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Astron. Astrophys. 362, 27-41 (2000)

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

S. Jeyakumar 1, D.J. Saikia 1, A. Pramesh Rao 1 and V. Balasubramanian 2

1 National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Post Bag No. 3, Ganeshkhind, Pune 411 007, India
2 Radio Astronomy Centre, Tata Institute of Fundamental Research, Post Box No. 8, Udhagamandalam 643 001, India

Received 5 October 1999 / Accepted 11 August 2000

Abstract

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 Scintillation (IPS) with the Ooty Radio Telescope. Our observations provide structural information on angular scales ranging from about 50 to a few hundred milliarcsec. We estimate the size and flux density of the scintillating components from the IPS observations. The fraction of flux density of the hotspots estimated from both the IPS observations as well as from interferometric observations for larger sources from the literature exhibits no significant dependence on either the radio luminosity or linear size for the high-luminosity sources. We examine the collimation of radio jets using the sizes of hotspots from both IPS and interferometric observations. The hotspot sizes 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 IPS observations show evidence of larger-scale structures compared to the known VLBI-scale structures in 8 CSS and GPS radio sources. We discuss the origin of these structures. We also examine the spectra of compact components in GPS sources using both IPS and interferometric measurements, and attempt to distinguish between different processes for explaining their low-frequency spectra.

Key words: galaxies: active – galaxies: jets – galaxies: quasars: general – radio continuum: galaxies

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100
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