Water masers in the Local Group of galaxies

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: brunthal@mpifr-bonn.mpg.de
² Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611, Australia
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵ ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁶ Department of Astrophysics, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL Nijmegen, The Netherlands

Received: 22 May 2006
Accepted: 22 June 2006

Abstract

We compare the number of detected 22 GHz H₂O masers in the Local Group galaxies M 31, M 33, NGC 6822, IC 10, IC 1613, DDO 187, GR8, NGC 185, and the Magellanic Clouds with the water maser population of the Milky Way. To accomplish this we searched for water maser emission in the two Local Group galaxies M 33 and NGC 6822 using the Very Large Array (VLA) and incorporated results from previous studies. We observed 62 Hii regions in M 33 and 36 regions with Hα emission in NGC 6822. Detection limits are 0.0015 and 0.0008  for M 33 and NGC 6822, respectively (corresponding to 47 and 50 mJy in three channels with 0.7 km s^-1 width). M 33 hosts three water masers above our detection limit, while in NGC 6822 no maser source was detected. We find that the water maser detection rates in the Local Group galaxies M 31, M 33, NGC 6822, IC 1613, DDO 187, GR8, NGC 185, and the Magellanic Clouds are consistent with expectations from the Galactic water masers if one considers the different star formation rates of the galaxies. However, the galaxy IC 10 exhibits an overabundance of masers, which may result from a compact central starburst.