A. Comastri

A unifying view of the spectral energy distributions of blazars

ABSTRA C T We collect data at well-sampled frequencies from the radio to the g-ray range for the following three complete samples of blazars: the Slew survey, the 1-Jy samples of BL Lacs and the 2-Jy sample of flat-spectrum radio-loud quasars (FSRQs). The fraction of objects detected in g-rays (E * 100 MeV) is ,17, 26 and 40 per cent in the three samples respectively. Except for the Slew survey sample, g-ray detected sources do not differ either from other sources in each sample, or from all the g-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities or of the broad-band spectral indices (radio to optical and radio to X-ray). We compute average spectral energy distributions (SEDs) from radio to g-rays for each complete sample and for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that (i) the first peak occurs in different frequency ranges for different samples/luminosity classes, with most luminous sources peaking at lower frequencies; (ii) the peak frequency of the g-ray component correlates with the peak frequency of the lower energy one; (iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of sources and the systematic trends of the SEDs as a function of luminosity favour a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQs. The general implications of this unified scheme are discussed while a detailed theoretical analysis, based on fitting continuum models to the individual spectra of most g-ray blazars, is presented in a separate paper.

The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-Ray Mission

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a National Aeronautics and Space Administration (NASA) Small Explorer mission that carried the first focusing hard X-ray (6-79 keV) telescope into orbit. It was launched on a Pegasus rocket into a low-inclination Earth orbit on June 13, 2012, from Reagan Test Site, Kwajalein Atoll. NuSTAR will carry out a two-year primary science mission. The NuSTAR observatory is composed of the X-ray instrument and the spacecraft. The NuSTAR spacecraft is three-axis stabilized with a single articulating solar array based on Orbital Sciences Corporations LEOStar-2 design. The NuSTAR science instrument consists of two co-aligned grazing incidence optics focusing on to two shielded solid state CdZnTe pixel detectors. The instrument was launched in a compact, stowed configuration, and after launch, a 10-meter mast was deployed to achieve a focal length of 10.15 m. The NuSTAR instrument provides sub-arcminute imaging with excellent spectral resolution over a 12-arcminute field of view. The NuSTAR observatory will be operated out of the Mission Operations Center (MOC) at UC Berkeley. Most science targets will be viewed for a week or more. The science data will be transferred from the UC Berkeley MOC to a Science Operations Center (SOC) located at the California Institute of Technology (Caltech). In this paper, we will describe the mission architecture, the technical challenges during the development phase, and the post-launch activities.

A theoretical unifying scheme for gamma-ray bright blazars

ABSTRA C T The phenomenology of g-ray bright blazars can be accounted for by a sequence in the source power and intensity of the diffuse radiation field surrounding the relativistic jet. Correspondingly, the equilibrium particle distribution peaks at different energies. This leads to a trend in the observed properties: an increase of the observed power corresponds to: (i) a decrease in the frequencies of the synchrotron and inverse Compton peaks, and (ii) an increase in the ratio of the powers of the high- and low-energy spectral components. Objects along this sequence would be observationally classified respectively as high-frequency BL Lac objects, lowfrequency BL Lac objects, high-polarization quasars and low-polarization quasars. The proposed scheme is based on the correlations among the physical parameters derived in the present paper by applying to 51 g-ray loud blazars two of the most accepted scenarios for the broad-band emission of blazars, namely the synchrotron self-Compton and external Compton models. This also explains the observational trends presented by Fossati et al., dealing with the spectral energy distributions of all blazars. This gives us confidence that our scheme applies to all blazars as a class.

The 2-10 keV luminosity as a Star Formation Rate indicator

Radio and far infrared luminosities of star-forming galaxies follow a tight linear relation. Making use of ASCA and BeppoSAX observations of a well-defined sample of nearby star-forming galaxies, we argue that tight linear relations hold between the X-ray, radio and far infrared luminosities. The effect of intrinsic absorption is investigated taking NGC3256 as a test case. It is suggested that the hard X-ray emission is directly related to the Star Formation Rate. Star formation processes may also account for most of the 2-10 keV emission from LLAGNs of lower X-ray luminosities (for the same FIRand radio luminosity). Deep Chandra observations of a sample of radio-selected star-forming galaxies in the Hubble Deep Field North show that the same relation holds also at high (0.2 < z < 1.3) redshift. The X-ray/radio relations also allow a derivation of X-ray number counts up to very faint fluxes from the radio Log N-Log S, which is consistent with current limits and models. Thus the contribution of star-forming galaxies to the X-ray background can be estimated.

The First Release COSMOS Optical and Near-IR Data and Catalog*

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3 and 2.4 μm. These include data taken on the Subaru 8.3 m telescope, the KPNO and CTIO 4 m telescopes, and the CFHT 3.6 m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard-star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.

The Chandra COSMOS Survey, I: Overview and Point Source Catalog

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg^2 of the COSMOS field (centered at 10 ^h , +02 ^o ) with an effective exposure of ~160 ks, and an outer 0.4 deg^2 area with an effective exposure of ~80 ks. The limiting source detection depths are 1.9 × 10^(–16) erg cm^(–2) s^(–1) in the soft (0.5-2 keV) band, 7.3 × 10^(–16) erg cm^(–2) s^(–1) in the hard (2-10 keV) band, and 5.7 × 10^(–16) erg cm^(–2) s^(–1) in the full (0.5-10 keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2 × 10^(–5) (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (±12%) exposure across the inner 0.5 deg^2 field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper. The full catalog is described here in detail and is available online.

