Search

We investigate the astrophysics of radio-emitting star-forming galaxies and ac- tive galactic nuclei (AGNs), and elucidate their statistical properties in the radio band including luminosity functions, redshift distributions, and number counts at sub-mJy flux levels, that will be crucially probed by next-generation radio continuum surveys. Specifically, we exploit the model-independent approach by Mancuso et al. (2016a,b) to compute the star formation rate functions, the AGN duty cycles and the conditional probability of a star-forming galaxy to host an AGN with given bolometric luminosity. Coupling these ingredients with the radio emission properties associated to star formation and nuclear activity, we compute relevant statistics at different radio frequencies, and disentangle the relative con- tribution of star-forming galaxies and AGNs in different radio luminosity, radio flux, and redshift ranges. Finally, we highlight that radio-emitting star-forming galaxies and AGNs are expected to host supermassive black holes accreting with different Eddington ratio distributions, and to occupy different loci in the galaxy main sequence diagrams. These specific predictions are consistent with current datasets, but need to be tested with larger statistics via future radio data with multi-band coverage on wide areas, as it will become routinely achievable with the advent of the SKA and its precursors., Comment: 50 pages, 16 figures, Accepted by ApJ

We have investigated the Cosmic Infrared Background (CIB) anisotropies in the framework of the physical evolutionary model for proto-spheroidal galaxies by Granato et al. (2004). After having re-calibrated the cumulative flux function $dS/dz$ at $\lambda \ge 850\,\mu$m using the available determinations of the shot noise amplitude (the original model already correctly reproduces it at shorter wavelengths) the CIB power spectra at wavelengths from $250\,\mu$m to $2\,$mm measured by {\it Planck}, {\it Herschel}, SPT and ACT experiments have been fitted using the halo model with only 2 free parameters, the minimum halo mass and the power-law index of the mean occupation function of satellite galaxies. The best-fit {\it minimum} halo mass is $\log(M_{\rm min}/M_\odot) = 12.24 \pm 0.06$, higher than, but consistent within the errors, with the estimate by Amblard et al. (2011) and close to the estimate by Planck Collaboration (2011). The redshift evolution of the volume emissivity of galaxies yielded by the model is found to be consistent with that inferred from the data. The derived {\it effective} halo mass, $M_{\rm eff} \simeq 5\times 10^{12}\,M_\odot$, of $z\simeq 2$ sub-millimeter galaxies is close to that estimated for the most efficient star-formers at the same redshift. The effective bias factor and the comoving clustering radius at $z\simeq 2$ yielded by the model are substantially lower than those found for a model whereby the star formation is fueled by steady gas accretion, but substantially higher than those found for a merging-driven galaxy evolution with a top-heavy initial mass function.

We present a quantitative analysis of the astrophysical and cosmological information that can be extracted from the many important wide-area, shallow surveys that will be carried out in the next few years. Our calculations combine the predictions of the physical model by Granato et al. (2004) for the formation and evolution of spheroidal galaxies with up-to-date phenomenological models for the evolution of starburst and normal late-type galaxies and of radio sources. We compute the expected number counts and the redshift distributions of these source populations separately and then focus on proto-spheroidal galaxies. For the latter objects we predict the counts and redshift distributions of strongly lensed sources at 250, 350, 500, and 850 micron, the angular correlation function of sources detected in the surveys considered, the angular power spectra due to clustering of sources below the detection limit in Herschel and Planck surveys. An optimal survey for selecting strongly lensed proto-spheroidal galaxies is described, and it is shown how they can be easily distinguished from the other source populations. We also discuss the detectability of the imprints of the 1-halo and 2-halo regimes on angular correlation functions and clustering power spectra, as well as the constraints on cosmological parameters that can be obtained from the determinations of these quantities. The novel data relevant to derive the first sub-millimeter estimates of the local luminosity functions of starburst and late-type galaxies, and the constraints on the properties of rare source populations, such as blazars, are also briefly described., 16 pages, 10 figures. Accepted for publication on MNRAS

