Radio and spectroscopic properties of miniature radio galaxies: revealing the bulk of the radio-loud AGN population

• Published in: Astronomy and astrophysics (Berlin) Vol. 508; no. 2; pp. 603 - 614
• Main Authors: Baldi, R. D., Capetti, A.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.12.2009
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; galaxies: active; galaxies: elliptical and lenticular; galaxies: evolution; galaxies: jets; galaxies: nuclei; Galaxy evolution; Elliptical galaxies; Radio galaxies; galaxies: jets; galaxies: evolution; Extended radiosource; Luminosity; Active galaxies; galaxies: elliptical and lenticular, cD; Radio emission; Light emission; galaxies: active; Active galaxy nuclei; Galaxy nuclei; Astronomical catalogues; Cosmic radio sources; Jets; Radio flux; Emission line; Early type galaxies; galaxies: nuclei; Sky surveys
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/200913021

We explore radio and spectroscopic properties of a sample of 14 miniature radio galaxies, i.e. early-type core galaxies hosting radio-loud AGN of extremely low radio power, 1027-29 erg s-1 Hz-1 at 1.4 GHz.
Miniature radio galaxies smoothly extend the relationships found for the more powerful FR I radio galaxies between emission line, optical and radio nuclear luminosities to lower levels. However, they have a deficit of a factor of ~100 in extended radio emission with respect to that of the classical example of 3CR/FR I. This is not due to their low luminosity, since we found radio galaxies of higher radio core power, similar to those of 3CR/FR I, showing the same behavior, i.e. lacking significant extended radio emission. Such sources form the bulk of the population of radio-loud AGN in the Sloan Digital Sky Survey. At a given level of nuclear emission, one can find radio sources with an extremely wide range, a factor of $\ga$100, of radio power.
We argue that the prevalence of sources with luminous extended radio structures in flux limited samples is due to a selection bias, since the inclusion of such objects is highly favored. The most studied catalogues of radio galaxies are thus composed by the minority of radio-loud AGN that meet the physical conditions required to form extended radio sources, while the bulk of the population is virtually unexplored.