Polarization fluctuations due to extragalactic sources

We have derived the relationship between polarization and intensity fluctuations due to point sources. In the case of a Poisson distribution of a population with uniform evolution properties and constant polarization degree, polarization fluctuations are simply equal to intensity fluctuations times the average polarization degree. Conservative estimates of the polarization degree of the classes of extragalactic sources contributing to fluctuations in the frequency ranges covered by the forthcoming space missions MAP and Planck Surveyor indicate that extragalactic sources will not be a strong limiting factor to measurements of the polarization of the Cosmic Microwave Background.Comment: 15 pages LaTeX file, 3 postscript figures. Uses elsart.sty and elsart.cls Accepted for publication in New Astronom

Joint Formation of QSOs and Spheroids: QSOs as clocks of star formation in Spheroids

Direct and indirect observational evidence leads to the conclusion that high redshift QSOs did shine in the core of early type proto-galaxies during their main episode of star formation. Exploting this fact, we derive the rate of formation of this kind of stellar systems at high redshift by using the QSO Luminosity Function. The elemental proportions in elliptical galaxies, the descendents of the QSO hosts, suggest that the star formation was more rapid in more massive objects. We show that this is expected to occur in Dark Matter haloes, when the processes of cooling and heating is considered. This is also confirmed by comparing the observed sub-mm counts to those derived by coupling the formation rate and the star formation rate of the spheroidal galaxies with a detailed model for their SED evolution. In this scenario SCUBA galaxies and Lyman Break Galaxies are early type proto-galaxies forming the bulk of their stars before the onset of QSO activity.Comment: 13 pages, 8 figures, accepted by MNRAS, major revision of the formalis

Super-massive Black Hole Demography: the Match between the Local and Accreted Mass Functions

We have performed a detailed analysis of the local super-massive black-hole (SMBH) mass function based on both kinematic and photometric data and derived an accurate analytical fit in the range 10^6 <= (M_BH/M_sun) <= 5*10^9. We find a total SMBH mass density of (4.2+/-1.1)*10^5 M_sun/Mpc^3, about 25% of which is contributed by SMBHs residing in bulges of late type galaxies. Exploiting up-to-date luminosity functions of hard X-ray and optically selected AGNs, we have studied the accretion history of the SMBH population. If most of the accretion happens at constant \dot{M_BH}/M_BH the local SMBH mass function is fully accounted for by mass accreted by X-ray selected AGNs, with bolometric corrections indicated by current observations and a standard mass-to-light conversion efficiency \epsilon ~10%. The analysis of the accretion history highlights that the most massive BHs accreted their mass faster and at higher redshifts (z>1.5), while the lower mass BHs responsible for most of the hard X-ray background have mostly grown at z<1.5. The accreted mass function matches the local SMBH mass function if \epsilon ~0.09(+0.04,-0.03) and the Eddington ratio \lambda=L/L_Edd \~0.3(+0.3,-0.1) (68% confidence errors). The visibility time, during which AGNs are luminous enough to be detected by the currently available X-ray surveys, ranges from ~0.1 Gyr for present day BH masses M_BH(z=0) ~10^6 M_sun to ~0.3 Gyr for M_BH(z=0) >= 10^9 M_sun. The mass accreted during luminous phases is >= 25-30% even if we assume extreme values of \epsilon (\epsilon \~0.3-0.4). An unlikely fine tuning of the parameters would be required to account for the local SMBH mass function accomodating a dominant contribution from 'dark' BH growth (due, e.g., to BH coalescence).Comment: 12 pages, 14 figures, accepted for publication in MNRAS, minor changes following referee's comment

A Model for the Spectral Energy Distribution of the Ultraluminous Galaxy IRAS F10214+4724

If indeed early type galaxies used up most of their gas to form stars in a time short compared to their collapse time and if a roughly constant fraction of metals is locked up in dust grains, these galaxies may easily become opaque to starlight and emit most of their luminosity in the far-IR. The corresponding spectral energy distribution matches remarkably well the observed continuum spectrum of the ultraluminous galaxy IRAS F$10214+4724$ from UV to sub-mm wavelengths, i.e. over almost four decades in frequency, for a galactic age \lsim 1\,Gyr. The bolometric luminosity in this model is \simeq 2.7\times 10^{14}\Lsol ($H_0 =50\,\hbox{km}\,\hbox{s}^{-1} \,\hbox{Mpc}^{-1}$, $\Omega =1$), i.e. somewhat lower than implied by previous models. In the present framework, the bolometric luminosity of the galaxy is expected to decrease by a factor \gsim 30 during the subsequent evolution.Comment: TEX, 6 pages, 3 figures upon reques

