Astronomy and Astrophysics, volume 554A, 85-85 (2013/6-1)
Low-frequency radio observations of Seyfert galaxies: a test of the unification scheme.
SINGH V., SHASTRI P., ISHWARA-CHANDRA C.H. and ATHREYA R.
Abstract (from CDS):
We present low-frequency radio imaging and spectral properties of a well-defined sample of Seyfert galaxies using GMRT 240/610MHz dual frequency observations. Radio spectra of Seyfert galaxies over 240MHz to 5.0GHz are investigated using 240MHz, 610MHz flux densities derived from GMRT, and 1.4GHz and 5.0GHz flux densities mainly from published VLA data. We test the predictions of Seyfert unification scheme by comparing the radio properties of Seyfert type 1s and type 2s. We chose a sample such that the two Seyferts subtypes have matched distributions in parameters that are independent of the orientation of AGN, obscuring torus, and the host galaxy. Our sample selection criteria allowed us to assume that the two Seyfert subtypes are intrinsically similar within the framework of the unification scheme. The new observations at 240/610MHz, together with archival observations at 1.4GHz, 5.0GHz show that types 1s and 2s have statistically similar radio luminosity distributions at 240MHz, 610MHz, 1.4GHz, and 5.0GHz. The spectral indices at selected frequency intervals (α240MHz610MHz, α610MHz1.4GHz, and α1.4GHz5.0GHz), as well as index measured over 240MHz to 5.0GHz (αint) for the two Seyfert subtypes, have similar distributions with median spectral index (α)~-0.7(Sν∝να), consistent with the synchrotron emission from optically thin plasma. In our snapshot 240/610 MHz GMRT observations, most of the Seyfert galaxies primarily show an unresolved central radio component, except for a few sources in which faint kpc-scale extended emission is apparent at 610MHz. Our results on the statistical comparison of the multifrequency radio properties of our sample Seyfert galaxies agree with the predictions of the Seyfert unification scheme.
galaxies: Seyfert - galaxies: active - radio continuum: galaxies