Head tail sources in poor clusters of galaxies

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Session 98 -- Galaxies and Cluster Environment
Oral presentation, Friday, January 14, 2:15-3:45, Salon V Room (Crystal Gateway)

[98.03] Head tail sources in poor clusters of galaxies

T.C.A.Venkatesan, D.J.Batuski (Univ. of Maine), R.J.Hanisch (STScI), J.O.Burns (NMSU)

Head tail sources in poor clusters of galaxies have been studied using the VLA at wavelengths of 6 cm and 20 cm. Four sources (NGC 742, NGC 1044, NGC 4061 and NGC 7503) were selected from a larger sample for detailed study. These sources represent an exceptional opportunity to study radio jets and their interaction with the cluster environment, in detail, because of their proximity ($z \sim$ 0.02 to 0.04). NGC 4061 and NGC 7503 exhibit narrow-angle-tail (NAT) morphologies similar to the classic rich cluster NAT, NGC 1265. NGC 742 has a complex morphology while NGC 1044 shows a wide-angle-tail (WAT) morphology.

The NAT morphologies are believed to be the result of the intracluster medium (ICM) ram pressures. The poor cluster NATs are thus remarkable because the poor cluster ICM ram pressure is expected to be much lower, in general, than in rich clusters. Comparisons of the results of the poor cluster sources with those of NGC 1265 should reveal much about the radio source and cluster environment interaction. Most of the parameters calculated such as jet luminosity as a fraction of total source luminosity, jet opening angle, jet radius of curvature and the ICM density surrounding the sources are quite similar between NGC 1265 and the poor cluster sources. This is a very surprising result and we conclude that ICM densities typical of poor clusters and a galaxy relative velocity $\approx$ 1000 km s$^{-1}$ provide sufficient ram pressure to bend radio jets into NAT morphologies.

Spectral indices and polarization structures have been compared between the rich and poor clusters and are found to be similar as well. The spectral indices in the poor cluster sources ($\alpha_{jet}$ $\approx$ -0.6 and $\alpha_{tail} $\approx$ -0.8) are similar to those of the rich cluster sources. The fractional polarizations vary from $\sim$ 10$\%$ in the jets to $\sim$ 30$\%$ in the tails similar to the rich cluster HT sources. The magnetic field structure appears to follow the general structure seen in low luminosity radio sources. The overall result is the remarkable similarity between the HT phenomenon in the rich and poor clusters.

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