Location of H2O maser in the double-nuclei system of NGC 6240

Abstract

We performed VLA observations of the 22 GHz H2O maser emission in the merging galaxy NGC 6240, which hosts the well-known double active nuclei. In a previous paper, we reported on the first solid detection of the H2O maser emission in 2001. After two abortive attempts due to the weakness and probable variability of the emission, the maser was detected with the VLA in June 2002. The emission is unresolved at ∼0.3 arcsec and coincides with the southern 22 GHz continuum peak to ∼0.007 arcsec (∼3 pc: D = 97 Mpc). The detection of the maser in the southern nucleus indicates that nuclear activity of the galaxy, which is significant in X-ray and far-infrared (FIR) bands, lies mainly in the southern nucleus, and the nucleus without a high brightness peak could be explained by thick dust emitting FIR radiation. We favour the idea that the maser in NGC 6240 is associated with the AGN-activity.