ROSAT Observations of Five Poor Galaxy Clusters with Extended Radio Sources

Details ROSAT Observations of Five Poor Galaxy Clusters with Extended Radio Sources ROSAT Observations of Five Poor Galaxy Clusters with Extended Radio Sources

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110...46d&link_type=abstract

Astronomical Journal v.110, p.46

Astronomy and Astrophysics

Astronomy

32

Galaxies: Clustering, Galaxies: Individual: Mkw2, Galaxies: Individual: N79-299A, Galaxies: Individual: S49-128, Galaxies: Individual: S49-132, Galaxies: Individual: S49-140

Scientific paper

We present the results of deep ROSAT PSPC observations of the poor clusters MKW2, N79-299A, S49-128, S49-132, and S49-140. These poor clusters all contain extended radio sources, generally with a bent, head- tail (HT) morphology. It had been previously thought that HTs should only be found in rich clusters, which have sufficiently high intracluster medium (ICM) densities and velocity dispersions for effective ram pressure bending of the radio jets. We have found that the X-ray emission associated with these poor clusters is generally quite clumpy and asymmetrical. Often, the clumps are associated with subgroups or individual galaxies, as well as with extended regions around the radio sources. Our results also indicate that there is a continuum of X-ray properties from poor to rich clusters. In many respects, poor clusters seem to be a low-mass extension of rich clusters. We find that these poor clusters have baryon fractions ranging from 1% to 25%. Also, the radio sources within these clusters are probably thermally confined by the ICM. Although four of our clusters have central X-ray luminosity excesses, the implied cooling times are longer than a Hubble time. We interpret the central X-ray luminosity excesses as unresolved galaxy emission. We hypothesize that these poor clusters have recently collapsed out of large, loose clouds of galaxies. We believe that many of the poor cluster properties are understandable in light of this hypothesis. First, four of these five clusters are embedded within larger Zwicky clusters. This may indicate that these large Zwicky clusters act as "incubators" of poor clusters. Second, the observed flat, broad velocity distributions may reflect the velocities associated with the larger-scale systems from which we believe that these poor clusters have collapsed. Third, some of these galaxies (such as NGC 4061, within N79-299A) show signs of interactions with neighboring galaxies with large relative velocities (~850 km/s). Fourth, the observed ICM densities, coupled with velocity distributions which are suggestive of unrelaxed systems, and the peculiar velocities of the radio galaxies may explain the ram pressure bending of the radio jets in the HTs.

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