An X-ray survey of galaxies in Pairs

Results are reported from the first survey of X-ray emission from galaxies in pairs. The sample consists of 52 pairs of galaxies from the Catalog of P aired Galaxies whose coordinates overlap the ROSAT Position Sensitive Propo rtional Counter pointed observations. The mean observed log l(x) for early- type pairsis 41.35 +/- 0.21, while the mean log l(x) predicted using the l( x)-l(b) relationship for isolated early-type galaxies is 42.10 +/- 0.19. Wi th 95% confidence, the galaxies in pairs are underluminous in the X-ray, co mpared with isolated galaxies, for the same l(b). A significant fraction of the mixed pair sample also appears similarly underluminous. A spatial anal ysis shows that the X-ray emission from pairs of both types typically has a n extent of similar to 10-50 kpc, much smaller than the group intergalactic medium, and thus likely originates from the galaxies. CPG 564, the most X- ray luminous early-type pair, 4.7 x 10(42) ergs s(-1), is an exception. The extent of its X-ray emission, greater than 169 kpc, and HWHM, similar to 8 0 kpc, is comparable to that expected from an intergalactic medium. The sam ple shows only a weak correlation, similar to 81% confidence, between l(x) and l(b), presumably due to variations in gas content within the galaxies. No correlation between l(x) and the pair velocity difference (Delta v), sep aration (Delta r), or far-infrared luminosity (l(fir)) is found, although t he detection rate is low, 22%.