Radio properties of low-redshift broad-line active galactic nuclei including extended radio sources.
RAFTER S.E., CRENSHAW D.M. and WIITA P.J.
Abstract (from CDS):
We present a study of the extended radio emission in a sample of 8434 low-redshift (z < 0.35) broad-line active galactic nuclei (AGNs) from the Sloan Digital Sky Survey. To calculate the jet and lobe contributions to the total radio luminosity, we have taken the 846 radio core sources detected in our previous study of this sample and performed a systematic search in the FIRST database for extended radio emission that is likely associated with the optical counterparts. We found that 51 out of 846 radio core sources have extended emission (>4'' from the optical AGN) that is positively associated with the AGN, and we have identified an additional 12 AGNs with extended radio emission but no detectable radio core emission. Among these 63 AGNs, we found 6 giant radio galaxies, with projected emission exceeding 750 kpc in length, and several other AGNs with unusual radio morphologies also seen in higher redshift surveys. The optical spectra of many of the extended sources are similar to those of typical broad-line radio galaxy spectra, having broad Hα emission lines with boxy profiles and large MBH. With extended emission taken into account, we find strong evidence for a bimodal distribution in the radio-loudness parameter (≡νradioLradio/νopt Lopt), where the lower radio luminosity core-only sources appear as a population separate from the extended sources, with a dividing line at log() ~1.75. This dividing line ensures that these are indeed the most radio-loud AGNs, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio-quiet AGNs.
galaxies: active - galaxies: nuclei - galaxies: Seyfert - radio continuum: galaxies