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Date and Time of the Query: 2019-04-18 T04:08:00 PDT
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For refcode 2013A&A...554A..85S:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2013A&A...554A..85S Low-frequency radio observations of Seyfert galaxies: A test of the unification scheme Singh, V.; Shastri, P.; Ishwara-Chandra, C. H.; Athreya, R. Abstract. Aims: We present low-frequency radio imaging and spectral properties of a well-defined sample of Seyfert galaxies using GMRT 240/610 MHz dual frequency observations. Radio spectra of Seyfert galaxies over 240 MHz to 5.0 GHz are investigated using 240 MHz, 610 MHz flux densities derived from GMRT, and 1.4 GHz and 5.0 GHz 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. Methods: 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. Results: The new observations at 240/610 MHz, together with archival observations at 1.4 GHz, 5.0 GHz show that types 1s and 2s have statistically similar radio luminosity distributions at 240 MHz, 610 MHz, 1.4 GHz, and 5.0 GHz. The spectral indices at selected frequency intervals ({alpha}_240 MHz_^610 MHz^, {alpha}_610 MHz_^1.4 GHz^, and {alpha}_1.4 GHz_^5.0 GHz^), as well as index measured over 240 MHz to 5.0 GHz ({alpha}_int_) for the two Seyfert subtypes, have similar distributions with median spectral index ({alpha}) ~ -0.7 (S_nu_ is proportional to nu^{alpha}^), 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 610 MHz. 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. Figures 2, 4 and Appendix A are available in electronic form at http://www.aanda.org Key words: galaxies: Seyfert, galaxies: active, radio continuum: galaxies
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