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 Paired Galaxies whose coordinates overlap the ROSAT Position Sensitive Proportional 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. With 95% confidence, the galaxies in pairs are underluminous in the X-ray, compared with isolated galaxies, for the same l_b. A significant fraction of the mixed pair sample also appears similarly underluminous. A spatial analysis shows that the X-ray emission from pairs of both types typically has an extent of ∼ 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 × 10⁴² ergs s^-1, is an exception. The extent of its X-ray emission, greater than 169 kpc, and HWHM, ∼80 kpc, is comparable to that expected from an intergalactic medium. The sample shows only a weak correlation, ∼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 (Δv), separation (Δr), or far-infrared luminosity (l_fir) is found, although the detection rate is low, 22%.