arXiv subjects
Publications and source records attributed to Gian Luigi Granato.
We point out that in Granato & Danese 1994 and Granato et al. 1997 we predicted maximum observable sizes for the putative torus in NGC1068 of 10-20 pc, not "hundreds of parsecs" as stated by M. Elitzur in astro-ph/0512025.
We summarize our physical model for the early co-evolution of spheroidal galaxies and of active nuclei at their centers. Our predictions are in excellent agreement with a number of observables which proved to be extremely challenging for all the current semi-analytic models, including the sub-mm counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies. Also, the black hole mass function and the relationship between the black hole mass and the velocity dispersion in the galaxy are nicely reproduced. The mild AGN activity revealed by X-ray observations of SCUBA sources is in keeping with our scenario, and testify the build up of SMBH triggered by intense star formation.
Granato et al (2004) have elaborated a physically grounded model exploiting the mutual feedback between star-forming spheroidal galaxies and the active nuclei growing in their cores to overcome, in the framework of the hierarchical clustering scenario for galaxy formation, one of the main challenges facing such scenario, the fact that massive spheroidal galaxies appear to have formed much earlier and faster than predicted by previous semi-analytical models. After having assessed the values of the two parameters that control the effect of the complex radiative transfer processes on the time-dependent SEDs we have compared the model predictions with a variety of IR to mm data. Our results support a rather strict continuity between objects where stars formed and evolved massive early-type galaxies, indicating that large spheroidal galaxies formed most of their stars when they were already assembled as single objects. The model is successful in reproducing the observed z distribution of K\le20 galaxies at z>1, in contrast with both the classical monolithic and the semi-analytic models, the ratio of star-forming to passively evolving spheroids and the counts and z distributions of EROs. The model also favourably compares with the ISOCAM 6.7 mu counts, with the corresponding z distribution, and with IRAC counts, which probe primarily the passive evolution phase, and with the submm SCUBA and MAMBO data, probing the active star-formation phase. The observed fraction of 24mu selected sources with no detectable emission in either the 8mu or R band nicely corresponds to the predicted surface density of star-forming spheroids with 8mu fluxes below the detection limit. Predictions for the z distributions of 24mu sources detected by MIPS surveys are pointed out. [Abridged]
We estimate the contribution of AGNs and of their host galaxies to the infrared background. We use the luminosity function and evolution of AGNs recently determined by the hard X-ray surveys, and new Spectral Energy Distributions connecting the X-ray and the infrared emission, divided in intervals of absorption. These two ingredients allow us to determine the contribution of AGNs to the infrared background by using mostly observed quantities, with only minor assumptions. We obtain that AGN emission contributes little to the infrared background ($<$5% over most of the infrared bands), implying that the latter is dominated by star formation. However, AGN host galaxies may contribute significantly to the infrared background, and more specifically 10--20% in the 1--20$μ$m range and $\sim$5% at $λ<60μm$. We also give the contribution of AGNs and of their host galaxies to the source number counts in various infrared bands, focusing on those which will be observed with Spitzer. We also report a significant discrepancy between the expected contribution of AGN hosts to the submm background and bright submm number counts with the observational constraints. We discuss the causes and implications of this discrepancy and the possible effects on the Spitzer far-IR bands.
We determined C, N and alpha-element relative abundances in the gas surrounding six QSOs at an average redshift of < z > ~ 2.4, by studying six narrow associated absorption systems in UVES high-resolution spectra. We found five systems with a metallicity (measured by C/H) consistent or above the solar value. The ionization structure observed in the associated systems is clearly different from that of the intervening ones, indicating that the associated systems are influenced by the strong UV flux from the QSO. There is a possible correlation (anticorrelation) between [N/C] ([Si/C]) and [C/H] of the studied associated systems, and [N/C] >= 0 when [C/H] >= 0. We have compared these observational results with the predictions of a model simulating the joint evolution of QSOs and their spheroidal hosts. The agreement turns out to be very good, in particular, the case envisaging massive haloes and high star-formation rates recovers both the correlation between [N/C] and [C/H] and the anticorrelation for [Si/C] vs. [C/H]. Narrow associated absorption systems prove to be powerful tracers of the chemical abundances in gas belonging to high redshift spheroidal galaxies. The outflow of this same gas, triggered by the QSO feedback, is probably going to contribute to the early enrichment of the surrounding intergalactic medium. A larger statistics, possibly increasing the number of ionisation stages, chemical elements and the redshift range, would allow us to put firm constraints on detailed chemical evolution models of galaxies at high redshifts.
