Active and Passive Galaxies in ROSAT Deep Surveys

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Session 22 -- ROSAT
Oral presentation, Wednesday, January 12, 10:15-11:45, Salon III Room (Crystal Gateway)

[22.02] Active and Passive Galaxies in ROSAT Deep Surveys

R. E. Griffiths (Johns Hopkins University)

We have performed $\sim 30$ ks surveys of 5 fields which had previously been surveyed for UV-excess quasars by Boyle et al (1990). We have secured optical identifications for $\sim 75\%$ of the 215 sources in the sample, using multi-object spectrographs at the AAT. The AGN content of the first two of these fields (see Shanks et al 1991) has been described by Boyle et al (1993), who calculate the AGN luminosity function and the constraints on its evolution. AGN account for up to 70\% of the X-ray background between 1 and 2 keV. In this talk, we focus on the non-AGN counterparts to the deep survey sources, and describe the galaxy content of the identifications, both early-type and emission-line galaxies.

The ten early-type (E to Sab) galaxies have X-ray luminosities of up to $\sim 10^{43}$ ergs s$^{-1}$, but show no optical signatures indicative of such large X-ray luminosities. We explore various hypotheses for the origin of this emission, including bremmstrahlung from coronal gas contrained by dark matter surrounding the ellipticals.

The sixteen narrow emission-line (NL) galaxies have optical spectra typical of ``starburst'' galaxies, although we cannot generally rule out the presence of Seyfert 2 nuclei. We derive a luminosity function (LF) for the X-ray selected NL galaxies and compare it with the local X-ray LF of the AGN in the EMSS. We estimate the contribution to the 1 -- 2 kev X-ray background from these galaxies, on the assumptions of (i) no evolution, and (ii) evolution similar to that of AGN.

References: Shanks et al., 1991, Nature 353 , 315.

Boyle, B, J., et al., 1993, MNRAS, 260 , 49.

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