Wide area X-ray and far infrared surveys are a fundamental tool to investigate the link between AGN growth and star formation, especially in the low-redshift universe (z<1). The Herschel Terahertz Large Area survey (H-ATLAS) has covered 550 deg^2 in
five far-infrared and sub-mm bands, 16 deg^2 of which have been presented in the Science Demonstration Phase (SDP) catalogue. Here we introduce the XMM-Newton observations in H-ATLAS SDP area, covering 7.1 deg^2 with flux limits of 2e-15, 6e-15 and 9e-15 erg/s/cm^2 in the 0.5--2, 0.5--8 and 2--8 keV bands, respectively. We present the source detection and the catalogue, which includes 1700, 1582 and 814 sources detected by Emldetect in the 0.5--8, 0.5--2 and 2--8 keV bands, respectively; the number of unique sources is 1816. We extract spectra and derive fluxes from power-law fits for 398 sources with more than 40 counts in the 0.5--8 keV band. We compare the best-fit fluxes with the catalogue ones, obtained by assuming a common photon index of Gamma=1.7; we find no bulk difference between the fluxes, and a moderate dispersion of s=0.33 dex. Using wherever possible the fluxes from the spectral fits, we derive the 2--10 keV LogN-LogS, which is consistent with a Euclidean distribution. Finally, we release computer code for the tools developed for this project.
The XMM-Newton spectral-fit database (XMMFITCAT) is a catalogue of spectral fitting results for the source detections within the XMM-Newton Serendipitous source catalogue with more than 50 net (background-subtracted) counts per detector in the 0.5-10
keV energy band. Its most recent version, constructed from the latest version of the XMM-Newton catalogue, the 3XMM Data Release 4 (3XMM-DR4), contains spectral-fitting results for $gtrsim$ 114,000 detections, corresponding to $simeq$ 78,000 unique sources. Three energy bands are defined and used in the construction of XMMFITCAT: Soft (0.5-2 keV), Hard (2-10 keV), and Full (0.5-10 keV) bands. Six spectral models, three simple and three more complex models, were implemented and applied to the spectral data. Simple models are applied to all sources, whereas complex models are applied to observations with more than 500 counts (30%). XMMFITCAT includes best-fit parameters and errors, fluxes, and goodness of fit estimates for all fitted models. XMMFITCAT has been conceived to provide the astronomical community with a tool to construct large and representative samples of X-ray sources by allowing source selection according to spectral properties, as well as characterise the X-ray properties of samples selected in different wavelengths. We present in this paper the main details of the construction of this database, and summarise its main characteristics.
The majority of active galactic nuclei (AGN) are obscured by large amounts of absorbing material that makes them invisible at many wavelengths. X-rays, given their penetrating power, provide the most secure way for finding these AGN. The XMM-Newton s
erendipitous source catalog is the largest catalog of X-ray sources ever produced; it contains about half a million detections. These sources are mostly AGN. We have derived X-ray spectral fits for very many 3XMM-DR4 sources ($gtrsim$ 114 000 observations, corresponding to $sim$ 77 000 unique sources), which contain more than 50 source photons per detector. Here, we use a subsample of $simeq$ 1000 AGN in the footprint of the SDSS area (covering 120 deg$^2$) with available spectroscopic redshifts. We searched for highly obscured AGN by applying an automated selection technique based on X-ray spectral analysis that is capable of efficiently selecting AGN. The selection is based on the presence of either a) flat rest-frame spectra; b) flat observed spectra; c) an absorption turnover, indicative of a high rest-frame column density; or d) an Fe K$alpha$ line with an equivalent width > 500 eV. We found 81 highly obscured candidate sources. Subsequent detailed manual spectral fits revealed that 28 of them are heavily absorbed by column densities higher than 10$^{23}$ cm$^{-2}$. Of these 28 AGN, 15 are candidate Compton-thick AGN on the basis of either a high column density, consistent within the 90% confidence level with N$_{rm H}$ $>$10$^{24}$ cm$^{-2}$, or a large equivalent width (>500 eV) of the Fe K$alpha$ line. Another six are associated with near-Compton-thick AGN with column densities of $sim$ 5$times$10$^{23}$ cm$^{-2}$. A combination of selection criteria a) and c) for low-quality spectra, and a) and d) for medium- to high-quality spectra, pinpoint highly absorbed AGN with an efficiency of 80%.
