Nagar, Falcke et al.: Radio Sources in Low-Luminosity Active Galactic Nuclei. III. ``AGNs'' in a Distance-Limited Sample of ``LLAGNs''
Radio Sources in Low-Luminosity Active Galactic Nuclei.
III. ``AGNs'' in a Distance-Limited Sample of ``LLAGNs''
Neil M. Nagar1, Heino Falcke2, Andrew S. Wilson1,3, James S. Ulvestad4
1Arcetri Observatory, Largo E. Fermi 5,Florence 50125, Italy (firstname.lastname@example.org)
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany (email@example.com)
3Astronomy Department, University of Maryland, College Park,
MD 20742-2421 (firstname.lastname@example.org)
Adjunct Astronomer, Space Telescope Science Institute
4National Radio Astronomy Observatory, P.O. Box 0,
Socorro, NM 87801, U.S.A. (email@example.com)
This paper presents the results of a high resolution radio imaging survey
of all known (96) low-luminosity active galactic nuclei (LLAGNs) at d<19Mpc.
We first report new 2 cm (150 mas resolution using the VLA) and 6 cm
(2 mas resolution using the VLBA)
radio observations of the previously unobserved nuclei in our samples and
then present results on the complete survey.
We find that almost half of all LINERs and low-luminosity Seyferts have
flat-spectrum radio cores when observed at 150 mas resolution.
Higher (2 mas) resolution observations of a flux-limited subsample have
provided a 100% (16 of 16) detection rate of pc-scale radio cores, with
implied brightness temperatures >10^8 K. The five LLAGNs with the
highest core radio fluxes also have pc-scale `jets.'
Compact radio cores are almost exclusively found in massive ellipticals
and in type 1 nuclei (i.e. nuclei with broad Halpha emission).
Only a few `transition' nuclei have compact radio cores; those detected
in the radio have optical emission-line diagnostic ratios close to those of
LINERs/Seyferts. This indicates that some transition nuclei are truly
composite Seyfert/LINER+HII region nuclei, with the radio core power
depending on the strength of the former component.
The core radio power is correlated with the nuclear optical emission-line
luminosity and width, and with the galaxy luminosity.
In these correlations LLAGNs fall close to the low-luminosity
extrapolations of more powerful AGNs.
The scalings suggest that many of the radio-non-detected LLAGNs are simply
lower power versions of the radio-detected LLAGNs.
The ratio of core radio power to nuclear optical emission-line luminosity
increases with increasing bulge luminosity for all LLAGNs. Also, there is evidence
that the luminosity of the disk component of the galaxy is correlated with the
nuclear emission-line luminosity (but not the core radio power).
About half of all LLAGNs with multiple epoch data show significant inter-year
Investigation of a sample of ~150 nearby bright galaxies, most of them
LLAGNs, shows that the nuclear (<150 mas size) radio power is strongly
correlated with both the black hole mass and the galaxy bulge luminosity.
Low accretion rates (<10^-2 - 10^-3 of the Eddington rate) are implied
in both ADAF- and jet-type models.
In brief, all evidence points towards the presence of accreting massive black
holes in a large fraction, perhaps all, of LLAGNs, with the nuclear radio
emission originating in either the accretion inflow onto the massive black hole
or from jets launched by this black hole - accretion disk system.
Paper: Available in full length as PostScript
and LaTex (AAS LaTex) Format.
Other publications can be found here.
Questions: Heino Falcke, firstname.lastname@example.org