Simulations of Galactic Cosmic Rays Impacts on the Herschel/PACS Photoconductor Arrays with Geant4 Code

We present results of simulations performed with the Geant4 software code of the effects of Galactic Cosmic Ray impacts on the photoconductor arrays of the PACS instrument. This instrument is part of the ESA-Herschel payload, which will be launched in late 2007 and will operate at the Lagrangian L2 point of the Sun-Earth system. Both the Satellite plus the cryostat (the shield) and the detector act as source of secondary events, affecting the detector performance. Secondary event rates originated within the detector and from the shield are of comparable intensity. The impacts deposit energy on each photoconductor pixel but do not affect the behaviour of nearby pixels. These latter are hit with a probability always lower than 7%. The energy deposited produces a spike which can be hundreds times larger than the noise. We then compare our simulations with proton irradiation tests carried out for one of the detector modules and follow the detector behaviour under 'real' conditions.Comment: paper submitted to Experimental Astronomy in March 200

Extragalactic Source Counts and Contributions to the Anisotropies of the Cosmic Microwave Background. Predictions for the Planck Surveyor mission

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their spatial power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA) mission. The contribution to fluctuations due to clustering of both radio and far--IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be ``clean'': at high galactic latitude (|b|>20), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, removal of contaminating signals is eased by the substantial difference between their power spectrum and that of primordial fluctuations.Comment: 10 pages, Latex, mn.sty, 8 figures included, MNRAS, in the press. Minor changes in the text. Sections 3.1 and 3.2 have been expanded. Source counts in Table 2 have been slightly changed. Figure 1,2,7 and 8 have been replaced by new version

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

At variance with most semi-analytic models, in the Anti-hierarchical Baryon Collapse scenario (Granato et al. 2001, 2004) the main driver of the galaxy formation and evolution is not the merging sequence but are baryon processes. This approach emphasizes, still in the framework of the hierarchical clustering paradigm for dark matter halos, feedback processes from supernova explosions and from active nuclei, that tie together star formation in spheroidal galaxies and the growth of black holes at their centers. We review some recent results showing the remarkably successful predictive power of this scenario, which allows us to account for the evolution with cosmic time of a broad variety of properties of galaxies and active nuclei, which proved to be very challenging for competing models.Comment: Invited talk at the Specola Vaticana Workshop on "AGN and Galaxy Evolution", Castel Gandolfo, 3-6 October 2005, 10 pages, 2 figure

From First Galaxies to QSOs: feeding the baby monsters

We present a physical model for the coevolution of massive spheroidal galaxies and active nuclei at their centers. Supernova heating is increasingly effective in slowing down the star formation and in driving gas outflows in smaller and smaller dark matter halos. Thus the more massive protogalaxies virializing at early times are the sites of faster star formation. The correspondingly higher radiation drag causes a faster angular momentum loss by the gas and induces a larger accretion rate onto the central black hole. In turn, the kinetic energy of the outflows powered by the active nuclei can unbind the residual gas in a time shorter for larger halos. The model accounts for a broad variety of dynamical, photometric and metallicity properties of early-type galaxies, for the M_BH -- \sigma relation and for the local supermassive black-hole mass function.Comment: 6 pages, contributed paper to Proceedings of the Conference on "Growing Black Holes" held in Garching, Germany, on June 21-25, 2004, edited by A. Merloni, S. Nayakshin and R. Sunyaev, Springer-Verlag series of "ESO Astrophysics Symposia

Correlated Component Analysis for diffuse component separation with error estimation on simulated Planck polarization data

We present a data analysis pipeline for CMB polarization experiments, running from multi-frequency maps to the power spectra. We focus mainly on component separation and, for the first time, we work out the covariance matrix accounting for errors associated to the separation itself. This allows us to propagate such errors and evaluate their contributions to the uncertainties on the final products.The pipeline is optimized for intermediate and small scales, but could be easily extended to lower multipoles. We exploit realistic simulations of the sky, tailored for the Planck mission. The component separation is achieved by exploiting the Correlated Component Analysis in the harmonic domain, that we demonstrate to be superior to the real-space application (Bonaldi et al. 2006). We present two techniques to estimate the uncertainties on the spectral parameters of the separated components. The component separation errors are then propagated by means of Monte Carlo simulations to obtain the corresponding contributions to uncertainties on the component maps and on the CMB power spectra. For the Planck polarization case they are found to be subdominant compared to noise.Comment: 17 pages, accepted in MNRA