Small-scale structures in compact steep-spectrum and GHz-peaked-spectrum radio sources

We determine the small-scale structure for a large sample of Compact Steep Spectrum (CSS) and Gigahertz Peaked Spectrum (GPS) sources and a sample of larger radio sources at 327 MHz using the technique of Inter-Planetary Scin tillation (IPS) with the Ooty Radio Telescope. Our observations provide str uctural information on angular scales ranging from about 50 to a few hundre d millarcsec. We estimate the size and Aux density of the scintillating com ponents from the IFS observations. The fraction of flux density of the hots pots estimated from both the IFS observations as well as from interferometr ic observations for larger sources from the literature exhibits no signific ant dependence on either the radio luminosity or linear size for the high-l uminosity sources. We examine the collimation of radio jets using the sizes of hotspots from both TPS and interferometric observations. The hotspot si zes do not exhibit a significant dependence on the overall linear size for the larger sources, although the CSS and GPS sources were earlier found to evolve in a self-similar way. The IFS observations show evidence of larger- scale structures compared to the known VLBI-scale structures in 8 CSS and G PS radio sources. We discuss the origin of these structures. We also examin e the spectra of compact components in GPS sources using both IFS and inter ferometric measurements, and attempt to distinguish between different proce sses for explaining their low-frequency spectra.