We have combined determinations of the epoch-dependent star formation rate (SFR) function with relationships between SFR and radio (synchrotron and free-free) emission to work out detailed predictions for the counts and the redshift distributions of star-forming galaxies detected by planned Square Kilometer Array (SKA) surveys. The evolving SFR function comes from recent models fitting the far-infrared (FIR) to millimeter-wave luminosity functions and the ultraviolet (UV) luminosity functions up to z=10, extended to take into account additional UV survey data. We used very deep 1.4 GHz number counts from the literature to check the relationship between SFR and synchrotron emission, and the 95 GHz South Pole Telescope (SPT) counts of dusty galaxies to test the relationship between SFR and free-free emission. We show that the SKA will allow us to investigate the SFRs of galaxies down to few Msun/yr up to z=10, thus extending by more than two orders of magnitude the high-z SFR functions derived from Herschel surveys. SKA1-MID surveys, down to microJy levels, will detect hundreds of strongly lensed galaxies per square degree; a substantial fraction of them will show at least two images above the detection limits., Comment: 11 pages, 4 figures, to appear in proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)082

We show that the observed Velocity Dispersion Function of E/S0 galaxies matches strikingly well the distribution function of virial velocities of massive halos virializing at z > 1.5, as predicted by the standard hierarchical clustering scenario in a \LambdaCDM cosmology, for a constant ratio sigma/V_vir = 0.55 \pm 0.05, close to the value expected at virialization if it typically occurred at z > 3. This strongly suggests that dissipative processes and later merging events had little impact on the matter density profile. Adopting the above sigma/V_vir ratio, the observed relationships between photometric and dynamical properties which define the fundamental plane of elliptical galaxies, such as the luminosity-sigma (Faber-Jackson) and the luminosity-effective radius relations, as well as the M_BH-sigma relation, are nicely reproduced. Their shapes turn out to be determined by the mutual feedback of star-formation (and supernova explosions)and nuclear activity, along the lines discussed by Granato et al. (2004). To our knowledge, this is the first semi-analytic model for which simultaneous fits of the fundamental plane relations and of the epoch-dependent luminosity function of spheroidal galaxies have been presented.

We present a multi-wavelength catalog (15 um, R, K-band, 1.4 GHz flux) plus spectroscopic identifications for 406 15 um sources detected in the ELAIS region S1, over the flux density range 0.5, Comment: Scheduled on AJ, Vol. 127/6, 2004 June. Table 2 (+ 15um sources coordinates) at http://www.fis.uniroma3.it/~ELAIS_S/lafrancabab.tab2.dat . Table 3 at http://www.fis.uniroma3.it/~ELAIS_S/lafrancabab.tab3.dat . Other related data and papers at http://www.fis.uniroma3.it/~ELAIS_S/ . Few luminosities in Table 2 corrected

Based on observations obtained with Planck (http://www.esa.int/Planck), an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada.-- et al., We present the first measurement of the correlation between the map of the cosmic microwave background (CMB) lensing potential derived from the Planck nominal mission data and galaxies detected by the Herschel-ATLAS (H-ATLAS) survey covering about , i.e., about 1.4% of the sky. We reject the hypothesis that there is no correlation between CMB lensing and galaxy detection at asignificance, checking the result by performing a number of null tests. The significance of the detection of the theoretically expected cross-correlation signal is found to be. The galaxy bias parameter, b, derived from a joint analysis of the cross-power spectrum and of the autopower spectrum of the galaxy density contrast is found to be , consistent with earlier estimates for H-ATLAS galaxies at similar redshifts. On the other hand, the amplitude of the cross-correlation is found to be a factor 1.62 ± 0.16 higher than expected from the standard model and also found by cross-correlation analyses with other tracers of the large-scale structure. The enhancement due to lensing magnification can account for only a fraction of the excess cross-correlation signal. We suggest that part of it may be due to an incomplete removal of the contamination of the cosmic infrared background, which includes the H-ATLAS sources we are cross-correlating with. In any case, the highly significant detection reported here using a catalog covering only 1.4% of the sky demonstrates the potential of CMB lensing correlations with submillimeter surveys., We gratefully acknowledge support from INAF PRIN 2012/2013 >Looking into the dust-obscured phase of galaxy formation through cosmic zoom lenses in the Herschel Astrophysical Terahertz Large Area Survey,> and from ASI/INAF agreement 2014-024 R.0. F.B. acknowledges partial support from the INFN-INDARK initiative. L.D., R.J.I., and S.M. acknowledge support from the European Research Council (ERC) in the form of Advanced Investigator Program COSMICISM. J.G.N. acknowledges financial support from the Spanish CSIC for a JAE-DOC fellowship, cofunded by the European Social Fund. The work has been supported in part by the Spanish Ministerio de Ciencia e Innovacion, AYA2012-39475-C02-01, and Consolider-Ingenio 2010, CSD2010-00064, projects.

