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Luigi Danese

Publications and source records attributed to Luigi Danese.

At least 37 records · Page 2Linked to original sources
arXiv2014

A physical model for the evolving UV luminosity function of high redshift galaxies and their contribution to the cosmic reionization

[Abridged] We present a physical model for the evolution of the ultraviolet (UV) luminosity function (LF) of high-z galaxies taking into account in a self-consistent way their chemical evolution and the associated evolution of dust extinction. The model yields good fits of the UV and Lyman-alpha LFs at z>~2. The weak evolution of both LFs between z=2 and z=6 is explained as the combined effect of the negative evolution of the halo mass function, of the increase with redshift of the star formation efficiency, and of dust extinction. The slope of the faint end of the UV LF is found to steepen with increasing redshift, implying that low luminosity galaxies increasingly dominate the contribution to the UV background at higher and higher redshifts. The observed range of UV luminosities at high-z implies a minimum halo mass capable of hosting active star formation M_crit <~ 10^9.8 M_odot, consistent with the constraints from hydrodynamical simulations. From fits of Lyman-alpha LFs plus data on the luminosity dependence of extinction and from the measured ratios of non-ionizing UV to Lyman-continuum flux density for samples of z=~3 Lyman break galaxies and Lyman-alpha emitters, we derive a simple relationship between the escape fraction of ionizing photons and the star formation rate, impling larger escape fraction for less massive galaxies. Galaxies already represented in the UV LF (M_UV <~ -18) can keep the universe fully ionized up to z=~6, consistent with (uncertain) data pointing to a rapid drop of the ionization degree above z~6. On the other side, the electron scattering optical depth, tau_es, inferred from CMB experiments favor an ionization degree close to unity up to z=~9-10. Consistency with CMB data can be achieved if M_crit =~ 10^8.5 M_odot, implying that the UV LFs extend to M_UV =~ -13, although the corresponding tau_es is still on the low side of CMB-based estimates.

astro-ph.CO↗
arXiv2013

Cosmic dichotomy in the hosts of rapidly star-forming systems at low and high redshifts

This paper presents a compilation of clustering results taken from the literature for galaxies with highly enhanced (SFR [30-10^3] Msun/yr) star formation activity observed in the redshift range z=[0-3]. We show that, irrespective of the selection technique and only very mildly depending on the star forming rate, the clustering lengths of these objects present a sharp increase of about a factor 3 between z~1 and z~2, going from values of ~5 Mpc to about 15 Mpc and higher. This behaviour is reflected in the trend of the masses of the dark matter hosts of star-forming galaxies which increase from ~10^11.5 Msun to ~10^13.5 Msun between z~1 and z~2. Our analysis shows that galaxies which actively form stars at high redshifts are not the same population of sources we observe in the more local universe. In fact, vigorous star formation in the early universe is hosted by very massive structures, while for z~1 a comparable activity is encountered in much smaller systems, consistent with the down-sizing scenario. The available clustering data can hardly be reconciled with merging as the main trigger for intense star formation activity at high redshifts. We further argue that, after a characteristic time-scale of ~1 Gyr, massive star-forming galaxies at z>~2 evolve into z<~1.5 passive galaxies with large (Mstellar=[10^11 - 10^12] Msun) stellar masses.

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arXiv2013

Black-hole mass estimates for a homogeneous sample of bright flat-spectrum radio quasars

We have selected a complete sample of flat-spectrum radio quasars (FSRQs) from the WMAP 7-yr catalog within the SDSS area, all with measured redshift, and have compared the black hole mass estimates based on fitting a standard accretion disk model to the `blue bump' with those obtained from the commonly used single epoch virial method. The sample comprises 79 objects with a flux density limit of 1 Jy at 23 GHz, 54 of which (68%) have a clearly detected `blue bump'. Thirty-four of the latter have, in the literature, black hole mass estimates obtained with the virial method. The mass estimates obtained from the two methods are well correlated. If the calibration factor of the virial relation is set to $f=4.5$, well within the range of recent estimates, the mean logarithmic ratio of the two mass estimates is equal to zero with a dispersion close to the estimated uncertainty of the virial method. The fact that the two independent methods agree so closely in spite of the potentially large uncertainties associated with each lends strong support to both of them. The distribution of black-hole masses for the 54 FSRQs in our sample with a well detected blue bump has a median value of $7.4\times 10^{8}\,M_\odot$. It declines at the low mass end, consistent with other indications that radio loud AGNs are generally associated with the most massive black holes, although the decline may be, at least partly, due to the source selection. The distribution drops above $\log(M_\bullet/M_\odot) = 9.4$, implying that ultra-massive black holes associated with FSRQs must be rare.

