Water masers in the Local Group of galaxies

We compare the number of detected 22 GHz H2O masers in the Local Group galaxies M31, M33, 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 M33 and NGC 6822 using the Very Large Array (VLA) and incorporated results from previous studies. We observed 62 H regions in M33 and 36 regions with Hα emission in NGC 6822. Detection limits are 0.0015 and 0.0008 L⊙ for M33 and NGC 6822, respectively (corresponding to 47 and 50 mJy in three channels with 0.7 km s−1 width). M33 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 M31, M33, 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.