Searching for X-ray luminous “normal” galaxies in 2dFGRS
Institute of Astronomy & Astrophysics, National Observatory of Athens, I. Metaxa & V. Pavlou, Penteli 15236, Greece e-mail: email@example.com
2 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Rd., London, SW7 2AW, UK
Accepted: 26 February 2006
Aims.We cross-correlated the Chandra XASSIST and XMM-Newton Serendipitous Source Catalogues with the 2 degree Field Galaxy Redshift Survey (2dFGRS) database. Our aim was to identify the most X-ray luminous ( erg s-1) examples of galaxies in the local Universe whose X-ray emission is dominated by stellar processes rather than AGN activity (“normal” galaxies), as well as to test the empirical criterion for separating AGN from NGs. We also performed a similar search in two nearby-galaxy samples from the literature.
Methods.With XMM-Newton (Chandra) we covered an area of ∼8.2 (5.8) deg2 down to a flux limit of () erg cm-2 s-1. We classified 2dFGRS spectra using emission-line intensity ratios.
Results.We found 18 (20) 2dFGRS galaxies with XMM-Newton (Chandra), which constitute our XMM-Newton-2dFGRS (Chandra-2dFGRS) correlation sample. We classified 6 2dFGRS spectra as star-forming, nuclei, and 2 spectra as possible nuclei. The rest of the objects are absorption-line galaxies and AGN, including 3 possible LINERs. No luminous “normal” galaxies have been found, but out of 19 “normal” galaxies in this sample, 5 and 3 absorption-line galaxies have . Furthermore, all 44 galaxies in the first literature sample have and erg s-1. In the second literature sample, out of a total of 170 “normal” galaxies, we found 16 galaxies with , the majority of which are massive ellipticals. Three of these have erg s-1.
Conclusions.We found no luminous “normal” galaxies in our XMM-Newton-2dFGRS and Chandra-2dFGRS correlation samples. We found three such galaxies in the second literature sample. Considering all samples, we find that the criterion seems to select primarily against the brightest, massive ellipticals.
Key words: X-rays: galaxies / galaxies: starburst / galaxies: active
© ESO, 2006