Nature of “passive” elliptical galaxies

We present ROSAT HRI images of three candidate “passive” elliptical galaxies from the Einstein EMSS. Passive Es are the third most abundant identification type in deep ROSAT surveys (e.g., Griffiths et al. 1995) and could be major contributors to the XRB if they have hard X-ray spectra from an AGN. Deep-survey passive Es are too faint and too distant to address the question of their nature with the ROSAT HRI. Therefore, we have imaged three nearby, unusually X-ray luminous elliptical galaxies from the EMSS to determine whether they have weak AGN and are thus potential contributors to the XRB; or if they are diffuse, hot gas emitters, in which case they add significantly to the dark matter content of the Universe. No evidence is found for a significant AGN contribution to the X-ray flux in any of these objects, suggesting that passive ellipticals are not significant contributors to the hard XRB.