Nagar, Wilson, Falcke 2001: Jet Domination in Low-luminosity Active Galactic Nuclei
Evidence for Jet Domination of the Nuclear Radio Emission
in Low-luminosity Active Galactic Nuclei
Neil M. Nagar1, Andrew S. Wilson2,3, Heino Falcke4
1Arcetri Observatory, Largo E. Fermi 5, Florence 50125,
2Astronomy Department, University of Maryland, College Park,
MD 20742-2421 (email@example.com)
3Adjunct Astronomer, Space Telescope Science Institute
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany (firstname.lastname@example.org)
We present simultaneous, sub-arcsecond (<50 pc) resolution
5 GHz, 8.4 GHz, and 15 GHz
observations of a well-defined sample of sixteen low-luminosity active
galactic nuclei (LLAGNs).
The radio emission in most of these nuclei does not show the rising spectrum
(Lnu~nu0.2-1.3) expected from thermal electrons in an
advection dominated accretion flow (ADAF) with or without weak to
Rather, the flat radio spectra are indicative of either
synchrotron self-absorbed emission from jets, convection-dominated
accretion flows (CDAFs) with L>10-5 LEdd,
or ADAFs with strong (p>0.6) outflows.
The jet interpretation is favored by three factors: a) the detection of
pc-scale radio extensions, morphologically reminiscent of jets, in the five
nuclei with the highest peak radio flux-density; b) the domination of
parsec-scale jet radio emission over unresolved `core' emission in the
three best-studied nuclei; and
c) the lack of any clear correlation between radio spectral shape and
black hole mass as would be expected from the dependence of the radio
turnover frequency on black hole mass in ADAF and CDAF models.
A jet domination of nuclear radio emission implies significantly lower
accretion rates in ADAF-type models than earlier estimated from core
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