Site Map
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

The host galaxies of radio-loud active galactic nuclei: mass dependences, gas cooling and active galactic nuclei feedback

P. Best, G. Kauffmann, T. Heckman, J. Brinchmann, S. Charlot, Z. Ivezic, S. D. M. White

The properties of the host galaxies of a well-defined sample of 2215 radio-loud active galactic nuclei (AGN) with redshifts 0.03 〈 z 〈 0.3, defined from the Sloan Digital Sky Survey (SDSS), are investigated. These are predominantly low radio-luminosity sources, with 1.4-GHz luminosities in the range 1023-1025 WHz-1. The fraction of galaxies that host radio-loud AGN with L1.4GHz 〉 1023WHz-1 is a strong function of stellar mass, rising from nearly zero below a stellar mass of 1010Msolar to more than 30 per cent at stellar masses of 5 × 1011Msolar. In contrast to the integrated [OIII] luminosity density from emission-line AGN, which is mainly produced by black holes with masses below 108Msolar, the integrated radio luminosity density comes from the most massive black holes in the Universe. The integral radio luminosity function is derived in six ranges of stellar and black hole masses. Its shape is very similar in all of these ranges and can be well fitted by a broken power law. Its normalization varies strongly with mass, as M2.5* or M1.6BH; this scaling only begins to break down when the predicted radio-loud fraction exceeds 20-30 per cent. There is no correlation between radio and emission-line luminosities for the radio-loud AGN in the sample and the probability that a galaxy of given mass is radio loud is independent of whether it is optically classified as an AGN. The host galaxies of the radio-loud AGN have properties similar to those of ordinary galaxies of the same mass, with a tendency for radio-loud AGN to be found in larger galaxies and in richer environments. The host galaxies of radio-loud AGN with emission lines match those of their radio-quiet counterparts.

All of these findings support the conclusion that the optical AGN and low radio-luminosity AGN phenomena are independent and are triggered by different physical mechanisms. Intriguingly, the dependence on black hole mass of the radio-loud AGN fraction mirrors that of the rate at which gas cools from the hot atmospheres of elliptical galaxies. It is speculated that gas cooling provides a natural explanation for the origin of the radio-loud AGN activity, and it is argued that AGN heating could plausibly balance the cooling of the gas over time.

Monthly Notices of the Royal Astronomical Society
Volume 362, Page 25
September 2005

>> PDF>> ADS

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website