L. Chiappetti

Spectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey

We present the spectral energy distributions (SEDs) of a hard X-ray selected sample. The sample contains 136 sources with F(2-10 keV)>10^-14 erg/cm^2/s and 132 are AGNs. The sources are detected in a 1 square degree area of the XMM-Newton-Medium Deep Survey where optical data from the VVDS, CFHTLS surveys, and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with sigma(1+z)=0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17+9-6% of AGNs shows star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33+6-1%) and AGN2 (50+6-11). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the IR SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L(3-20micron)/Lcorr(0.5-10 keV) ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E>10 keV are too faint to be detected even in the deepest current radio surveys.We present the SEDs of a hard X-ray selected sample containing 136 sources with F_(2-10 keV) > 10^(-14) erg cm^(-2) s^(-1); 132 are AGNs. The sources are detected in a 1 deg^2 area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with σ(1 + z) = 0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17^(+9)_(-6)% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33^(+6)_(-1)%) and AGN2 (50^(+6)_(-11)%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L_(3-20 μm)/L^(corr)_(0.5-10 keV) ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E > 10 keV are too faint to be detected even in the deepest current radio surveys.

The XMM-LSS survey: the Class 1 cluster sample over the initial 5 deg2 and its cosmological modelling

We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the objects being groups with a temperature below 2 keV. Our L-T(z) relation points toward self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z=1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the L-T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10deg2 has the potential to exclude the non-evolution hypothesis, but that constraints on more refined ICM models will probably be limited by the large intrinsic dispersion of the L-T relation. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and T(M,z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass-flux and mass-count-rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming SZ surveys.

The XMM-LSS survey. Survey design and first results

We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0

Definition of the Flexible Image Transport System (FITS), version 3.0

The Flexible Image Transport System (FITS) has been used by astronomers for over 30 years as a data interchange and archiving format; FITS files are now handled by a wide range of astronomical software packages. Since the FITS format definition document (the “standard”) was last printed in this journal in 2001, several new features have been developed and standardized, notably support for 64-bit integers in images and tables, variable-length arrays in tables, and new world coordinate system conventions which provide a mapping from an element in a data array to a physical coordinate on the sky or within a spectrum. The FITS Working Group of the International Astronomical Union has therefore produced this new version 3.0 of the FITS standard, which is provided here in its entirety. In addition to describing the new features in FITS, numerous editorial changes were made to the previous version to clarify and reorganize many of the sections. Also included are some appendices which are not formally part of the standard. The FITS standard is likely to undergo further evolution, in which case the latest version may be found on the FITS Support Office Web site at http://fits.gsfc.nasa.gov/, which also provides many links to FITS-related resources.

Broadband Spectrum of Cygnus X-1 in Two Spectral States with BeppoSAX

We report on the 0.5-200 keV spectral properties of Cyg X-1 observed at different epochs with the Narrow Field Instruments of the BeppoSAX satellite. The source was in its soft state during the first observation of 1996 June. In the second observation of 1996 September, the source had parameters characteristic to its hard state. A soft X-ray excess, a broad Fe Kα line and Compton reflection are clearly detected in both states. The soft-state broadband continuum is well modeled by a disk blackbody (accounting for the soft excess) and Compton upscattering of the disk photons by a hybrid, thermal/nonthermal plasma, probably forming a corona above the disk (also giving rise to the Compton-reflection component). In the hard state, the primary hard X-ray spectrum can be well modeled by Compton upscattering of a weak blackbody emission by a thermal plasma at a temperature of ~60 keV. The soft excess is then explained by thermal Comptonization of the same blackbody emission by another hot plasma cloud characterized by a low value of its Compton parameter. Finally, we find the characteristic ratio of the bolometric flux in the soft state to that in the hard state to be about 3. This value is much more compatible with theories of state transitions than the previously reported (and likely underestimated) value of 1.5.

The XMM Large-Scale Structure survey: the X-ray pipeline and survey selection function

We present the X-ray pipeline developed for the purpose of the cluster search in the XMM-LSS survey. It is based on a two-stage procedure via a dedicated handling of the Poisson nature of the signal: (1) source detection on multi-resolution wavelet filtered images; (2) source analysis by means of a maximum likelihood fit to the photon images. The source detection efficiency and characterisation are studied through extensive Monte-Carlo simulations. This led us to define two samples of extended sources: the C1 class that is uncontaminated, and the less restrictive C2 class that allows for 50% contamination. The resulting predicted selection function is presented and the comparison to the current XMM-LSS confirmed cluster sample shows very good agreement. We arrive at average predicted source densities of about 7 C1 and 12 C2 per deg 2 , which is higher than any available wide field X-ray survey. We finally notice a substantial deviation of the predicted redshift distribution for our samples from the one obtained using the usual assumption of a flux limited sample.

The XMM-LSS survey: optical assessment and properties of different X-ray selected cluster classes

Context. XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with previous missions. Aims. This article presents 66 spectroscopically confirmed clusters (0.05 textless= z textless= 1.5) within an area of 6 deg(2) enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Methods. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Results. Most of these objects are low-mass clusters, hence constituting a still poorly studied population. In a second step, we quantify the correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar compact structures in the surveyed area such as very distant clusters and fossil groups.

The XMM Large-Scale Structure survey: a well-controlled X-ray cluster sample over the D1 CFHTLS area

We present the XMM Large-Scale Structure Survey (XMM-LSS) cluster catalogue corresponding to the Canada-France-Hawaii Telescope Legacy Survey Dl area. The list contains 13 spectroscopically confirmed, X-ray selected galaxy clusters over 0.8 deg 2 to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster X-ray bolometric luminosities range from 0.03 to 5 x 10 44 erg s -1 . In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with (0.5-2.0 keV) X-ray fluxes of >2 x 10 -14 erg s -1 cm -2 than we expected based on expectations from deep ROSAT surveys. We also present the luminosity-temperature relation for our nine brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z < 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster data base.

The XMM-Large scale structure catalogue: X-ray sources and associated optical data. Version I

Following the presentation of the XMM-Large Scale Structure (XMM-LSS) survey X-ray source detection package by Pacaud et al., we provide the source lists for the first surveyed 5.5 deg 2 . The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain in total 3385 point-like or extended sources above a detection likelihood of 15 in either band. The agreement with deep log N- log S is excellent. The main parameters considered are position, count rate, source extent with associated likelihood values. A set of additional quantities such as astrometric corrections and fluxes are further calculated while errors on the position and count rate are deduced from simulations. We describe the construction of the band-merged catalogue allowing rapid subsample selection and easy cross-correlation with external multiwavelength catalogues. A small optical Canada-France-Hawaii Telescope Legacy Survey multiband subset of objects are associated with each source along with an X-ray/optical overlay. We make the full X-ray images available in FITS format. The data are available at the Centre de Donnees de Strasbourg and, in a more extended form, at the Milan XMM-LSS survey data base.

The XMM-LSS survey - The XMDS/VVDS 4 sigma catalogue

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and used to derive a well defined catalogue of X-ray sources. The present catalogue is limited to a sub-sample of 286 sources detected at 4σ in the 1 deg 2 area covered by the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide optical and radio identifications. We also discuss the X-ray properties of a larger X-ray sample of 536 sources detected at >4σ in the full 3 deg 2 area of the XMM Medium Deep Survey (XMDS) independently of the optical identification. We also derive the log N - log S relationship for a sample of more than one thousand sources that we discuss in the context of other surveys at similar fluxes.