Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004mas..conf..169n&link_type=abstract
MULTIWAVELENGTH AGN SURVEYS. Proceedings of the Guillermo Haro Conference 2003. Held 8-12 December 2003 in Cozumel, Mexico. Edit
Astronomy and Astrophysics
Astronomy
Scientific paper
This article focuses on the radio properties of the ~470 nearby bright (northern) galaxies of the Palomar spectroscopic sample. Almost half the sample's galaxies have nuclei with emission-lines characteristic of AGN but with LHα ≤ 1040 erg s-1. These are referred to as low-luminosity AGNs or LLAGNs. The power source of such LLAGNs has been long debated. High resolution radio surveys of the sample - with the VLA at 15 GHz (150 mas resolution), and the VLBA at 5 GHz (2 mas resolution) - have now revealed a high incidence of pc-scale radio cores with implied brightness temperatures ≳ 108 K, and sub-parsec scale jets. The results support the presence of accreting black holes in ≥50% of all LLAGNs; there is no evidence against all LLAGNs being mini-AGNs. The detected parsec-scale radio cores are almost exclusively found in massive ellipticals and in type 1 (i.e. with broad Hα emission) nuclei. These nuclei follow the usual correlations between radio and emission-line gas properties found in more powerful AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs extends three orders of magnitude below, and is continuous with, that of `classical' AGNs. We find marginal evidence for a low-end turnover in the RLF; nevertheless LLAGNs are responsible for a significant fraction of accretion in the local universe. Low accretion rates (≤ 10-2 - 10-3 of the Eddington rate) are implied in both advection- and jet-type models. Within the context of jet models, the accretion energy output is dominated by the energy in the jet rather than the radiated bolometric luminosity. These jets would be able to dump sufficient energy into the innermost parsecs to significantly slow the accretion inflow. Detailed results can be found in Nagar et al. 2002; 2004 and references therein.
Falcke Heino
Nagar Neil M.
Wilson Andrew S.
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