We have used the Very Large Array(VLA) in C configuration to carry out a sensitive 20cm radio survey of regions of sky that have been surveyed in the Far Infra-Red over the wavelength range 5-200 microns with ISO as part of the European Large Area ISO Survey(ELAIS). As usual in surveys based on a relatively small number of overlapping VLA pointings the flux limit varies over the area surveyed. The survey has a flux limit that varies from a 5$\sigma$ limit of 0.135mJy over an area of 0.12deg$^2$ to a 5$\sigma$ limit of 1.15mJy or better over the whole region covered of 4.22 deg$^2$. In this paper we present the radio catalogue of 867 sources. These regions of sky have previously been surveyed to shallow flux limits at 20cm with the VLA as part of the VLA D configuration NVSS(FWHM=45 arcsec) and VLA B configuration FIRST(FWHM=5 arcsec) surveys. We have carried out a a detailed comparison of the reliability of our own survey and these two independent surveys in order to assess the reliability and completeness of each survey., Comment: 19 pages, 24 figures, submitted to MNRAS, also available in http://www.ast.cam.ac.uk/~ciliegi/elais/papers

The COBRAS/SAMBA mission is designed for extensive, accurate mapping of the anisotropy of the Cosmic Background Radiation. with angular sensitivity from scales of a few arcminutes up to and overlapping with the > 7° COBE-DMR resolution. This will allow a full identification of the primordial density perturbations which grew to Corm the large-scale structures observed in the present universe. The COBRAS/SAMBA maps will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early universe and the origin of cosmic structure. One of the main diffuse foreground emissions will be from interstellar dust, and the mission will provide relevant information on its components and emission properties. A combination of bolometric and radiometric detection techniques will ensure the sensitivity and wide spectral coverage required for accurate foreground discrimination. A far-Earth orbit has been selected to minimize the unwanted emission from the Earth as a source of contamination. The project is currently undergoing a feasibility study within the European Space Agency M3 programme.

Current limits on the intensity of the extragalactic infrared background are consistent with the expected contribution from evolving galaxies. Depending on the behaviour of the star formation rate and of the initial mass function, we can expect that dust extinction during early evolutionary phases ranges from moderate to strong. An example of the latter case may be the ultraluminous galaxy IRAS F$10214 + 4724$. The remarkable lack of high redshift galaxies in faint optically selected samples may be indirect evidence that strong extinction is common during early phases. Testable implications of different scenarios are discussed; ISO can play a key role in this context. Estimates of possible contributions of galaxies to the background under different assumptions are presented. The COBE/FIRAS limits on deviations from a blackbody spectrum at sub-mm wavelengths already set important constraints on the evolution of the far-IR emission of galaxies and on the density of obscured (``Type 2'') AGNs. A major progress in the field is expected at the completion of the analysis of COBE/DIRBE data.

Ground-based measurements of the Cosmic Background Radiation (CBR) are hampered by emission from atmospheric O2 and water molecules. We performed multifrequency measurements of the atmospheric emission in the 1–90 GHz spectral range from two high-altitude sites (White Mountain, California, and South Pole, Antarctica). A power spectrum analysis of our data shows variations of the atmospheric antenna temperature which exceed, on time scales of a few hours or more, those expected from radiometer noise and changes in water column density. When combined with real-time measurements of the local profiles of atmospheric pressure, temperature and humidity, our results indicate variations of order 10% of the O2 emission (both resonant and non-resonant components) on time scales of hours to days, driven by the evolution of the atmospheric pressure profile. These oxygen emission fluctuations appear significantly larger than previously expected, and may affect ground-based CBR experiments

