Letter to the Editor

Large-scale HI in nearby radio galaxies: segregation in neutral gas content with radio source size

¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
² Department of Astronomy, Columbia University, Mail Code 5246, 550 West 120th Street, New York, NY 10027, USA e-mail: emonts@astro.columbia.edu
³ Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ National Radio Astronomy Observatory, Socorro, NM 87801, USA
⁵ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK

Received: 1 August 2006
Accepted: 22 December 2006

Abstract

We present results of a study of neutral hydrogen (H I) in a complete sample of nearby non-cluster radio galaxies. We find that radio galaxies with large amounts of extended H I () all have a compact radio source. The host galaxies of the more extended radio sources, all of Fanaroff & Riley type-I, do not contain these amounts of H I. We discuss several possible explanations for this segregation. The large-scale H I is mainly distributed in disk- and ring-like structures with sizes up to 190 kpc and masses up to . The formation of these structures could be related to past merger events, although in some cases it may also be consistent with a cold-accretion scenario.