The detection of hot intergalactic gas in the NGC 3607 group of galaxies with the Einstein satellite

We have detected extended X-ray emission around the galaxies NGC 3607, NGC 3605, and NGC 3608 in the group TG 39a = G49 using the IPC aboard the Einstein satellite. We argue that this emission is due to thermal bremsstrahlung from a hot, intergalactic gas; this gas sits in the potential well of the group, around the dominant galaxy NGC 3607. We thus confirm the prediction made earlier that hot, intergalactic gas should be there to keep galaxies clear of gas, since previous sensitive H I observations of this group did not show evidence of neutral hydrogen (Biermann, Clarke, and Fricke). The gas has a density of about 4 x 10/sup -3/ cm/sup -3/, a temperature of about 5 x 10/sup 6/ K, a mass of about 6 x 10/sup 9/ M/sub sun/, and a cooling time of about 5dagger10/sup 9/ yr. The spatial structure of the X-ray emission around NGC 3607 suggests that the dominant galaxy is being stripped at present (cf. Lea and De Young). The X-ray luminosity and velocity dispersion of the galaxies in the group place it on the relation predicted by Silk and Tarter for groups and clusters of galaxies. We discuss the cosmological implications of this detection.