The XMM-Newton spectral-fit database is an ongoing ESA funded project aimed to construct a catalogue of spectral-fitting results for all the sources within the XMM-Newton serendipitous source catalogue for which spectral data products have been pipel
ine-extracted (~ 120,000 X-ray source detections). The fundamental goal of this project is to provide the astronomical community with a tool to construct large and representative samples of X-ray sources by allowing source selection according to spectral properties.
X-ray spectroscopy of active galactic nuclei (AGN) offers the opportunity to directly probe the inner regions of the accretion disk. We present the results of our analysis of average AGN XMM-Newton X-ray spectra in the Chandra Deep Field South observ
ation (XMM CDFS). We computed the average spectrum of a sample of 54 AGN with spectroscopic redshifts and signal-to-noise ratio S/N > 15 in the 2-12 keV rest-frame band in at least one EPIC camera. We have taken the effects of combining spectra from sources at different redshifts and both EPIC cameras into account, as well as their spectral resolution; we checked our results using thorough simulations. We explored the Fe line components of distant AGN focusing on the narrow core which arises from regions far from the central engine and on the putative relativistic component (from the accretion disk). The average spectrum shows a highly significant Fe feature. Our model-independent estimates of the equivalent width (EW) suggest a higher EW in a broader range. The line, modelled as an unresolved Gaussian, is significant at 6.8 sigma and has an EW=95 eV (full sample). The current data can be fitted equally well adding a relativistic profile to the narrow component (in the full sample, EW=140 eV and 67 eV respectively for the relativistic and narrow lines). Thanks to the high quality of the XMM CDFS spectra and to the detailed modelling of the continuum and instrumental effects, we have shown that the most distant AGN exhibit a highly significant Fe emission feature. It can be modelled both with narrow and broad lines. We found tantalising evidence for reflection by material both very close and far away from the central engine. The EW of both features are similar to those observed in individual nearby AGN, hence they must be a widespread characteristic of AGN, since otherwise the average values would be smaller than observed.
The X-ray spectra of Active Galactic Nuclei (AGN) carry the signatures of the emission from the central region, close to the Super Massive Black Hole (SMBH). For this reason, the study of deep X-ray spectra is a powerful instrument to investigate the
origin of their emission. The emission line most often observed in the X-ray spectra of AGN is Fe K. It is known that it can be broadened and deformed by relativistic effects if emitted close enough to the central SMBH. In recent statistical studies of the X-ray spectra of AGN samples, it is found that a narrow Fe line is ubiquitous, while whether the broad features are as common is still uncertain. We present here the results of an investigation on the characteristics of the Fe line in the average X-ray spectra of AGN in deep Chandra fields. The average spectrum of the AGN is computed using Chandra spectra with more than 200 net counts from the AEGIS, Chandra Deep Field North and Chandra Deep Field South surveys. The sample spans a broader range of X-ray luminosities than other samples studied with stacking methods up to z=3.5. We analyze the average spectra of this sample using our own averaging method, checking the results against extensive simulations. Subsamples defined in terms of column density of the local absorber, luminosity and z are also investigated. We found a very significant Fe line with a narrow profile in all our samples and in almost all the subsamples that we constructed. The equivalent width (EW) of the narrow line estimated in the average spectrum of the full sample is 74 eV. The broad line component is significantly detected in the subsample of AGN with L<1.43 1E44 cgs and z<0.76, with EW=108 eV. We concluded that the narrow Fe line is an ubiquitous feature of the X-ray spectra of the AGN up to z=3.5.The broad line component is significant in the X-ray spectra of the AGN with low luminosity and low z.
