arXiv subjects

Luigi Danese

Publications and source records attributed to Luigi Danese.

46 records · Page 3Linked to original sources

arXiv2001

Chemical Evolution of Elliptical Galaxies as a Constraint to Galaxy Formation Scenarios

Elliptical galaxies are the main contributors to the chemical enrichment of the intracluster and intergalactic medium; understanding how they form and evolve enables us to get important hints on the amounts of energy and processed matter that they eject into the ICM/IGM. Recent pieces of observational evidence point to a strong connection between high redshift quasars and their host galaxies. The aim of this paper is to prove that the main aspects of the chemical evolution of the spheroids can be reproduced in the framework of a model where the shining of the quasar is intimately related to the formation of the galactic nucleus. A key assumption is that the quasars shone in an inverted order with respect to the hierarchical one (i.e., stars and black holes in bigger dark halos formed before those in smaller ones) during an early episode of vigorous star formation. This scenario closely resembles the so-called `inverse wind' model invoked to explain the observed increase of the [Mg/Fe] ratio in the nuclei of ellipticals with increasing the galactic mass, the only difference being that now the time for the occurrence of a galactic wind is not determined by the energy input from supernovae, but is indeed the energy injected by the quasar which regulates the onset of the wind phase.

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arXiv2001

Dust and Nebular Emission in Star Forming Galaxies

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.

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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.

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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.

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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.

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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.

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arXiv1998

Modelling the effects of dust on galactic SEDs from the UV to the millimeter band

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.

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arXiv1997

Old Massive Ellipticals and S0 in the Hubble Deep Field Vanish from View at $z>1.3$: Possible Solutions of the Enigma

We have investigated the properties of a bright K-band selected sample of early-type galaxies in the Hubble Deep Field, as representative of the field galaxy population. This dataset is unique as for the morphological information on faint high-z sources, and for complete photometric and spectroscopic coverage. The majority of bright early-type galaxies in this field are found at redshifts $z \leq 1.3$ to share common properties with those of high-z cluster samples, as for the age and mass of the dominant stellar population -- which are found to be as old as 3-5 Gyr and as massive as $10^{11} M_\odot$ already at $z\simeq 1$. There is no evidence of a steepening of the mass function from $z$=0 to $z$=1, as inferred by some authors from analyses of optically-selected samples and favoured by hierarchical clustering models forming most of the E/S0s at $z<1$. What distinguishes this sample is a remarkable absence of objects at $z>1.3$, which would be expected as clearly detectable above the flux limits, given the aged properties of the lower redshift counterparts. So, something hide them at high redshifts. Merging could be an explanation, but it would require that already formed and old stellar systems would assemble on short timescales of 1 Gyr or less. Only a negligible fraction of the galactic mass in young stars has to be added, a rather contrived situation from the dynamical point of view. An alternative interpretation could be that a dust-polluted ISM obscures the first 3 to 4 Gyr of the evolution of these massive systems, after which a galactic wind and gas consumption makes them transparent. The presence of dust would have relevant (and testable) implications for the evaluation of the global energetics from galaxy formation and for the visibility of the early phases by current and future infrared

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arXiv1997

Thick tori around AGN: the case for extended tori and consequences for their X-ray and IR emission

Two families of models of dusty tori in AGNs (moderately thick and extended versus very thick and compact) are tested against available observations. The confrontation suggests that the former class better explains the IR broad-band spectra of both broad and narrow line AGNs, the anisotropy of the emission deduced by comparing IR properties of Seyfert 1 and 2 nuclei, the results of IR spectroscopy and those of high spatial resolution observations. There is however clear evidence for a broad distribution of optical depths. We also examine the relationship between IR and X-ray emission. The data support a view in which the matter responsible for the X-ray absorption is mostly dust free, lying inside the dust sublimation radius. The consequences of these results for the hard X-ray background as well as IR counts and background are discussed.

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arXiv1996

Dust Enshrouded AGN Models for Hyperluminous High Redshift IR Galaxies

We investigate models for the power supply and broad-band spectral energy distribution (SED) of hyperluminous IR galaxies, recently discovered at high redshifts, in terms of the emission from an active nucleus embedded in a torus-like dusty structure. We find consistent solutions in terms of a simple torus model extended several hundreds of parsecs, with $A_V$ in the equatorial plane of a few hundreds and a typical covering factor of over $50\%$. Objects as different as the prototype high-z galaxy \fd, the z=0.93 IR object \fq, \fz\ found in a high-z cooling flow, and the optically selected BAL "Cloverleaf" quasar, are all fitted by the same solution, for decreasing values of the polar angle to the line-of-sight and proper scaling of the luminosities. We suggest that such luminous high-z IR objects are heavily buried quasars surrounded by large amounts of dust with high covering factors and large optical depths. Comparison with UVX QSOs suggests that they are observed during a transient phase. Forthcoming observations in the far-IR will soon allow probing this phase and its relationship with the -- possibly concomitant -- formation of the nuclear black hole and of the host galaxy.

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