X. Barcons

The XMM-Newton serendipitous survey: V - The Second XMM-Newton serendipitous source catalogue

Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods. The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results. The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg(2). The non-overlapping sky area is similar to 360 deg(2) (similar to 1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties

XMM-Newton observation of the Lockman hole: I. the x-ray data

We report on the first deep X-ray survey with the XMM-Newton observatory during the performance verification phase. The field of the Lockman Hole, one of the best studied sky areas over a very wide range of wavelengths, has been observed. A total of ~100 ksec good exposure time has been accumulated. Combining the images of the European Photon Imaging Camera (EPIC) detectors we reach a flux limit of 0.31, 1.4 and

Using the Bright Ultrahard XMM–Newton survey to define an IR selection of luminous AGN based on WISE colours

2.4 10^{-15} {\rm erg} {\rm cm}^{-2} {\rm s}^{-1}

The Gaseous Extent of Galaxies and the Origin of Lyα Absorption Systems. V. Optical and Near-Infrared Photometry of Lyα-absorbing Galaxies at z < 1*

, respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of 10 arcmin we detect 148, 112 and 61 sources, respectively. The log( N )-log( S ) relation in the three bands is compared with previous results. In particular in the 5-10 keV band these observations present the deepest X-ray survey ever, about a factor 20 more sensitive than the previous BeppoSAX observations. Using X-ray spectral diagnostics and the set of previously known, spectroscopically identified ROSAT sources in the field, the new sources can be classified. XMM-Newton detects a significant number (~40% ) of X-ray sources with hard, probably intrinsically absorbed X-ray spectra, confirming a prediction of the population synthesis models for the X-ray background.

The XMM Deep survey in the CDF-S - I. First results on heavily obscured AGN

We present a highly complete and reliable mid-infrared (MIR) colour selection of luminous active galactic nucleus (AGN) candidates using the 3.4, 4.6 and 12 µm bands of the Widefield Infrared Survey Explorer (WISE) survey. The MIR colour wedge was defined using the wide-angle Bright Ultrahard XMM–Newton survey (BUXS), one of the largest complete flux-limited samples of bright (f4.5–10 keV > 6 × 10 −14 erg s −1 cm −2 ) ‘ultrahard’ (4.5–10 keV) X-ray-selected AGN to date. The BUXS includes 258 objects detected over a total sky area of 44.43 deg 2 of which 251 are spectroscopically identified and classified, with 145 being type 1 AGN and 106 type 2 AGN. Our technique is designed to select objects with red MIR power-law spectral energy distributions (SEDs) in the three shortest bands of WISE and properly accounts for the errors in the photometry and deviations of the MIR SEDs from a pure power-law. The completeness of the MIR selection is a strong function of luminosity. At L2–10 keV > 10 44 erg s −1 , where the AGN is expected to dominate the MIR emission, 97.1 +2.2 −4.8 and 76.5 +13.3 per cent of the BUXS type 1 and type 2 AGN, respectively, meet the selection. Our technique shows one of the highest reliability and efficiency of detection of the X-rayselected luminous AGN population with WISE amongst those in the literature. In the area covered by BUXS our selection identifies 2755 AGN candidates detected with signal-to-noise ratio ≥5 in the three shorter wavelength bands of WISE with 38.5 per cent having a detection at 2–10 keV X-ray energies. We also analysed the possibility of including the 22µm WISE band to select AGN candidates, but neither the completeness nor the reliability of the selection improves. This is likely due to both the significantly shallower depth at 22µm compared with the first three bands of WISE and star formation contributing to the 22µm emission at the WISE 22µm sensitivity.

The Gaseous Extent of Galaxies and the Origin of Ly? Absorption Systems. III. Hubble Space Telescope Imaging of Ly?-absorbing Galaxies at z < 1

We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Considering a sample of physically correlated galaxy and absorber pairs with galaxy-absorber cross-correlation amplitude ξga(v,ρ) > 1 and with galaxy impact parameter ρ < 200 h-1 kpc, we confirm and improve the results presented by Lanzetta et al. and Chen et al. that (1) extended gaseous envelopes are a common and generic feature of galaxies of a wide range of luminosity and morphological type, (2) the extent of tenuous gas [N(H ) 1014 cm-2] around galaxies scales with galaxy B-band luminosity as r ∝ L, and (3) galaxy interactions do not play an important role in distributing tenuous gas around galaxies in most cases. We further demonstrate that (4) the gaseous extent of galaxies scales with galaxy K-band luminosity as r ∝ L, and (5) tenuous gas around typical L* galaxies is likely to be distributed in spherical halos of radius ≈180 h-1 kpc of covering factor of nearly unity. The sample consists of 34 galaxy and absorber pairs and 13 galaxies that do not produce Lyα absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs range from z = 0.0752 to 0.8920 with a median of z = 0.3567; impact parameter separations of the galaxy and absorber pairs range from ρ = 12.4 to 175.2 h-1 kpc with a median of ρ = 62.2 h-1 kpc. Of the galaxies, 15 (32%) are of B-band luminosity LB < 0.25 L and six (13%) are of low surface brightness. The galaxy sample is therefore representative of the galaxy population over a large fraction of the Hubble time. Because galaxies of all morphological types possess extended gaseous halos and because the extent of tenuous gas around galaxies scales with galaxy K-band luminosity, we argue that galaxy mass—rather than recent star formation activity—is likely to be the dominant factor that determines the extent of tenuous gas around galaxies. Nevertheless, applying the scaling relationship between the extent of Lyα-absorbing gas around galaxies and galaxy B-band luminosity, the results of our analysis also suggest that the number density evolution of Lyα absorption systems may serve to constrain the evolution of the comoving galaxy B-band luminosity density (at least for the redshift interval between z ~ 0 and z ~ 1 that has been studied in our survey).