We report the results of a thorough analysis of the evolutionary properties of active galactic nuclei, exploiting data from both hard and soft X-ray surveys [counts, luminosity and redshift distributions, average X-ray spectral properties and P(D) distributions]. Strong indications are found that soft (< 3 keV) and hard X-ray surveys emphasize two distinct classes of AGN that have different X-ray spectra, luminosity functions and evolution. Soft X-ray AGN have higher luminosities, steep source-count slopes and high evolution rates, similar to those of optically selected QSOs; their contribution to the 2-10 keV X-ray background (XRB) is probably < 20 per cent. Hard X-ray AGN have relatively low luminosities and strong photoelectric absorption

We show that the ABC scenario we proposed for the co-evolution of spheroids and QSOs predicts accretion rates and masses of supermassive black holes in sub-mm galaxies in keeping with recent X-ray determinations. These masses are well below the local values, and those predicted by alternative models. The observed column densities may be mostly due to ISM in the galaxy. The contribution of the associated nuclear activity to the X-ray background is likely negligible, while they may contribute a sizeable fraction $\sim 10 %$ to hard-X cumulative counts at the faintest observed fluxes., Comment: 5 pages 4 figures, MNRAS letters, accepted

We present the final band-merged ELAIS catalogue at 6.7, 15, 90, and 175 $��$m, and the associated data at u,g,r,i,z,J,H,K, and 20cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered, and completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total catalogues consists of 2860 sources. For extragalactic sources observed in 3 or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and AGN dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the INT ugriz Wide Field Survey, permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies in the ELAIS Catalogue ($> 10 %$ of 15 $��$m sources), many with Arp220-like colours. 10 hyperluminous infrared galaxies and 10 EROs are found in the survey. The large numbers of ultraluminous galaxies imply very strong evolution in the star-formation rate between z = 0 and 1., 21 pages, 31 figures. Accepted for publication in MNRAS

We summarize our detailed, physically grounded, model for the early co-evolution of spheroidal galaxies and of active nuclei at their centers (astro-ph/0307202). Our predictions are 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. Also, the black hole mass function and the relationship between the black hole mass and the velocity dispersion in the galaxy are nicely reproduced., Comment: 4 pages, 5 figures, to appear in Proceeding of the "Multi-Wavelength Cosmology" Conference held in Mykonos, Greece, June 2003, ed. M. Plionis (Kluwer)

We present the 15-mum luminosity function of type 1 active galactic nuclei (AGN1; quasi-stellar object+Seyfert 1). Our sample of 21 high-redshift sources is selected from the Preliminary Analysis catalogue in the S1 field of the European Large Area ISO Survey (ELAIS). To study the cosmological evolution of the AGN1 luminosity function, our sample has been combined with a local sample of 41 sources observed by IRAS . We find that the luminosity function of AGN1 at 15 mum is fairly well represented by a double-power-law-function. There is evidence for significant cosmological evolution consistent with a pure luminosity evolution (PLE) model L(z )proportional to(1+z ) (kL), with k(L) =3.0-3.3. The value of k(L) depends on the existence or non-existence of an evolution cut-off at redshift similar to2, and on the adopted cosmology. From the luminosity function and its evolution we estimate a contribution of AGN1 to the cosmic infrared background (CIRB) of nuI(nu) similar to 6x10(-11) W m(-2) sr(-1) at 15 mum. This corresponds to similar to2-3 per cent of the total observed CIRB at this wavelength. Under the usual assumptions of unified models for AGN, the expected contribution of the whole AGN population to the CIRB at 15 mum is 10-15 per cent.

