OviObservations 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 λλ1032, 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 ± 6 M ☉ yr -1 within the central r = 6.2 kpc region, while for Abell 1795 the central cooling rate is 26 ± 7 M ☉ yr -1 (within r = 22 kpc), and about 42 ± 9 M ☉ 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 10 4 K gas. These observations are generally consistent with the cooling flow model, but at a rate closer to 30 M ☉ yr -1 than to the originally suggested values of 10 2 -10 3 M ☉ yr -1 .