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arXiv2013

The Star Formation History of Redshift z~2 Galaxies: The Role of The Infrared Prior

We build a sample of 298 spectroscopically-confirmed galaxies at redshift z~2, selected in the z-band from the GOODS-MUSIC catalog. By exploiting the rest frame 8 um luminosity as a proxy of the star formation rate (SFR) we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the galaxy physical parameters. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable RV . Then we exploit such a new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 1000 solar mass per year, the masses from one billion to 400 billion solar masses, while the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age easurements of highly attenuated objects indicate that dust must form within a few tens of Myr and be copious already at ~100 Myr. In addition, we find that low luminous galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known 'downsizing' scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed mass-to-light ratios.

astro-ph.CO↗
arXiv2013

A hybrid model for the evolution of galaxies and Active Galactic Nuclei in the infrared

[Abridged] We present a comprehensive investigation of the cosmological evolution of the luminosity function (LF) of galaxies and active galactic nuclei (AGN) in the infrared (IR). Based on the observed dichotomy in the ages of stellar populations of early-type galaxies on one side and late-type galaxies on the other, the model interprets the epoch-dependent LFs at z \geq 1.5 using a physical model for the evolution of proto-spheroidal galaxies and of the associated AGNs, while IR galaxies at z<1.5 are interpreted as being mostly late-type 'cold' (normal) and 'warm' (starburst) galaxies. As for proto-spheroids, in addition to the epoch-dependent LFs of stellar and AGN components separately, we have worked out the evolving LFs of these objects as a whole (stellar plus AGN component). The model provides a physical explanation for the observed positive evolution of both galaxies and AGNs up to z \simeq 2.5 and for the negative evolution at higher redshifts, for the sharp transition from Euclidean to extremely steep counts at (sub-)mm wavelengths, as well as the (sub-)mm counts of strongly lensed galaxies, that are hard to account for by alternative, physical or phenomenological, approaches. The evolution of late-type galaxies and of z<1.5 AGNs is described using a parametric phenomenological approach. The modeled AGN contributions to the counts and to the cosmic infrared background (CIB) are always subdominant with maximal at mid-IR wavelengths. The model provides a good fit to the multi-wavelength (from the mid-IR to millimeter waves) data on LFs at different redshifts and on number counts (both global and per redshift slices). A prediction of the present model is a systematic variation with wavelength of the populations dominating the counts and the contributions to the CIB intensity. The implied specific trend for cross-wavelength CIB power spectra is found to be in good agreement with the data.

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arXiv2012

The HI Content of Local Late-Type Galaxies

We present a solid relationship between the neutral hydrogen (HI) disk mass and the stellar disk mass of late-type galaxies in the local universe. This relationship is derived by comparing the stellar disk mass function from the Sloan Digital Sky Survey and the HI mass function from the HI Parkes All Sky Survey (HIPASS). We find that the HI mass in late-type galaxies tightly correlates with the stellar mass over three orders of magnitude in stellar disk mass. We cross-check our result with that obtained from a sample of HIPASS objects for which the stellar mass has been obtained by inner kinematics. In addition, we derive the HI versus halo mass relationship and the dependence of all the baryonic components in spirals on the host halo mass. These relationships bear the imprint of the processes ruling galaxy formation, and highlight the inefficiency of galaxies both in forming stars and in retaining their pristine HI gas.

astro-ph.CO↗
arXiv2010

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs.