This paper investigates the clustering properties of SCUBA-selected galaxies in the framework of a unifying scheme relating the formation of QSOs and spheroids (Granato et al. 2000). The theoretical angular correlation function is derived for different bias functions, corresponding to different values of the ratio $M_{\rm halo}/M_{\rm sph}$ between the mass of the dark halo and the final mass in stars. SCUBA sources are predicted to be strongly clustered, with a clustering strength increasing with mass. We show that the model accounts for the clustering of Lyman-break Galaxies, seen as the optical counterpart of low- to intermediate-mass primeval spheroidal galaxies and is also consistent with the observed angular correlation function of Extremely Red Objects. Best agreement is obtained for $M_{\rm halo}/M_{\rm sph}=100$. We also consider the implications for small scale fluctuations observed at sub-mm wavelengths by current or forthcoming experiments aimed at mapping the Cosmic Microwave Background (CMB). The predicted amplitude of the clustering signal in the 350 GHz channel of the Planck mission strongly depends on the halo-to-bulge mass ratio and may be of comparable amplitude to primary CMB anisotropies for multipole numbers $l\simgt 50$., 7 pages, 5 figures, to appear in MNRAS

We present results and source counts at 90micron extracted from the Preliminary Analysis of the European Large Area ISO Survey (ELAIS). The survey covered about 11.6 square degrees of the sky in four main areas and was carried out with the PHOT instrument onboard the Infrared Space Observatory (ISO). The survey is at least an order of magnitude deeper than the IRAS 100micron survey and is expected to provide constraints on the formation and evolution of galaxies. The majority of the detected sources are associated with galaxies on optical images. In some cases the optical associations are interacting pairs or small groups of galaxies suggesting the sample may include a significant fraction of luminous infrared galaxies. The source counts extracted from a reliable subset of the detected sources are in agreement with strongly evolving models of the starburst galaxy population., 13 pages, accepted by MNRAS. For more details on the ELAIS project see http://athena.ph.ic.ac.uk/

I describe a project to survey ∼ 13 square degrees of the sky at 15μm and 90μm with the Infrared Space Observatory (ISO). The European Large Area ISO Survey (ELAIS) is a collaboration involving 19 European institutes (in addition to the authors and others at their institutes the following people and others their institutes are involved I. Gonzalez-Serrano, E. Kontizas, K. Mandolesi, J. Masegosa, K. Mattila, H. Norgaard-Nielsen, I. Perez-Fournon, M. Ward) and is the largest open time project being undertaken by ISO. We expect to detect at least 1000 extra-galactic objects and a similar number of Galactic sources.

Surveys with ISO (Kessler et al 1996), in particular with the CAM (Cesarsky et al 1996) and PHOT (Lemke et al 1996) instruments, will greatly extend our understanding of extra-galactic populations and their cosmological evolution. The main advantages that ISO surveys have over e.g IRAS are increased sensitivity/depth and wavelength coverage. Within the Guaranteed and Open Time programmes there are many field surveys which will efficiently map the limits in these parameters. In this talk I will briefly overview those surveys before concentrating in more detail on one survey in particular, the ISO survey of the Hubble Deep Field (HDF), to illustrate the kind of results that can be expected.

We review various survey programs currently under execution by the Infrared Space Observatory, and to which an important fraction of the total mission time is devoted. In spite of the small primary collector, ISO is expected to provide results of relevant cosmological impact, especially to test rival scenarios of galaxy and quasar formation.

The IR spectra of broad‐ and narrow‐line Active Galactic Nuclei (AGN) are modelled on the assumption of existence of dust tori around the active nuclei. The outcomes of the model are compared with broad IR spectra, visibility of broad lines in the IR, the extension of the IR emission and the X‐ray properties of type 1 and 2 AGN. The contribution to the mid‐IR background is then estimated properly taking into account local Luminosity Functions, cosmological evolution and spectral properties. Under plausible assumptions, the (dusty) AGN may yield a significant fraction of the extragalactic background in the range 10–50 μm.

