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تسجيل مستخدم جديدThe XMM-Newton/2dF survey - V. the radio properties of the X-ray population
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In this paper we cross-correlate the FIRST 1.4GHz radio survey with a wide field (~ 1.6deg^2) shallow [f(0.5-8keV) ~ 1e-14erg/s/cm^2] XMM-Newton survey. We find 12 X-ray/radio matches representing 4% of the X-ray selected sample. Most of them are found to be associated with AGNs (total of 9) on the basis of the observed optical spectra (3), radio morphology (2) or X-ray/optical properties (4), while one radio source is identified with an X-ray selected cluster. We also find two sources associated with low redshift galaxies with narrow emission line optical spectra, X-ray luminosity L(0.5-8keV) ~ 1e41erg/s, radio luminosity density L(1.4GHz) ~ 5e22W/Hz and logf_X/f_{opt} ~ -2 suggesting `normal star-forming galaxies. We argue that radio surveys combined with X-ray sample could provide a powerful tool for identifying X-ray selected `normal galaxies powered by stellar processes. Finally, radio loud and quiet systems in the present sample have mean X-ray spectral properties consistent with Gamma ~ 1.9.
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This paper explores the X-ray properties of `normal galaxies using a shallow XMM-Newton survey covering an area of ~1.5deg2. The X-ray survey overlaps with the 2dF Galaxy Redshift Survey. Compared with previous studies this has the advantage of high
quality spectra and spectral classifications to bj=19.4. Moreover, sources with optical spectra revealing powerful AGNs can easily be discarded from the normal galaxy sample used here. In particular, we present stacking analysis results for 200 galaxies from the 2dFGRS at <z>=0.1. We detect a strong signal for the whole sample (~6sigma) in the soft 0.5-2keV band corresponding to a flux of ~7*10^-16cgs and a luminosity of ~2*10^40cgs. A statistically significant signal is also detected for both the early and late galaxy sub-samples with X-ray luminosities of ~3*10^40 and ~5*10^39cgs respectively. In contrast, no signal is detected in the hard 2-8keV band for any of the above samples. The mean L_X/L_B ratio of the spiral galaxy sample is consistent with both local (<100Mpc) and distant (z~1) samples suggesting little or no evolution of the X-ray emission mechanisms relative to the optical. The 0.5-2keV XRB contribution of the spiral galaxy sub-sample at z~0.1 is estimated to be 0.4% in broad agreement with the XRB fractions estimated in previous studies.Assuming that star-forming galaxies evolve with redshift as (1+z)^{k} the present data combined with previous studies suggest k<3. The k values are constrained by the relatively low fraction of the soft X-ray background that remains unresolved by deep surveys (6-26%). The mean X-ray emissivity of spiral galaxies at z~0.1 is also estimated and is found to be consistent within the uncertainties with that of local HII galaxy samples.
In this paper we investigate the properties of low X-ray-to-optical flux ratio sources detected in a wide area (2.5deg^2) shallow (f(0.5-8keV)~10e-14cgs) XMM-Newton survey. We find a total of 26 sources (5% of the total X-ray selected population) wit
h log f_X/f_{opt}<-0.9 to the above flux limit. Optical spectroscopy is available for 20 of these low X-ray-to-optical flux ratio objects. Most of them are found to be associated with Galactic stars (total of 8) and broad line AGNs (total of 8).We also find two sources with optical spectra showing absorption and/or narrow emission lines and X-ray/optical properties suggesting AGN activity. Another two sources are found to be associated with low redshift galaxies with narrow emission line optical spectra, X-ray luminosities L_X(0.5-8keV)~10e41cgs and logf_X/f_opt ~ -2 suggesting `normal star-forming galaxies. Despite the small number statistics the sky density of `normal X-ray selected star-forming galaxies at the flux limit of the present sample is low consistent with previous ROSAT HRI deep surveys. Also, the number density estimated here is in good agreement with both the logN-logS of `normal galaxies in the Chandra Deep Field North (extrapolated to bright fluxes) and model predictions based on the X-ray luminosity function of local star-forming galaxies.
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.
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 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~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 .
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. We report on the optical identification of the XMS samples, complete to 85-95%. At the intermediate 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 (~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.
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