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arXiv2007

Exploring Supermassive Black Hole Growth with ALMA

Massive tori with $\approx 10^{8-9}M_{\odot}$ are predicted to extend on $\sim $100 pc scale around the centre of elliptical galaxy progenitors by a model of a supermassive black hole (SMBH) growth coeval to the spheroidal population of the host galaxy. Direct detection of such massive tori would cast light on a key physical condition that allows the rapid growth of SMBHs and the appearance of QSOs at high redshift. For this reason, we examine the detectability of such structures at substantial redshift with the Atacama Large Millimeter Array (ALMA). We propose that submillimeter galaxies (SMGs) are the best targets to test our predictions. In order to assess the observational feasibility, we estimate the expected number counts of SMGs with massive tori and check the detectability with the ALMA instrument, the unique facility which can resolve the central region of high redshift objects. Our work shows that ALMA will be able to resolve and detect high-$J$ ($J >$ 4) CO emissions from $\sim$100 pc scale extended massive tori up to $z\approx2$. Observations of lensed SMGs will yield excellent spatial resolution, allowing even to resolve their massive tori at higher redshift. We discuss further the detectability of the HCN molecule, as a better tracer of the high density gas expected in such tori. The final goal of these kind of observations is to pinpoint possible physical mechanisms that storage in the very central galactic regions very large amount gas on timescale of several 10$^{8}$ yr.

astro-ph↗
arXiv2005

A Physical Model for the joint evolution of high-z QSOs and Spheroids

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.

astro-ph↗
arXiv2004

Observational tests of the evolution of spheroidal galaxies

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]

astro-ph↗
arXiv2004

Observational tests of the evolution of spheroidal galaxies and predictions for SIRTF/Spitzer cosmological surveys

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]

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arXiv2004

Observational tests of the galaxy formation process

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.

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arXiv2003

A Physical Model for the Co-evolution of QSOs and of their Spheroidal Hosts

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.

astro-ph↗
arXiv2002

The Fundamental Plane of Ellipticals: I. The Dark Matter Connection

We show that the small scatter around the Fundamental Plane (FP) of massive elliptical galaxies can be used to derive important properties of their dark and luminous matter. The central velocity dispersion sigma_0, appearing in (e.g.) the Fundamental Plane, is linked to photometric, dynamical and geometrical properties of (luminous and dark) matter. We find that, inside the effective radius R_e, the matter traced by the light must largely dominate over the dark matter (DM), in order to keep the ellipticals close enough to the FP. This recalls analogous findings for spiral galaxies. In particular we also find that cuspy DM distributions, as predicted by numerical simulations in Lambda CDM cosmology, are unable to explain the very existence of the FP; in fact, according to this theory, the structural properties of dark and luminous matter are so interwoven that a curved surface is predicted in the log-space (sigma_0, R_e, L), rather than a plane. In order to agree with the FP, CDM halos must have concentrations parameters in the range of 5-9 (i.e. values significantly lower than the current predictions). Assuming a more heuristic approach and allowing for cored DM halos, we find that the small intrinsic scatter of the FP yields to i) an average value for the dark-to-light-traced mass ratio inside the length-scale of light R_e of about 0.3, ii) a mass-to-light ratio of the matter traced by the light increasing with spheroid luminosity as L^(0.2) in Gunn-r band, with a value of 5.3 at L = 2.7 x 10^{10} L_{sol}.

astro-ph↗
arXiv2002

Millimeter-band Surveys of Extragalactic 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.

astro-ph↗
arXiv2002

Chemical evolution in a model for the joint formation of quasars and spheroids

Direct and indirect pieces of observational evidence point to a strong connection between high-redshift quasars and their host galaxies. In the framework of a model where the shining of the quasar is the episode that stops the formation of the galactic spheroid inside a virialized halo, it has been proven possible to explain the submillimetre source counts together with their related statistics and the local luminosity function of spheroidal galaxies. The time delay between the virialization and the quasar manifestation required to fit the counts is short and incresing with decresing the host galaxy mass. In this paper we compute the detailed chemical evolution of gas and stars inside virialized haloes in the framework of the same model, taking into account the combined effects of cooling and stellar feedback. Under the assumption of negligible angular momentum, we are able to reproduce the main observed chemical properties of local ellipticals. In particular, by using the same duration of the bursts which are required in order to fit the submillimetre source counts, we recover the observed increase of the Mg/Fe ratio with galactic mass. Since for the most massive objects the assumed duration of the burst is Tburst < 0.6 Gyr, we end up with a picture for elliptical galaxy formation in which massive spheroids complete their assembly at early times, thus resembling a monolithic collapse, whereas smaller galaxies are allowed for a more prolonged star formation, thus allowing for a more complicated evolutionary history.

astro-ph↗
arXiv2001

Spheroidal Galaxies/QSOs Connection

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.

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