Dark X-Ray Galaxies in the A1367 Galaxy Cluster

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.