Water maser emission in IC 342

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Corresponding author: A. Tarchi, atarchi@mpifr-bonn.mpg.de

Received: 19 September 2001
Accepted: 4 February 2002

Abstract

The detection of 22 GHz water vapor emission from IC 342 is reported, raising the detection rate among northern galaxies with IRAS point source fluxes  Jy to 16%. The maser, associated with a star forming region ~10–15´´ west of the nucleus, consists of a single 0.5 km s^-1 wide feature and reaches an isotropic luminosity of 10^-2  ( Mpc). If the time variability is intrinsic, the maser size is  cm (0.5 mas) which corresponds to a brightness temperature of 10⁹ K. The linewidth, luminosity, and rapid variability are reminiscent of the 8 km s^-1 super maser in Orion-KL. A velocity shift of 1 km s^-1 within two weeks and subsequent rapid fading is explained in terms of a chance alignment of two dense molecular clouds. Observations at 22 GHz toward Maffei 2 are also reported, yielding a 5σ upper limit of 25 mJy for a channel spacing of 1.05 km s^-1.