OVI observations of galaxy clusters: Evidence for modest cooling flows

A prediction of the galaxy-cluster cooling flow model is that as gas cools from the ambient cluster temperature, emission lines are produced in gas at subsequently decreasing temperatures. Gas passing through 10(5.5) K emits in the lines of O (VI) lambda lambda 1032, 1035, and here we report a FUSE study of these lines in three cooling flow clusters, Abell 426, Abell 1795, and AWM 7. No emission was detected from AWM 7, but O vi is detected from the centers of Abell 426 and Abell 1795, and possibly to the south of the center in Abell 1795, where X-ray and optical emission line filaments lie. In Abell 426 these line luminosities imply a cooling rate of 32 +/- 6M(circle dot) yr(-1) within the central r = 6.2 kpc region, while for Abell 1795 the central cooling rate is 26 +/- 7 M-circle dot yr(-1) (within r = 22 kpc), and about 42 +/- 9 M-circle dot yr(-1) including the southern pointing. Including other studies, three of six clusters have O vi emission, and they also have star formation as well as emission lines from 104 K gas. These observations are generally consistent with the cooling flow model, but at a rate closer to 30 M-circle dot yr(-1) than to the originally suggested values of 10(2)-10(3) M-circle dot yr(1).