A radio census of nuclear activity in nearby galaxies

¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150 – 762 Porto, Portugal e-mail: mfilho@astro.up.pt
² Istituto di Radioastronomia, CNR, via P. Gobetti, 101, 40129 Bologna, Italy
³ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
⁴ The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA

Received: 10 November 2005
Accepted: 30 December 2005

Abstract

In order to determine the incidence of black hole accretion-driven nuclear activity in nearby galaxies, as manifested by their radio emission, we have carried out a high-resolution Multi-Element Radio-Linked Interferometer Network (MERLIN) survey of LINERs and composite LINER/Hii galaxies from a complete magnitude-limited sample of bright nearby galaxies (Palomar sample) with unknown arcsecond-scale radio properties. There are fifteen radio detections, of which three are new subarcsecond-scale radio core detections, all being candidate AGN. The detected galaxies supplement the already known low-luminosity AGN – low-luminosity Seyferts, LINERs and composite LINER/Hii galaxies – in the Palomar sample. Combining all radio-detected Seyferts, LINERs and composite LINER/Hii galaxies (LTS sources), we obtain an overall radio detection rate of 54% (22% of all bright nearby galaxies) and we estimate that at least ~50% (~20% of all bright nearby galaxies) are true AGN. The radio powers of the LTS galaxies allow the construction of a local radio luminosity function. By comparing the luminosity function with those of selected moderate-redshift AGN, selected from the 2dF/NVSS survey, we find that LTS sources naturally extend the RLF of powerful AGN down to powers of about 10 times that of Sgr A*.