Dark X-Ray Galaxies in the A1367 Galaxy Cluster

Abstract

We have characterized a sample of extended X-ray sources in the A1367 galaxy cluster that lack optical counterparts. The sources are galaxy size and have an average total mass of 1.3 × 10¹¹ solar masses. The average hot gas mass is 3.0 × 10⁹ solar masses and the average X-ray luminosity is 4.3 × 10⁴¹ erg cm^-2 s^-1. Analysis of a composite source spectrum indicates the X-ray emission is thermal, with temperature of 1.25-1.45 keV and has low metallicity, 0.026-0.067 solar. The average hot gas radius (12.7 kpc) is well matched to nominal stripping radius. We argue that this optically dark, X-ray bright galaxy population forms by a sequence of stripping followed by heating and mixing with the intracluster medium.