ROSAT OBSERVATIONS OF THE B2 RADIO GALAXIES-1615-1621+38 - IMPLICATIONS FOR THE RADIO-SOURCE CONFINEMENT(35 AND GALAXIES)

We report X-ray observations of the radio galaxies B2 1615+35 (NGC 610 9) and B2 1621+38 (NGC 6137), which belong to poor groups of galaxies and are characterized by a ''head-tail'' structure. We also analyze th e X-ray behaviour of the radio galaxy NGC 6107, present within the fie ld of view and showing a symmetric extended radio structure. The X-ray emission from the group of 1615+35 is complex, including both emissio n from a hot intergroup gas, and emission from the individual radio ga laxies (1615+35 itself, which is pointlike, and NGC 6107, which is ext ended). In the case of 16211+38, only extended X-ray emission from the galaxy itself is detected. The extended X-ray emission of the galaxie s 1621+38 and NGC 6107 is probably related to a gaseous galactic atmos phere. The pointlike emission of the radio galaxy 1615+35, instead, is likely to originate in the nucleus. We discuss the confinement of rad io components by the ambient gas, and find that the external thermal p ressure exceeds the internal equipartition pressure. The X-ray emittin g plasma in the 1615+35 group is characterized by luminosity, temperat ure and metallitcity typical for groups, i.e. lower than for rich clus ters. Its total mass is similar to 1/20 of the mass derived assuming h ydrostatic equilibrium, implying that this group is likely to be domin ated by dark matter, in agreement with results on other groups. A simi lar behaviour is found for the two coronas of NGC 6107 and 1621+38.