Granato et al(2004) have elaborated a physically grounded model exploiting the mutual feedback between star-forming spheroidal galaxies and the active nuclei growing in their cores to overcome, within the hierarchical clustering scenario for galaxy formation, one of the main challenges facing such scenario, the fact that massive spheroidal galaxies appear to have formed earlier and faster than predicted by previous models. Adopting the choice by Granato et al for the parameters governing the history of the SF,of chemical abundances and of the gas and dust content of galaxies, we are left with only two parameters affecting the time and mass dependent SED of spheroidal galaxies. After complementing the model with a simple description of evolutionary properties of starburst, normal late-type galaxies and AGNs we have successfully compared the model with a broad variety of observational data, deep K-band, ISO, IRAS, SCUBA, radio counts, the corresponding redshift distributions, the IR background spectrum, and also with data for EROs. We also present detailed predictions for the GOODS and SWIRE surveys with the Spitzer Space Telescope. We find that the GOODS deep survey at 24$μ$m and the SWIRE surveys at 70 and 160$μ$m are likely to be severely confusion limited. The GOODS surveys in the IRAC channels are expected to resolve most of the background, to explore the full passive evolution phase of spheroidal galaxies and most of their active star-forming phase, detecting galaxies up to z\simeq 4. A substantial number of high z star-forming spheroidal galaxies should also be detected by the 24\mum SWIRE and GOODS surveys, while the 70 and 160\mum will be particularly useful to study the evolution of such galaxies in the range 1 \lsim z \lsim 2.[abridged]
The mutual feedback between star formation and nuclear activity in large spheroidal galaxies may be a key ingredient to overcome several difficulties plaguing current semi-analytic models for galaxy formation. We discuss some observational implications of the model by Granato et al. (2003) for the co-evolution of galaxies and active nuclei at their centers and stress the potential of the forthcoming surveys of the Sunyaev-Zeldovich effect on arcminute scales, down to $μ$K levels, to investigate the early galaxy formation phases, difficult to access by other means.
We present a physically motivated model for the early co-evolution of massive spheroidal galaxies and active nuclei at their centers. Within dark matter halos, forming at the rate predicted by the canonical hierarchical clustering scenario, the gas evolution is controlled by gravity, radiative cooling, and heating by feedback from supernovae and from the growing active nucleus. Supernova heating is increasingly effective with decreasing binding energy in slowing down the star formation and in driving gas outflows. The more massive proto-galaxies virializing at earlier times are thus the sites of the faster star-formation. The correspondingly higher radiation drag fastens the angular momentum loss by the gas, resulting in a larger accretion rate onto the central black-hole. In turn, the kinetic energy carried by outflows driven by active nuclei can unbind the residual gas, thus halting both the star formation and the black-hole growth, in a time again shorter for larger halos. For the most massive galaxies the gas unbinding time is short enough for the bulk of the star-formation to be completed before type Ia supernovae can substantially increase the $Fe$ abundance of the interstellar medium, thus accounting for the $α$-enhancement seen in the largest galaxies. The feedback from supernovae and from the active nucleus also determines the relationship between the black-hole mass and the mass, or the velocity dispersion, of the host galaxy, as well as the black-hole mass function. These and other model predictions are in excellent agreement with observations for a number of observables which proved to be extremely challenging for all the current semi-analytic models, including the sub-mm counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies.
