* Astronomy

Title: GMRT observations of IC 711 - The longest head-tail radio galaxy known
Author: Shweta Srivastava, Ashok K. Singal

We present low-frequency, Giant Metrewave Radio Telescope (GMRT) observations at 240, 610 and 1300 MHz of IC 711, a narrow angle tail (NAT) radio galaxy. The galaxy lies in Abell cluster 1314 (redshift ~ 0.034) and has a long radio tail of total angular extent ~17 arcmin, corresponding to a projected linear size of ~700 kpc. This makes it the longest head-tail radio galaxy known. The objectives of the GMRT observations were to investigate the diffuse-emission of the long tail structure at low frequencies. The radio structure, especially initial ~10 arcmin of tail being a long straight feature, does not seem to be consistent with a simple circular motion around the cluster center, as previously suggested in the literature. Two sharp bends after the straight section of the tail cast doubt on the prevailing idea in the literature that the long narrow tails represent trails left behind by the fast moving parent optical galaxy with respect to the cluster medium, as the optical galaxy could not have undergone such sharp bends in its path, under any conceivable gravitational influence of some individual galaxy or of the overall cluster gravitational potential. In fact the tail does not seem to have been influenced by the gravitational field of any of the cluster-member galaxy. The radio tail shows a break in the spectrum. We derive an expression for the minimum energy in the case of a spectral break, in order to do the minimum energy calculation in diffuse tail regions of IC 711.

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