Large-scale gas disk around the radio galaxy Coma A^*

¹ Netherlands Foundation for Research in Astronomy, PO Box 2, 7990 AA, Dwingeloo, The Netherlands
² Istituto di Radioastronomia, CNR, via Gobetti 101, 40129 Bologna, Italy
³ Dep. Physics and Astronomy, University of Sheffield, Sheffield, S7 3RH, UK
⁴ National Radio Astronomy Observatory, Socorro, NM 87801, USA

Corresponding author: R. Morganti, morganti@nfra.nl

Received: 19 December 2002
Accepted: 1 March 2002

Abstract

We present WSRT and VLA radio observations of the neutral hydrogen in the radio galaxy Coma A. We detect extended absorption against both radio lobes of Coma A, at distances of about 30 kpc from the centre. Coma A is the first radio galaxy in which is seen in absorption at such large distances from the nucleus. The match between the velocities of the neutral hydrogen and those of the extended ionized gas suggests that they are part of the same disk-like structure of at least 60 kpc in diameter. Most likely, this gas disk is partly ionised by the bulk motion of the radio lobes expanding into it. The gas mass of this disk is at least 10⁹ . The relatively regular structure of the gas disk suggests that a merger occurred involving at least one large gas-rich galaxy, at least a few times 10⁸ yr ago.