We revisit the nature of the FIR/Radio correlation by means of the most recent models for star forming galaxies. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). As for the radio emission, we revisit the simple model of Condon & Yin (1990). We find that a tightFIR/Radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electrons cooling time is shorter than the fading time of the supernova rate. Observations indicate that both these conditions are met in star forming galaxies. However since the radio non thermal emission is delayed, deviations are expected both in the early phases of a starburst, when the radio thermal component dominates, and in the post-starburst phase, when the bulk of the NT component originates from less massive stars. This delay allows the analysis of obscured starbursts with a time resolution of a few tens of Myrs, unreachable with other star formation indicators. We suggest to complement the analysis of the deviations from the FIR/Radio correlation with the radio slope to obtain characteristic parameters of the burst. The analysis of a sample of compact ULIRGs shows that they are intense but transient starbursts, to which one should not apply usual SF indicators devised for constant SF rates. We also discuss the possibility of using the q- radio slope diagram to asses the presence of obscured AGN. A firm prediction of the models is an apparent radio excess during the post-starburst phase, which seems to be typical of a class of star forming galaxies in rich cluster cores. We discuss how deviations from the correlation, due to the evolutionary status of the starburst, affect the technique of photometric redshift determination widely used for high-z sources.
Surveys at mm wavelengths emphasize rare classes of extragalactic radio sources characterized by spectra keeping flat or inverted up to high frequencies (such as blazars, GPS sources, advection dominated sources, or even gamma-ray burst afterglows), which are are difficult to single out at lower frequencies where the counts are dominated by far more numerous populations. Such surveys may lead to the discovery of populations with extreme properties, such as sources of the general GPS or blazar type but peaking at mm wavelengths, whose existence is hinted by currently available data. At relatively lower flux levels mm counts are dominated by high-redshift dusty galaxies, such as those detected by SCUBA and MAMBO surveys. These data have profound implications for our understanding of the formation and early evolution of galaxies. High sensitivity surveys at cm/mm wavelengths may also detect galaxy-scale Sunyaev-Zeldovich effects due to gas heated by central active nuclei.
In view of the extensive evidence of a tight inter-relationship between spheroidal galaxies (and galactic bulges) and massive black holes hosted at their centers, a consistent model must deal jointly with the evolution of the two components. We describe one viable model, which successfully accounts for the local luminosity function of spheroidal galaxies, their photometric and chemical properties, deep galaxy counts in different wavebands, including those in the (sub)-mm region which proved to be critical for current semi-analytic models stemming from the standard hierarchical clustering picture, clustering properties of SCUBA galaxies, of EROs, and of LBGs, as well as for the local mass function of massive black holes and for quasar evolution. Predictions that can be tested by surveys carried out by SIRTF are presented.
We analyse very deep X-ray and mid-IR surveys in common areas of the Lockman Hole and the HDF North to study the sources of the X-ray background (XRB) and to test the standard obscured accretion paradigm. We detect with ISO a rich population of X-ray luminous sources with red optical colours, including a fraction identified with Extremely Red Objects (R-K > 5) and galaxies with SEDs typical of normal massive ellipticals or spirals at z ~ 1. The high 0.5-10 keV X-ray luminosities of these objects (1E43-1E45 erg/s) indicate that the ultimate energy source is gravitational accretion, while the X-ray to IR flux ratios and the X-ray spectral hardness show evidence of photoelectric absorption at low X-ray energies. An important hint on the physics comes from the mid-IR data at 6.7 and 15 um, well reproduced by model spectra of completely obscured quasars under standard assumptions and l.o.s. optical depths tau ~ 30-40. Other predictions of the standard XRB picture, like the distributions of intrinsic bolometric luminosities and the relative fractions of type-I and -II objects (1:3), are also consistent with our results. Obscured gravitational accretion is then confirmed as being responsible for the bulk of the X-ray background, since we detect in the IR the down-graded energy photoelectrically absorbed in X-rays: 63% of the faint 5-10 keV XMM sources are detected in the mid-IR by Fadda et al. (2001). However, although as much as 90% of the X-ray energy production could be converted to IR photons, no more than 20% of the Cosmic IR Background can be attributed to X-ray loud AGNs.