We discuss plausible contributions from evolving galaxies to the cosmic infrared background (CIRB). These estimates are based on two alternative evolutionary paradigms, roughly consistent with currently available data. One scheme is a combination of luminosity and density evolution, and assumes that galaxy evolution from optical through radio wavelengths is driven by substantial merging events, increasing the average galactic mass with cosmic time and triggering star formation in the gas‐rich systems. The other extreme pattern assumes a constant mass function up to the formation epoch and pure luminosity evolution. In such a case, early‐formed dust is assumed to hide from optical searches the expected bright star‐formation phase of spheroidal galaxies. The corresponding dust re‐radiation in the far‐IR may have been, during these early phases, orders of magnitude larger than today, as possibly indicated by long‐wavelength observations of hyperluminous IRAS galaxies, high redshift radio galaxies and quasars. We show that the rates of luminosity/density evolution, which determine the amount of energy radiated by galaxies in the IR, are very roughly constrained by the IRAS galaxy counts (also complemented by faint radio and K‐band counts, and, hopefully, by the forthcoming deep ISO surveys). On the other hand, the precise shape of the CIRB spectrum depends on evolution effects in the average dust temperature, which is likely to increase during the past active star‐forming phases as a consequence of the increased radiation field. Galaxies are the likely dominant sources of the IR background. A further significant contribution is expected in the mid‐ and far‐IR from dust‐enshrouded AGNs, which in the framework of unified models are expected to be numerous and strongly evolving. Altogether, most of the observed background level, after subtraction of the obvious Galactic and Zodiacal foregrounds, appears to be due to the integrated contribution of known source populations. In the near‐IR cosmological window in particular, any residual signals ‐ e.g. due to radiation processes occurring at very high redshifts ‐ are bound not to exceed relatively low intensity levels.

16 páginas, 14 figuras, 3 tablas.-- Planck Collaboration: et al., The European Space Agency’s Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009. Its performance is well in line with expectations, and it will continue to gather scientific data until the end of its cryogenic lifetime. We give an overview of the history of Planck in its first year of operations, and describe some of the key performance aspects of the satellite. This paper is part of a package submitted in conjunction with Planck’s Early Release Compact Source Catalogue, the first data product based on Planck to be released publicly. The package describes the scientific performance of the Planck payload, and presents results on a variety of astrophysical topics related to the sources included in the Catalogue, as well as selected topics on diffuse emission., The Planck Collaboration acknowledges the support of: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN and JA (Spain); Tekes, AoF and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and DEISA (EU).

HEAO 1 A-2 all-sky survey data have been used to determine the amplitude of intensity fluctuations of the extragalactic 2-10 keV X-ray background (XRB) over an effective solid angle of 1.84 sq deg and their angular correlation function on angular scales of less than 3 deg. A good empirical fit to the data is obtained assuming that the integral counts in the A-2 band have a slope of 1.65 + 0.06 or - 0.07. Alternatively, the data may imply a significant clustering of extragalactic X-ray sources.

We have carried out an extensive numerical analysis of distortions of the microwave background spectrum that can arise over a broad interval of cosmic times. The range of validity of existing analytic approximation formulae, holding for large and very small values of the Comptonization parameter y, has been assessed and the shape of distortions that can arise for intermediate values of y has been determined. From a comparison with existing spectral data we have derived upper limits to the amount of energy that could have been dissipated at each cosmic time. The effectiveness of future measurements in tightening such constraints is discussed

The spectral distortions of the Cosmic Microwave Background (CMB) are quite informative on the processes that might (or had to) occur in the primordial plasma after the thermalization time, during an epoch which is crucial for the formation of the observed structures of the universe. Here we review the relevant processes generating CMB spectral distortions. We compare the presently available data on the spectrum with the predictions of a variety of theoretical scenarios. We also review the connections among the spectral shape of the CMB, the dipole anisotropy and the Sunyaev-Zeldovich effect.

The HEAO–1 A2 scanning survey has provided small field-of-view data characterized by a full width zero intensity of 3° along the scan direction (at approximately constant ecliptic longitude λ) and of 6° perpendicular to it. We have used independent fields taken from scanning circles separated by Δλ = 6° and whose centers are separated by Δβ = 3°. After having excluded all fields at | β | < 60° or at | b | ≤ 20°, only 905 of the total turned out to be not significantly contaminated by diffuse galactic emission or by known discrete sources. The flux intensity at each field's central position was evaluated by fitting a point source plus a constant background. The sample average C (θ) of the products dI (θ) x dI'(θ + Δθ) of positive and negative intensity fluctuations computed for angular separations of 3°, 6°, …, and 27° provides the X-ray background (XRB) angular correlation function.

