-stream regime (these are different as an effect of the finite size of the multi-stream regions). It is found that the semi-analytical mass function theory, which has no free parameters, is able to recover the properties of collapsed objects both statistically and object by object. In particular, the predictions of regions in orbit crossing are optimized by the use of Gaussian filtering, while the use of sharp k-space filtering apparently allows to reproduce the larger multi-stream regions. The mass function theory does not reproduce well the clumps found with the standard friends-of-friends algorithm; however, the performance of this algorithm has not been thoroughly tested in the 1D cosmology. Our preliminary analyses of the 3D case confirms that the techniques developed in this paper are precious in understanding the cosmological mass function problem in 3D.

astro-ph↗

arXiv1999

Mass function of dormant black holes and the evolution of the Active Galactic Nuclei

We derive the mass function of the relic black holes and compared with that of the Massive Dark Objects in galaxies. Under the assumption that accretion onto massive BH's powers the Active Galactic Nuclei, the mass function of the BH responsibile for the past activity of QSO/AGN is computed. Our results support the scenario in which the QSO phase has exclusively occurred in every proto-elliptical.

astro-ph↗

arXiv1998

Dynamics in the cosmological mass function (or, why does the Press & Schechter work?)

The Press & Schechter ``numerical recipe'' is briefly reviewed, together with the recently proposed dynamical mass function theory, in which the mass function is constructed by using the powerful Lagrangian perturbation theory. The dynamical mass function is found in good agreement with the recent N-body simulations of Governato et al. (1998), in the case of an Einstein-de Sitter Universe. The definition of collapse, the relation between mass and smoothing radius, and the definition of structure in 1D Universes are discussed. A detailed comparison of the dynamical mass function to simulations reveals that the orbit-crossed regions in the simulation are correctly reproduced, while the fragmentation of the collapsed medium into structures cannot be done in a univocal way. Finally, we try to answer the question: why the hell does the Press & Schechter work?

astro-ph↗

arXiv1998

Dormant black holes tell a story about the evolution of active galactic nuclei

In our recent paper (Salucci et al. 1998) we have investigated the mass distribution function of massive dark objects in galaxies, exploiting the available optical and radio observations. Under the assumption that massive black holes power active galactic nuclei, we have compared the mass functions of massive dark objects and black holes responsible for the observed activity. We have found that a scenario with a single short burst per active galactic nucleus is in a good agreement with the available data. Here we summarize and discuss the main points of our study.

astro-ph↗

arXiv1997

The Cosmological Mass Function

This thesis aims to review the cosmological mass function problem, both from the theoretical and the observational point of view, and to present a new mass function theory, based on realistic approximations for the dynamics of gravitational collapse. Chapter 1 gives a general introduction on gravitational dynamics in cosmological models. Chapter 2 gives a complete review of the mass function theory. Chapters 3 and 4 present the ``dynamical'' mass function theory, based on truncated Lagrangian dynamics and on the excursion set approach. Chapter 5 reviews the observational state-of-the-art and the main applications of the mass function theories described before. Finally, Chapter 6 gives conclusions and future prospects.

astro-ph↗

arXiv1997

A Lagrangian Dynamical Theory for the Mass Function of Cosmic Structures: II Statistics

The statistical tools needed to obtain a mass function from realistic collapse time estimates are presented. Collapse dynamics has been dealt with in paper I of this series by means of the powerful Lagrangian perturbation theory and the simple ellipsoidal collapse model. The basic quantity considered here is the inverse collapse time F; it is a non-linear functional of the initial potential, with a non-Gaussian distribution. In the case of sharp k-space smoothing, it is demonstrated that the fraction of collapsed mass can be determined by extending to the F process the diffusion formalism introduced by Bond et al. (1991). The problem is then reduced to a random walk with a moving absorbing barrier, and numerically solved; an accurate analytical fit, valid for small and moderate resolutions, is found. For Gaussian smoothing, the F trajectories are strongly correlated in resolution. In this case, an approximation proposed by Peacock & Heavens (1990) can be used to determine the mass functions. Gaussian smoothing is preferred, as it optimizes the performances of dynamical predictions and stabilizes the F trajectories. The relation between resolution and mass is treated at a heuristic level, and the consequences of this approximation are discussed. The resulting mass functions, compared to the classical Press & Schechter (1974) one, are shifted toward large masses (confirming the findings of Monaco 1995), and tend to give more intermediate-mass objects at the expense of small-mass objects. However, the small-mass part of the mass function, which depends on uncertain dynamics and is likely to be affected by uncertainties in the resolution--mass relation, is not considered a robust prediction of this theory.

astro-ph↗

arXiv1997

A Lagrangian Dynamical Theory for the Mass Function of Cosmic Structures: I Dynamics

A new theory for determining the mass function of cosmic structures is presented. It relies on a realistic treatment of collapse dynamics. Gravitational collapse is analyzed in the Lagrangian perturbative framework. Lagrangian perturbations provide an approximation of truncated type, i.e. small-scale structure is filtered out. The collapse time is suitably defined as the instant at which orbit crossing takes place. The convergence of the Lagrangian series in predicting the collapse time of a homogeneous ellipsoid is demonstrated; it is also shown that third-order calculations are necessary in predicting collapse. Then, the Lagrangian prediction, with a correction for quasi-spherical perturbations, can be used to determine the collapse time of a homogeneous ellipsoid in a fast and precise way. Furthermore, ellipsoidal collapse can be considered as a particular truncation of the Lagrangian series. Gaussian fields with scale-free power spectra are then considered. The Lagrangian series for the collapse time is found to converge when the collapse time is not large. In this case, ellipsoidal collapse gives a fast and accurate approximation of the collapse time; spherical collapse is found to poorly reproduce the collapse time, even in a statistical sense. Analytical fits of the distribution functions of the inverse collapse times, as predicted by the ellipsoid model and by third-order Lagrangian theory, are given. These will be necessary for a determination of the mass function, which will be given in paper II.

astro-ph↗

arXiv1995

THE LOCAL GALAXY DENSITY AND THE BULGE-TO-DISK RATIO OF DISK GALAXIES

Relying on samples of disk galaxies for which a detailed photometric bulge/disk decomposition has been provided in the literature, we examine the dependence of the bulge-to-disk luminosity ratio (B/D) on the blue absolute luminosity and on the environmental density. In our statistical analysis of various B/D data sets we pay particular attention to disentangling the role played by the galaxy morphology--galaxy density relation. Besides, we focus our attention on nearby ($z<0.01$) galaxies, for which we can provide a three-dimensional characterization of the local galaxy density. We find that the observed tendency of galaxies to have greater B/D with increasing galaxy density simply reflects the average decline of B/D towards later morphological types together with the morphology--density relation. This relation tends to give rise also to a greater proportion of bright bulges in denser regions, because the decrease of B/D towards later types is mostly due to a dimming of the bulge rather than to a brightening of the disk. But when we remove the effect induced by the morphology--density relation, we detect no clear evidence of a dependence of B/D on galaxy density. Furthermore, B/D turns out to be substantially unrelated to the blue absolute magnitude of the galaxy. We briefly discuss to what extent our results (partially) disagree with previous claims.

astro-ph↗