THE XMM-NEWTON WIDE-FIELD SURVEY IN THE COSMOS FIELD (XMM-COSMOS): DEMOGRAPHY AND MULTIWAVELENGTH PROPERTIES OF OBSCURED AND UNOBSCURED LUMINOUS ACTIVE GALACTIC NUCLEI*

We report the final optical identifications of the medium-depth (~60 ksec), contiguous (2 deg^2) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ~800 X-ray sources down to limiting fluxes of ~5x10^{-16}, ~3x10^{-15}, and ~7x10^{-15} erg/cm2/s in the 0.5-2 keV, 2-10 keV and 5-10 keV bands, respectively. The work is complemented by an extensive collection of multi-wavelength data from 24 micron to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for ~50% of the sample, and high-quality photometric redshifts for the rest. The XMM and multiwavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (~95%) have IRAC counterparts, and 1394 (~78%) have MIPS 24micron detections. Thanks to the redshift completeness (almost 100%) we were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of logL_X>44.5 AGN is at z~2. Spectroscopically-identified obscured and unobscured AGN, as well as normal and starforming galaxies, present well-defined optical and infrared properties. We devised a robust method to identify a sample of ~150 high redshift (z>1), obscured AGN candidates for which optical spectroscopy is not available. We were able to determine that the fraction of the obscured AGN population at the highest (L_X>10^{44} erg s^{-1}) X-ray luminosity is ~15-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. We studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO, caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations.

Unveiling Obscured Accretion in the Chandra Deep Field-South

We make use of deep HST, VLT, Spitzer, and Chandra data on the Chandra Deep Field-South to constrain the number of Compton-thick AGNs in this field. We show that sources with high 24 μm-to-optical flux ratios and red colors form a distinct source population, and that their infrared luminosity is dominated by AGN emission. Analysis of the X-ray properties of these extreme sources shows that most of them (80% ± 15%) are indeed likely to be highly obscured, Compton-thick AGNs. The number of infrared-selected, Compton-thick AGNs with 5.8 μm luminosity higher than 1044.2 ergs s−1 turns out to be similar to that of X-ray-selected, unobscured, and moderately obscured AGNs with 2-10 keV luminosity higher than 1043 ergs s−1 in the redshift bin 1.2-2.6. This factor of 2 source population is exactly what is needed to solve the discrepancies between model predictions and X-ray AGN selection.

ON THE COSMIC EVOLUTION OF THE SCALING RELATIONS BETWEEN BLACK HOLES AND THEIR HOST GALAXIES : BROAD-LINE ACTIVE GALACTIC NUCLEI IN THE ZCOSMOS SURVEY

We report on the measurement of the physical properties (rest-frame K-band luminosity and total stellar mass) of the hosts of 89 broad-line (type-1) active galactic nuclei (AGNs) detected in the zCOSMOS survey in the redshift range 1 < z < 2.2. The unprecedented multi-wavelength coverage of the survey field allows us to disentangle the emission of the host galaxy from that of the nuclear black hole in their spectral energy distributions (SEDs). We derive an estimate of black hole masses through the analysis of the broad Mg II emission lines observed in the medium-resolution spectra taken with VIMOS/VLT as part of the zCOSMOS project. We found that, as compared to the local value, the average black hole to host-galaxy mass ratio appears to evolve positively with redshift, with a best-fit evolution of the form (1 + z)^[(0.68±0.12)^(+0.6)_(-0.3)], where the large asymmetric systematic errors stem from the uncertainties in the choice of initial mass function, in the calibration of the virial relation used to estimate BH masses and in the mean QSO SED adopted. On the other hand, if we consider the observed rest-frame K-band luminosity, objects tend to be brighter, for a given black hole mass, than those on the local M_(BH)-M_K relation. This fact, together with more indirect evidence from the SED fitting itself, suggests that the AGN hosts are likely actively star-forming galaxies. A thorough analysis of observational biases induced by intrinsic scatter in the scaling relations reinforces the conclusion that an evolution of the M_(BH)-M_* relation must ensue for actively growing black holes at early times: either its overall normalization, or its intrinsic scatter (or both) appear to increase with redshift. This can be interpreted as signature of either a more rapid growth of supermassive black holes at high redshift, a change of structural properties of AGN hosts at earlier times, or a significant mismatch between the typical growth times of nuclear black holes and host galaxies. In any case, our results provide important clues on the nature of the early co-evolution of black holes and galaxies and challenging tests for models of AGN feedback and self-regulated growth of structures.

The XMM-Newton Wide-Field Survey in the COSMOS Field. I. Survey Description

We present the first set of XMM-Newton EPIC observations in the 2 deg^2 COSMOS field. The strength of the COSMOS project is the unprecedented combination of a large solid angle and sensitivity over the whole multiwavelength spectrum. The XMM-Newton observations are very efficient in localizing and identifying active galactic nuclei (AGNs) and clusters, as well as groups of galaxies. One of the primary goals of the XMM-Newton Cosmos survey is to study the coevolution of active galactic nuclei as a function of their environment in the cosmic web. Here we present the log of observations, images, and a summary of first research highlights for the first pass of 25 XMM-Newton pointings across the field. In the existing data set we have detected 1416 new X-ray sources in the 0.5-2, 2-4.5, and 4.5-10 keV bands to an equivalent 0.5-2 keV flux limit of 7 × 10^(-16) erg cm^(-2) s^(-1). The number of sources is expected to grow to almost 2000 in the final coverage of the survey. From an X-ray color-color analysis we identify a population of heavily obscured, partially leaky or reflecting absorbers, most of which are likely to be nearby, Compton-thick AGNs.