We present CCD observations in BVR optical bands of the homogeneous sample of 42 Seyfert 1 galaxies, that we also observed in near-IR JHK bands (Zitelli et al. 1993; Danese et al. 1992). We have applied to these data the same analysis procedure used for the infrared images, with the aim of separating the galaxian and nuclear fluxes, as well as investigating the main characteristics of the hosts. Nuclear fluxes have been estimated with typical global errors of 0.15 mag, while 0.3 mag errors are on average associated to host galaxy magnitudes. It is shown that in half of the host galaxies the bulge contribute more than 40% to the total observed fluxes even within small apertures. In the sample galaxies disks are dominating over the bulge in the large majority of the cases, suggesting that a significant fraction of Seyfert galaxies could be late-type spirals. Moreover the galactic morphological parameters are in the ranges of typical spiral galaxies

New imaging and photometric IR data have been used to discuss the properties of nuclei and hosting galaxies of a well-defined and large sample of optically selected Seyfert 1 galaxies. The K-band luminosity distribution of galaxies hosting the active nuclei has been derived, and the comparison with the local luminosity function of the spirals confirms that the probability of a spiral galaxy hosting bright AGNs increases with the luminosity. On average, the colors of the galaxies are slightly redder than those of spirals, suggesting that hosting galaxies usually have moderately enhanced star formation rates

Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.

Les donnees du satellite IRAS et d'Arecibo a 2.4 GHz sur un echantillon de 1671 galaxies sont traitees statistiquement pour etudier l'evolution de la fonction de luminosite du visible au domaine radio en passant par l'IR lointain

L'exploitation des donnees IRAS, en etroite correlation avec l'observation radio recente de galaxies actives, permet d'etudier l'evolution cosmologique de ces objets et de conforter certains modeles theoriques, en particulier sur les predictions faites sur le flux a 60 μm

We have continued our program to measure the long-wavelength spectrum of the cosmic background radiation. Our previous observations were at five wavelengths--0.33, 0.9, 3.0, 6.3, and 12.0 cm--and had a weighted average value of 2.73 {+-} 0.05 K and deviated from a Planckian spectrum by less than 6%. In August 1984, we repeated our observations at 3.0, 0.9, and 0.33 cm and made new observations with a radiometer tunable from 1.7 to 15 cm. Preliminary analysis indicate that the new data are consistent with our previous results.

Source counts which now extend to surface densities of ∼105 sources/sr make possible a direct evaluation of the radio source contribution to the small-scale fluctuations in the microwave background on scales larger than ∼10′, at wavelengths cm. Comprehensive radio spectral data permit a straightforward and largely model-independent extrapolation of the N(S) relation to shorter wavelengths. On the other hand, Peacock and Gull (1981, hereafter PG) have constructed a set of models which incorporate a wealth of additional data, such as local luminosity functions, luminosity/redshift distributions, luminosity-spectral index correlations; they can therefore be exploited to optimize the extrapolations both to higher frequencies and to fainter flux densities. Only one of these models, however, namely No. 4, is consistent with the recent P(D) results (Wall et al. 1982; Ledden et al. 1980) which provide information on the areal density of sources at s~1mJy; therefore, in the following we shall focus on it.

We have analyzed the HEAO-1 A2 all-sky survey data to investigate the autocorrelation function of the surface brightness fluctuations of the extra-galactic 2–10 keV X-ray background on angular scales ranging from 3° to 27°. No significant signal has been detected on any scale. The derived upper limits set important bounds on correlated emission on scales ≥ 10 Mpc. X-ray data are found to be compatible with optical estimates of the two-point spatial correlation function of rich clusters of galaxies and with recent predictions for their cosmological evolution. Constraints on clustering of Active Galactic Nuclei (AGNs) and on its dependence on cosmic time are analyzed in the light of results of recent optical studies. We also discuss bounds on very large scale structures, on correlations between AGNs and clusters and between clumps of hot gas.

We review all the relevant information on the cosmological evolution of extragalactic sources. We show that the evolution of Active Galactic Nuclei selected at radio, optical and X-ray wavebands is well represented by simple Luminosity Evolution models. A population of Actively Star Forming galaxies is also found to evolve on time scales similar to those of AGNs. Finally, we touch on the problem of the physical interpretation of the cosmological evolution for these source populations.