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Register a new userThe XMM-Newton/2dF survey I: X-ray properties of normal galaxies
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Antonis Georgakakis
Publication date
2003
fields
Physics
and research's language is
English
Authors
A. Georgakakis
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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.
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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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The technique of estimating redshifts using photometric rather than spectroscopic observations has recently received great attention due to its simplicity and the accuracy of the results obtained. In this work, we estimate photometric redshifts for an X-ray selected QSO sample. This is the first time this technique is applied on such a sample. We first calculate the accuracy of the results obtained by comparing photometric to spectroscopic redshifts for a sub-sample of our QSO sample: for the majority (~67%) of the objects in this sub-sample, photometric redshift estimates are correct within Dz<0.3. We then derive the photometric redshift distribution for the whole QSO sample. In the future, we expect to use the photometric redshift distribution in order to derive the distributions of properties such as the Hardness Ratio and hence the hydrogen column density, the luminosity function etc. As an example, we estimate here the dependence of the Hardness Ratio of the QSO sample on photometric redshift.
This paper describes the performance of XMM-Newton for serendipitous surveys and summarises the scope and potential of the XMM-Newton Serendipitous Survey. The role of the Survey Science Centre (SSC) in the XMM-Newton project is outlined. The SSCs follow-up and identification programme for the XMM-Newton serendipitous survey is described together with the presentation of some of the first results.
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