An HI study of three long-tailed irregular galaxies in the cluster Abell1367

We present the results on the distribution and kinematics of H\sc{i} gas with higher sensitivity and in one case of higher spectral resolution as well than reported earlier, of three irregular galaxies CGCG 097073, 097079 and 097087 (UGC 06697) in the cluster Abell 1367. These galaxies are known to exhibit long (50$-$75 kpc) tails of radio continuum and optical emission lines (H$\alpha$) pointing away from the cluster centre and arcs of starformation on the opposite sides of the tails. These features as well as the H{\sc i} properties, with two of the galaxies (CGCG 097073 and 097079) exhibiting sharper gradients in H{\sc i} intensity on the side of the tails, are consistent with the H{\sc i} gas being affected by the ram pressure of the intracluster medium. However the H{\sc i} emission in all the three galaxies extends to much smaller distances than the radio-continuum and H$\alpha$ tails, and are possibly still bound to the parent galaxies. Approximately 20$-$30 per cent of the H{\sc i} mass is seen to accumulate on the downstream side due to the effects of ram pressure.Comment: 19 pages, 19 figures, 3 tables, accepted for publication in the Bulletin of the Astronomical Society of Indi

HI gas in rejuvenated radio galaxies: GMRT observations of the DDRG J1247+6723

We report the detection of HI absorption towards the inner double of the double-double radio galaxy (DDRG) J1247+6723 with the Giant Metrewave Radio Telescope (GMRT). The inner double is a Giga-hertz peaked spectrum (GPS) source with a linear size of 14 pc while the overall size defined by the outer double is 1195 kpc, making it a giant radio source. The absorption profile is well resolved and consists of a number of components on either side of the optical systemic velocity. The neutral hydrogen column density is estimated to be N(HI)=6.73*10^{20}(T_s/100)(f_c/1.0) cm^{-2}, where T_s and f_c are the spin temperature and covering factor of the background source respectively. We explore any correlation between the occurrence of HI absorption and rejuvenation of radio activity and suggest that there could be a strong relationship between them.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter

Giant Radio Sources

We present multi-frequency VLA observations of two giant quasars, 0437-244 and 1025-229, from the Molonglo Complete Sample. These sources have well-defined FRII radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure ($\mid RM \mid < 20 rad/m^2$). The giant sources are defined to be those whose overall projected size is $\geq$ 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to the smaller sources of similar total luminosity. Hence their large sizes are unlikely to be due to stronger nuclear activity. The degree of collinearity of the giant sources is also similar to the sample of smaller sources. The luminosity-size diagram shows that the giant sources are less luminous than our sample of smaller-sized 3CR sources, consistent with evolutionary scenarios where the giants have evolved from the smaller sources losing energy as they expand to these large dimensions. For the smaller sources, radiative losses due to synchrotron radiation is more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton losses with the microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.Comment: 14 pages with 12 figures, MNRAS LaTex. Accepted for publication in MNRAS. Minor changes in the text and couple of references adde