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Register a new userAn X-ray Survey in SA 57 with XMM-Newton
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The maximum number density of Active Galactic Nuclei (AGNs), as deduced from X-ray studies, occurs at z<~1, with lower luminosity objects peaking at smaller redshifts. Optical studies lead to a different evolutionary behaviour, with a number density peaking at z~2 independently of the intrinsic luminosity, but this result is limited to active nuclei brighter than the host galaxy. A selection based on optical variability can detect low luminosity AGNs (LLAGNs), where the host galaxy light prevents the identification by non-stellar colours. We want to collect X-ray data in a field where it exists an optically-selected sample of variable galaxies, i.e. variable objects with diffuse appearance, to investigate the X-ray and optical properties of the population of AGNs, particularly of low luminosity ones, where the host galaxy is visible. We observed a field of 0.2 deg^2 in the Selected Area 57, for 67ks with XMM-Newton. We detected X-ray sources, and we correlated the list with a photographic survey of SA 57, complete to B_J~23 and with available spectroscopic data. We obtained a catalogue of 140 X-ray sources to limiting fluxes 5x10^-16, 2x10^-15 erg/cm^2/s in the 0.5-2 keV and 2-10 keV respectively, 98 of which are identified in the optical bands. The X-ray detection of part of the variability-selected candidates confirms their AGN nature. Diffuse variable objects populate the low luminosity side of the sample. Only 25/44 optically-selected QSOs are detected in X-rays. 15% of all QSOs in the field have X/O<0.1.
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We report the details of an XMM observation of the cluster of galaxies ZW 1305.4+2941 at the intermediate redshift of z=0.241, increasing the small number of interesting X-ray constraints on properties of ~3 keV systems above z=0.1. Based on the 45 ks XMM observation, we find that within a radius of 228 kpc the cluster has an unabsorbed X-ray flux of 2.07 +/- 0.06 x 10^{-13} erg/cm^2/s, a temperature of kT = 3.17 +/-0.19 keV, in good agreement with the previous ROSAT determination, and an abundance of 0.93 (+0.24,-0.29} solar. Within r_500 = 723 +/- 6 kpc the rest-frame bolometric X-ray luminosity is L_X (r_500)= 1.25 +/- 0.16 x 10^{44} erg/s. The cluster obeys the scaling relations for L_X, T and the velocity dispersion derived at intermediate redshift for kT < 4 keV, for which we provide new fits for all literature objects. The mass derived from an isothermal NFW model fit is, M_vir = 2.77 +/- 0.21 x 10^{14} solar masses, with a concentration parameter, c = 7.9 +/- 0.5.
XMM-Newton observations of 10 ULIRGs are reported. The aim is to investigate in hard X-rays a complete ULIRG sample selected from the bright IRAS 60$mu$m catalogue. All sources are detected in X-rays, 5 of which for the first time. These observations confirm that ULIRGs are intrinsically faint X-rays sources, their observed X-ray luminosities being typically L(2-10 keV)<1E42-43 erg/s, whereas their bolometric luminosities are L>1E45 erg/s. In all sources we find evidence for thermal emission from hot plasma with kT~0.7keV, dominating the X-ray spectra below 1keV, and likely associated with a nuclear or circumnuclear starburst. This thermal emission appears uncorrelated with the FIR luminosity, suggesting that,in addition to the ongoing rate of star formation, other parameters may also affect it. The soft X-ray emission appears to be extended on a scale of ~30kpc for Mkn231 and IRAS19254-7245, possible evidence of galactic superwinds. In these 2 sources, in IRAS20551-4250 and IRAS23128-5919 we find evidence for the presence of hidden AGNs, while a minor AGN contribution may be suspected also in IRAS20100-4156. In particular, we have detected a strong Fe line at 6.4keV in the spectrum of IRAS19254-7245 and a weaker one in Mkn231, suggestive of deeply buried AGNs. For the other sources, the X-ray luminosities and spectral shapes are consistent with hot thermal plasma and X-ray binary emissions of mainly starburst origin. We find that the 2-10keV luminosities in these sources, most likely due to high-mass X-ray binaries, are correlated with L_FIR: both luminosities are good indicators of the current global SFR in the galaxy. The composite nature of ULIRGs is then confirmed, with hints for a predominance of the starburst over the AGN phenomenon in these objects.
We present measurements of the Galactic halos X-ray emission for 110 XMM-Newton sight lines, selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on ~4/5 of our sight lines. The temperature is fairly uniform (median = 2.22e6 K, interquartile range = 0.63e6 K), while the emission measure and intrinsic 0.5--2.0 keV surface brightness vary by over an order of magnitude (~(0.4-7)e-3 cm^-6 pc and ~(0.5-7)e-12 erg cm^-2 s^-1 deg^-2, respectively, with median detections of 1.9e-3 cm^-6 pc and 1.5e-12 erg cm^-2 s^-1 deg^-2, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.
We briefly report on an on-going spectroscopic study of hard X-ray sources selected serendipitously in 12 XMM-Newton fields. Results for the analysis of the 41 sources from the first seven EPIC observations have been discussed in a previous paper (Piconcelli et al. 2002, Paper I) where we found an absolute fraction of X-ray absorbed sources (~30%) lower than expected (~50%) by the predictions of popular CXB synthesis models at F(2-10)~5x10**(-14) erg cm**-2 s**-1. We present here the preliminary results concerning the whole sample including five new deeper XMM-Newton measurements increasing the sample to 90 sources. Even if still on-going, the present study appears to confirm and extend down to F(2-10)~10**(-14) erg cm**-2 s**-1 the above mismatch between observational data and theoretical expectations regarding the fraction of absorbed sources. Furthermore the sample average spectral index of 1.5-1.6 is steeper than the CXB slope indicating that the majority of obscured sources making the bulk of the CXB resides at even lower hard X-ray fluxes.
We present the X-ray source catalog in the Subaru/XMM-Newton deep survey. A continuous area of 1.14 deg^2 centered at R.A. = 02h18m and Dec. = -05d is mapped by seven pointings with XMM-Newton covering the 0.2-10 keV band. From the combined images of the EPIC pn and MOS cameras, we detect 866, 1114, 645, and 136 sources with sensitivity limits of 6x10^{-16}, 8x10^{-16}, 3x10^{-15}, and 5x10^{-15} erg cm^{-2} s^{-1} in the 0.5-2, 0.5-4.5, 2-10, and 4.5-10 keV bands, respectively, with detection likelihood >= 7 (corresponding to a confidence level of 99.91%). The catalog consists of 1245 sources in total including 32 extended-source candidates. The averaged log N-log S relations are in good agreement with previous results, bridging the flux range between Chandra deep surveys and brighter surveys. The log N-log S relations show significant spatial variation among pointings on a scale of 0.2 deg^2. Analyzing the auto correlation function, we detect significant clustering signals from the 0.5-2 keV band sample, which can be fit with a power law form (theta/theta_c)^{-0.8} with a correlation length of theta_c=5.9^{+1.0}_{-0.9} arcsec when the integral constraint term is included. In the 2-10 keV band, however, the clustering is not significant with a 90% upper limit of theta_c < 1.5 arcsec.
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