We present here a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton bright survey (XBS) that comprises more than 300 AGN up to redshift ~ 2.4. We performed an X-ray analysis following two different approaches: by analyzing indiv
idually each AGN X-ray spectrum and by constructing average spectra for different AGN types. From the individual analysis, we find that there seems to be an anti correlation between the spectral index and the sources hard X-ray luminosity, such that the average photon index for the higher luminosity sources (> 10E44 erg/s) is significantly flatter than the average for the lower luminosity sources. We also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. We also find that the so-called soft-excess, apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe Kalpha emission line and a small (large) amount of reflection for unabsorbed (absorbed) sources. We do not significantly detect any relativistic contribution to the line emission and we compute an upper limit for its equivalent width (EW) of 230 eV at the 3 sigma confidence level. Finally, by dividing the type 1 AGN sample into high- and low-luminosity sources, we marginally detect a decrease in the narrow Fe Kalpha line EW and in the amount of reflection as the luminosity increases, the so-called Iwasawa-Taniguchi effect.
One of the most important parameters in the XRB (X-ray background) synthesis models is the average efficiency of accretion onto SMBH (super-massive black holes). This can be inferred from the shape of broad relativistic Fe lines seen in X-ray spectra
of AGN (active galactic nuclei). Several studies have tried to measure the mean Fe emission properties of AGN at different depths with very different results. We compute the mean Fe emission from a large and representative sample of AGN X-ray spectra up to redshift ~ 3.5. We developed a method of computing the rest-frame X-ray average spectrum and applied it to a large sample (more than 600 objects) of type 1 AGN from two complementary medium sensitivity surveys based on XMM-Newton data, the AXIS and XWAS samples. This method makes use of medium-to-low quality spectra without needing to fit complex models to the individual spectra but with computing a mean spectrum for the whole sample. Extensive quality tests were performed by comparing real to simulated data, and a significance for the detection of any feature over an underlying continuum was derived. We detect with a 99.9% significance an unresolved Fe K-alpha emission line around 6.4 keV with an EW ~ 90 eV, but we find no compelling evidence of any significant broad relativistic emission line in the final average spectrum. Deviations from a power law around the narrow line are best represented by a reflection component arising from cold or low-ionization material. We estimate an upper limit for the EW of any relativistic line of 400 eV at a 3 sigma confidence level. We also marginally detect the so-called Iwasawa-Taniguchi effect on the EW for the unresolved emission line, which appears weaker for higher luminosity AGN.
We present the results of the X-ray spectral analysis of an XMM-Newton-selected type II QSO sample with z>0.5 and 0.5-10 keV flux of 0.3-33 x 10^{-14} erg/s/cm^2. The distribution of absorbing column densities in type II QSOs is investigated and the
dependence of absorption on X-ray luminosity and redshift is studied. We inspected 51 spectroscopically classified type II QSO candidates from the XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS), and the AXIS survey to set-up a well-defined sample with secure optical type II identifications. Fourteen type II QSOs were classified and an X-ray spectral analysis performed. Since most of our sources have only ~40 X-ray counts (PN-detector), we carefully studied the fit results of the simulated X-ray spectra as a function of fit statistic and binning method. We determined that fitting the spectra with the Cash-statistic and a binning of minimum one count per bin recovers the input values of the simulated X-ray spectra best. Above 100 PN counts, the free fits of the spectrums slope and absorbing hydrogen column density are reliable. We find only moderate absorption (N_H=(2-10) x 10^22 cm^-2) and no obvious trends with redshift and intrinsic X-ray luminosity. In a few cases a Compton-thick absorber cannot be excluded. Two type II objects with no X-ray absorption were discovered. We find no evidence for an intrinsic separation between type II AGN and high X-ray luminosity type II QSO in terms of absorption. The stacked X-ray spectrum of our 14 type II QSOs shows no iron K-alpha line. In contrast, the stack of the 8 type II AGN reveals a very prominent iron K-alpha line at an energy of ~ 6.6 keV and an EW ~ 2 keV.
