Giant and Double-Double Radio Galaxies: Implications for the Evolution of Powerful Radio Sources and the IGM
Giant radio sources form the linear size extreme of the extragalactic radio source population. Using the WENSS survey, we have selected a complete sample of these sources. We have investigated the properties of their radio structures. We find, among other things, that these sources are old (50-100 Myr) and have higher advance velocities than smaller sources of similar radio power. We find pressure gradients in their radio lobes, suggesting that the lobes are still overpressured with respect to the environment. Further, we find no evidence for a cosmological evolution of the radio lobe pressures with increasing redshift, at least up to z~0.4, other than that caused by selection effects. We argue that a much fainter sample of giant sources than currently available is needed to constrain the pressure in their environments, the IGM, and that SKA can play an important role in studying such sources. Another extremely important discovery is that of a population of radio sources with a so-called `double-double' structure, i.e. that of a small two-sided radio source embedded inside a much larger two-sided structure. We argue that these sources result from an interrupted central jet-forming activity. As such, they are the most convincing examples of radio sources with a history of interrupted activity, yet. Since the inner lobes advance within the outer lobes, high resolution low frequency (100 - 1000 MHz) polarization studies may reveal the constituents of radio lobes and cocoons. We thus argue for a SKA design that can provide low-frequency polarization images at arcsec resolution, but which is also sensitive to structures as large as a few tens of arcminute on the sky.
Perspectives on Radio Astronomy: Science with Large Antenna Arrays
- Pub Date:
- 8 pages, 4 figures, uses nfraconf.sty. To appear in the proceedings of NFRA conference "Perspectives of radio astronomy: Scientific Imperatives at cm and m Wavelengths", Amsterdam, 7-9 April 1999, Ed. M.P. van Haarlem, J.M. van der Hulst