The accretion mechanism in low power radio-galaxies.

Details The accretion mechanism in low power radio-galaxies. The accretion mechanism in low power radio-galaxies.

Oct 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agn8.confe...8b&link_type=abstract

Proceedings of the 8th National Conference on AGN, held in Torino, Italy, May 19-22, 2008. Edited by L. Lanteri, C.M. Raiteri,

Computer Science

Scientific paper

We considered a sample of 44 low luminosity radio-loud AGN, covering a range of nuclear radio-power of 5 orders of magnitude, in order to unveil the mechanism of accretion at work in these galaxies. We estimated the accretion rate of gas associated to their hot coronae by analyzing archival Chandra, deriving the de-projected density and temperature profiles, in a spherical approximation. Having determined the jet power from the nuclear radio-luminosity, we found that the accretion power correlates linearly with the jet power, with an efficiency of conversion from rest mass into jet power of ~ 0.016. These results strengthen and extend the validity of the results obtained by Allen et al. (2006) from a sample of 9 galaxies, indicating that hot gas accretion is the dominant process in FR I radio-galaxies across their full range of radio-luminosity. In addition, we found that the different levels of nuclear activity are driven by global differences in the structure of the galactic hot coronae. In fact, a linear relation links the jet power with the host X-ray surface brightness. This implies that a substantial change in the jet power must be accompanied by a global change in its ISM properties, driven e.g. by a major merger. This correlation also provides us with a simple and widely applicable method to estimate the jet-power of a given object, with an uncertainty of a factor of ~ 5, by just looking at the intensity of the host X-ray emission. In order to maintain the mass flow in the jet, the fraction of gas crossing the Bondi radius that actually reaches the accretion disk must be > ~ 0.01 . This implies that the radiative efficiency of the disk must be < ~ 0.005 , an indication that accretion in these objects occurs not only at a smaller rate, but also at lower efficiency than in standard accretion disks.

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