Searching for X-ray luminous 'normal' galaxies in 2dfGRS
Abstract
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 (LX > 1042 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 log(fX/fO) < -2 for separating AGN from NGs. With XMM-Newton (Chandra) we covered an area of ~8.2 (~5.8)deg2 down to a flux limit of ~10-15 (~1.6 x 10-15) erg cm-2 s-1 and found 18 (20) 2dfGRS galaxies. Using emission-line intensity ratios, we classified 6 2dfGRS spectra as star-forming, H II nuclei, and 2 spectra as possible H II 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 H II and 3 absorption-line galaxies have log(fX/fO) > -2. We performed a similar search in two nearby-galaxy samples from the literature. All 44 galaxies in the Zezas (2001) sample have log(fX/fO) < -2 and LX < 1042 erg s-1. In the Fabbiano et al. (1992) sample, out of a total of 170 'normal' galaxies, we found 16 galaxies with log(fX/fO) >-2, the majority of which are massive ellipticals. Three of these have LX > 1042 erg s-1 .
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