arXiv subjects

C. H. Ishwara-Chandra

Publications and source records attributed to C. H. Ishwara-Chandra.

93 records · Page 6Linked to original sources

arXiv1999

Evolution of Giant Radio Sources

We present radio images of two giant quasars from the Molonglo/1Jy sample, and make a comparative study of giant radio sources selected from the literature with 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme. The luminosity-size diagram shows that the giant sources are less luminous than smaller-sized sources, consistent with evolutionary scenarios where the giants have evolved from the smaller sources, losing energy as they expand. For the giant sources the equipartition magnetic fields are smaller, and inverse-Compton losses with the microwave background radiation dominates over synchrotron losses, while the reverse is true for the smaller sources. The giant radio sources have core strengths similar to those of smaller sources of similar total luminosity; hence their large sizes are unlikely to be due to stronger nuclear activity. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.

astro-ph↗

arXiv1999

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.

astro-ph↗

arXiv1998

A Polarization Study of Radio Galaxies and Quasars selected from the Molonglo Complete Sample

We present total-intensity and linear-polarization observations made with the Very Large Array at $λ$20 and 6 cm of a representative sample of 42 radio galaxies and quasars selected from the Molonglo Complete Sample. The sources have been chosen to be of large size to probe the depolarizing medium on these scales using our present data and later with observations at lower frequencies with the Giant Metrewave Radio Telescope. The $λ$20 and 6 cm data are of similar resolutions and show that depolarization between these two wavelengths is seen largely in only those lobes which are within about 300 kpc of the parent galaxy. Examination of the depolarization of the lobes with arm-length asymmetry shows that depolarization is observed predominantly for the lobe which is closer to the nucleus. There is also a trend for the lobe closer to the nucleus to be brighter, consistent with the scenario that the nearer lobe is interacting with a denser environment which is responsible for the higher depolarization and greater dissipation of energy. We have also examined the depolarization asymmetry of the lobes on opposite sides of the nucleus for galaxies and quasars. This shows that the depolarization asymmetry for quasars is marginally higher than that for galaxies. The depolarization properties of our sample are possibly determined by an asymmetric environment as well as the effects of orientation.

astro-ph↗