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Register a new userThe number counts, luminosity functions and evolution of microwave-selected (WMAP) blazars and radio galaxies
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Added by
Sergio Colafrancesco
Publication date
2009
fields
Physics
and research's language is
English
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(Abridged) We carried out an extensive search to identify the counterparts of all the sources listed in the WMAP 3-yr catalogue using literature and archival data. Our work led to the identification of 309 WMAP sources, 98% of which are blazars, radio quasars or radio galaxies. At present, 15 objects still remain without identification due to the lack of optical spectroscopic data or a clear radio counterpart. Our results allow us to define a flux limited sample of 203 high Galactic latitude microwave sources ($f_{41GHz} ge 1$ Jy, $|b_{rm II}| > 15^circ$) which is virtually completely identified (99%). The microwave band is ideally suited for blazar statistical studies since this is the part of the em spectrum that is least affected by the superposition of spectral components of different origin. Using this data-set we derived number counts, luminosity functions and cosmological evolution of blazars and radio galaxies at microwave frequencies. Our results are in good agreement with those found at radio frequencies. The 5 GHz bivariate blazar luminosity functions are similar to those derived from the DXRBS survey, which shows that this sample is representative of the blazar population at 41 GHz. Microwave selected broad- lined quasars are about 6 times more abundant than BL Lacs, a ratio that is similar to, or larger than, that seen at radio and gamma-ray frequencies, once spectral selection effects are taken into account. This strongly suggests that the mechanism responsible for the generation of gamma-rays is, at first order, the same in all blazar types. Our results confirm the findings of Giommi & Colafrancesco (2004, 2006) that blazars and radio galaxies are the largest contaminants of the CMB anisotropy maps. We predict that these sources are also bright gamma-ray sources, most of which will be detected by AGILE and FERMI.
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We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies (MCXC; $langle z rangle = 0.14$) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg$^2$ SPT-SZ survey maps at the locations of SUMSS sources, producing a multi-frequency catalog of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev-Zeldovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogs. We find that the high frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then $1.8pm0.7$ percent of the clusters would be lost from the sample. Allowing for redshift evolution of the form $(1+z)^{2.5}$ increases the incompleteness to $5.6pm1.0$ percent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.
Our knowledge of the blazar surface densities and luminosity functions, which are fundamental parameters, relies still on samples at relatively high flux limits. As a result, our understanding of this rare class of active galactic nuclei is mostly based on relatively bright and intrinsically luminous sources. We present the radio number counts, evolutionary properties, and luminosity functions of the faintest blazar sample with basically complete (~ 95%) identifications. Based on the Deep X-ray Radio Blazar Survey (DXRBS), it includes 129 flat-spectrum radio quasars (FSRQ) and 24 BL Lacs down to a 5 GHz flux and power ~ 50 mJy and ~ 10^{24} W/Hz, respectively, an order of magnitude improvement as compared to previously published (radio-selected) blazar samples. DXRBS FSRQ are seen to evolve strongly, up to redshift ~ 1.5, above which high-power sources show a decline in their comoving space density. DXRBS BL Lacs, on the other hand, do not evolve. High-energy (HBL) and low-energy (LBL) peaked BL Lacs share the same lack of cosmological evolution, which is at variance with some previous results. The observed luminosity functions are in good agreement with the predictions of unified schemes, with FSRQ getting close to their expected minimum power. Despite the fact that the large majority of our blazars are FSRQ, BL Lacs are intrinsically ~ 50 times more numerous. Finally, the relative numbers of HBL and LBL in the radio and X-ray bands are different from those predicted by the so-called blazar sequence and support a scenario in which HBL represent a small minority (~ 10%) of all BL Lacs.
(abridged) A detailed comparison is performed of the LFs compiled at infrared, radio and optical wavelengths and converted into XLFs using available relations with the XLF directly estimated in the 0.5--2 keV energy band from X-ray surveys (Norman et al). We find that the XLF from the local sample of IRAS galaxies (Takeuchi et al) provides a good representation of all available data samples; pure luminosity evolution of the form (1+z)^eta, with eta< ~3, is favoured over pure density. The local X-ray luminosity density is also well defined. We discuss different estimates of the galaxies LogN-LogS, selected from the Chandra Deep Fields with different selection criteria: these have similar slopes, but normalisations scattered within a factor ~2, of the same order of the Poissonian error on the counts. We compare the observed LogN-LogS with the counts predicted by integrating our reference z=0 XLF. By using number counts alone, it is not possible to discriminate between density and luminosity evolution; however, the evolution of galaxies must be stopped in both cases at z~1-2. The contribution of galaxies to the X-ray background is found to be in the range 6%--12%. Making use of cosmic star formation models, we find that the X-ray LogN-LogS might be not compatible with very large star formation rates at z ~ 3 as suggested by sub-mm observations in Blain et al. 1999. As to the content of current and, possibly, future X-ray surveys, we determine the fraction of galaxies around the current flux limit: (30+-12 %). At fainter fluxes the fraction of galaxies will probably rise, and overcome the counts from AGN at fluxes < ~10^{-17} erg/s/cm^2.
In this paper we analyse the deep number counts problem, taking account of new observational and theoretical developments. First we show that the new Bruzual and Charlot (1993) models allow a new class of spiral dominated luminosity evolution (LE) model where significant amounts of the luminosity evolution needed to fit faint count data are due to spiral rather than early-type galaxies. Second we show that the inclusion of dust may be a vital ingredient for obtaining fits with any LE model. Third we compare the quality of fit of both the spiral and early-type LE models, including dust, for a wide variety of observational data. We find that parameters can be found for both LE models which allow a good fit to all data with the exception of the faintest B>25 counts in the case of q0=0.5 cosmologies, where some luminosity dependent evolution may be needed (see also Metcalfe et al 1995). Otherwise both these classes of LE model, with the inclusion of dust, provide an excellent foundation for understanding the B<25 galaxy counts and galaxy counts and redshift distributions in a variety of other wavebands.
We present results from the deepest Herschel-PACS (Photodetector Array Camera and Spectrometer) far-infrared blank field extragalactic survey, obtained by combining observations of the GOODS (Great Observatories Origins Deep Survey) fields from the PACS Evolutionary Probe (PEP) and GOODS-Herschel key programmes. We describe data reduction and the construction of images and catalogues. In the deepest parts of the GOODS-S field, the catalogues reach 3-sigma depths of 0.9, 0.6 and 1.3 mJy at 70, 100 and 160 um, respectively, and resolve ~75% of the cosmic infrared background at 100um and 160um into individually detected sources. We use these data to estimate the PACS confusion noise, to derive the PACS number counts down to unprecedented depths and to determine the infrared luminosity function of galaxies down to LIR=10^11 Lsun at z~1 and LIR=10^12 Lsun at z~2, respectively. For the infrared luminosity function of galaxies, our deep Herschel far-infrared observations are fundamental because they provide more accurate infrared luminosity estimates than those previously obtained from mid-infrared observations. Maps and source catalogues (>3-sigma) are now publicly released. Combined with the large wealth of multi-wavelength data available for the GOODS fields, these data provide a powerful new tool for studying galaxy evolution over a broad range of redshifts.
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