Milliarcsec-scale radio structure of a matched sample of Seyfert 1 and Seyfert 2 galaxies

Abstract

Abstract.We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5 GHz (wavelength, λ = 6 cm). The Seyferts of the two types were chosen to be matched in several orientation-independent properties, primarily in order to rigorously test predictions of the unified scheme. We detected all the 15 objects that we observed. In this paper we describe the observations and data reduction procedures, and present the VLBI radio images as well as simultaneous Very Large Array images that we obtained for these 15 Seyferts.

Seyfert Galaxies: Nuclear Radio Structure and Unification

“…Column 1: source name; Column 2: distance to the source assuming a cosmology with H 0 = 75 km s −1 Mpc −1 and q 0 = 0; Column 3: total flux density on arcmin-scale at 1.4 GHz (NVSS: Condon et al 1998); Column 4: total flux density on arcsec scale at 5 GHz; Column 5: core flux density on arcsec scale at 5 GHz; Column 6: core flux density on mas scale at 5 GHz; Column 7: radio power on arcmin-scale at 1.4 GHz (NVSS: Condon et al 1998); Column 8: total radio power on arcsec scale at 5 GHz; Column 9: core radio power on arcsec scale at 5 GHz; Column 10: core radio power on mas scale at 5 GHz; Column 11: logarithm of the projected linear size on mas scale at 5 GHz. (Ulvestad & Wilson 1984a, 1984b); (9) 1997 July, VLBA 8.4 GHz measurement (Mundell et al 2000); (10) (Unger et al 1984); (11) Our (Lal et al 2004) measurements; (12) Ulvestad & Wilson 1989;(13) Pedlar et al 1993;(14) Kukula et al 1995;(15) Ulvestad & Wilson 1984a. 1992a) at 1.7 and 2.3 GHz. They reported that compact radio structures are much more common in Seyfert 2 than in Seyfert 1 galaxies in the far-infrared-selected samples, as well as in the combined mid-infrared and optically selected sample.…”

“…Table 4 gives the measured flux densities and the spectral indices for our Seyfert sample. Mrk 348 and Mrk 231 show radio variability (Lal 2002). Mundell et al (2009) using VLA at 8.4 GHz have shown that five sources from their sample of 12 optically selected, early-type Seyfert galaxies show radio variability.…”

“…In Lal et al (2004), we presented the radio images that were obtained from our observations (project code GL022, date of observations 1998 February 18) and described the properties at these scales in the light of past observations. The data from these observations along with published radio data for the unobserved (well studied) sources, viz., Mrk 348, NGC 4151, Mrk 231, and Mrk 926 at both pc and kpc scales and NGC 5135 at kpc scales are used to discuss the impact on the unified scheme hypothesis.…”

“…A question that can be addressed with the help of the pc-scale and kpc-scale data for our Seyfert sample (Lal et al 2004) is whether the cores of Seyfert galaxies are primarily made up of radio supernovae. To examine whether compact starbursts alone can power Seyfert galaxies, we consider the following arguments.…”

“…In this paper, we first describe the construction of the sample (Section 2) and use the radio maps for 15 objects presented in our earlier paper (Lal et al 2004) along with previously published data for the remaining five objects to interpret our results and their implications on the unification scheme hypothesis (Section 3). In Section 3.7, we also interpret the results of arcsec-scale radio observations of Kukula et al (1995) for the CfA Seyfert galaxy sample (Huchra & Burg 1992) and their implications on the unification scheme hypothesis.…”