The XMM-Newton serendipitous survey - IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)

We present the first results of the spectroscopy of distant, o bscured AGN as obtained with the ultra‐deep (�3.3 Ms) XMM‐Newton survey in the Chandra Deep Field South (CDF‐S). One of the primary goals of the project is to characterize the X‐ray spectral properties of obscured and heavily obscured Compton‐thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X‐ray background. The ultra‐deep exposure, coupled with the XMM detector’s spectral throughput, allowed us to accumulate good quality X‐ray spectra for a large number of X‐ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X ‐ray spectral properties of two high‐redshift ‐ z= 1.53 and z=3.70 ‐

The X-ray and radio connection in low-luminosity active nuclei

We present initial results of a program to obtain and analyze Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. We measure properties of 87 galaxies, of which 33 are associated with corresponding Ly? absorption systems and 24 do not produce corresponding Ly? absorption lines to within sensitive upper limits. Considering only galaxy and absorber pairs that are likely to be physically associated and excluding galaxy and absorber pairs within 3000 km s-1 of the background QSOs leaves 26 galaxy and absorber pairs and seven galaxies that do not produce corresponding Ly? absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs range from 0.0750 to 0.8912 with a median of 0.3718, and impact parameter separations of the galaxy and absorber pairs range from 12.4 to 157.4 h-1 kpc with a median of 62.4 h-1 kpc. The primary result of the analysis is that the amount of gas encountered along the line of sight depends on the galaxy impact parameter and B-band luminosity but does not depend strongly on the galaxy average surface brightness, disk-to-bulge ratio, or redshift. This result confirms and improves upon the anticorrelation between Ly? absorption equivalent width and galaxy impact parameter found previously by Lanzetta et al. in 1995. Spherical halos cannot be distinguished from flattened disks on the basis of the current observations, and there is no evidence that galaxy interactions play an important role in distributing tenuous gas around galaxies in most cases. Galaxies might account for all Ly? absorption systems with W > 0.3 ?, but this depends on the unknown luminosity function and gaseous cross sections of low-luminosity galaxies as well as on the uncertainties of the observed number density of Ly? absorption systems.

XMM-Newton observations reveal AGN in apparently normal galaxies

Aims. X-ray sources at intermediate fluxes (a few x 10(-14) erg cm(-2) s(-1)) with a sky density of similar to 100 deg(-2) are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods. We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. Results. We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (similar to 35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.

Do nuclear starbursts obscure the X-ray background?

We present the results of the correlation between the nuclear 2–10 keV X-ray and radio (at 2 cm, 6 cm, and 20 cm) luminosities for a well-defined sample of local Seyfert galaxies. We use a sample of low luminosity radio galaxies (LLRGs) for comparison. In both Seyfert and LLRG samples, X-ray and radio luminosities are significantly correlated over 8 orders of magnitude, indicating that the X-ray and radio emission sources are strongly coupled. Moreover, both samples show a similar regression slope, LX ∝ L 0.97 R , but Seyfert galaxies are three orders of magnitude less luminous in the radio band than LLRGs. This suggests that either similar physical mechanisms are responsible for the observed emission or a combination of different mechanisms ends up producing a similar correlation slope. Indeed, the common belief for LLRG is that both the X-ray and radio emission are likely dominated by a relativistic jet component, while in Seyfert galaxies the X-ray emission probably arises from a disk-corona system and the radio emission is attributed to a jet/outflow component. We investigate the radio loudness issue in the two samples and find that the Seyfert galaxies and the LLRGs show a different distribution of the radio loudness parameters. No correlation is found between the luminosity and the radio loudness; however, the latter is related to the black hole mass and anti-correlated with the Eddington ratio. The dichotomy in the radio loudness between Seyfert and LLRG observed down to low Eddington ratios, L2−10 keV/LEdd ∼ 10 −8 , does not support the idea that the origin of the radio loudness is due to a switch in the accretion mode.