We present our model to interpret the SED of galaxies. The model for the UV to sub-mm SED is already well established (Silva et al 1998). We remind here its main features and show some applications. Recently we have extended the model to the radio range (Bressan et al 2001), and we have started to include the X-ray emission from the stellar component.
Star forming galaxies exhibit a variety of physical conditions, from quiescent normal spirals to the most powerful dusty starbursts. In order to study these complex systems, we need a suitable tool to analyze the information coming from observations at all wavelengths. We present a new spectro-photometric model which considers in a consistent way starlight as reprocessed by gas and dust. We discuss preliminary results to interpret some observed properties of VLIRGs.
We summarize recent advances in the determination of the cosmic history of star formation and other properties of high-z galaxies, and the relevance of this information in our understanding of the formation of structures. We emphasize the importance of dust reprocessing in the high--z universe, as demonstrated in particular by IR and sub-mm data. This demand a panchromatic approach to observations and suitable modelling tools. We spend also some words on expectations from future instruments.
We present detailed calculations of the magnification distribution, including both weak and strong lensing, using very recent solutions of the Dyer-Roeder (1973) equation for light propagation in a inhomogeneous universe with a cosmological constant and up-to-date models for the evolving cosmological distribution of dark matter halos. We address in particular the effect of a non-zero cosmological constant, of different density profiles of lenses, and of finite sizes of lensed sources. We show that, if dark matter fluctuations are normalized to the local cluster abundance, in the presence of a cosmological constant the optical depth for lensing {\em decreases} compared to the case of an Einstein-de Sitter universe, because halos in the relevant mass range are less abundant over a large redshift interval. We also discuss the differences in the magnification probability distributions produced by Navarro, Frenk & White (NFW) and by Singular Isothermal Sphere (SIS) density profiles of lenses. We find that the NFW lens is more efficient for moderate magnifications ($2\lsim A\lsim 4$), and less efficient for larger magnifications. Moreover, we discuss quantitatively the maximum magnification, $A_{\rm max}$, that can be achieved in the case of extended sources (galaxies) with realistic luminosity profiles, taking into account the possible ellipticity of the lens potential. Finally, we apply our results to a class of sources following the luminosity evolution typical for a unified scheme of QSO formation. We find that the lensed source counts at $850 μ$m can be larger than the unlensed ones by several orders of magnitude at flux densities $\gta100 $mJy.
I review recent advances in the determination of the cosmic history of star formation, and its relevance in our understanding of the formation of structures. I emphasize the importance of dust reprocessing in the high--z universe, as demonstrated in particular by IR and sub-mm data. This demand a panchromatic approach to observations and suitable modelling tools. I summarize the basic requirements for these models and to what extent they are satisfied by models published so far.
We present models of photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included with particular care. A chemical evolution code follows the star formation rate, the gas fraction and the metallicity, basic ingredients for the stellar population synthesis. The latter is performed with a grid of integrated spectra of simple stellar populations (SSP) of different ages and metallicities, in which the effects of dusty envelopes around asymptotic giant branch (AGB) stars are included. The residual fraction of gas in the galaxy is divided into two phases: the star forming molecular clouds and the cirrus. The relative amount is a model parameter. The molecular gas is sub--divided into clouds of given mass and radius: it is supposed that each SSP is born within the cloud and progressively escapes it. The emitted spectrum of the star forming molecular clouds is computed with a radiative transfer code. The cirrus emission is derived by describing the galaxy as an axially symmetric system, in which the local dust emissivity is consistently calculated as a function of the local field intensity due to the stellar component. Effects of very small grains, subject to temperature fluctuations, as well as PAHs are included. The model is compared and calibrated with available data of normal and starburst galaxies in the local universe, in particular new broad--band and spectroscopic ISO observations. It will be a powerful tool to investigate the star formation, the IMF, supernovae rate in nearby starbursts and normal galaxies, as well as to predict the evolution of luminosity functions of different types of galaxies at wavelengths covering four decades.