HST and VLA Observations of the H2O Gigamaser Galaxy TXS2226-184

Abstract

We present HST/WFPC2 images in Halpha+[NII]6548,6583 lines and continuum radiation and a VLA map at 8 GHz of the H2O gigamaser galaxy TXS2226-184. This galaxy has the most luminous H2O maser emission known to date. Our red continuum images reveal a highly elongated galaxy with a dust lane crossing the nucleus. The surface brightness profile is best fitted by a bulge plus exponential disk model, favoring classification as a highly inclined spiral galaxy (i=70 degree). The color map confirms the dust lane aligned with the galaxy major axis and crossing the putative nucleus. The Halpha+[NII] map exhibits a gaseous, jet-like structure perpendicular to the nuclear dust lane and the galaxy major axis. The radio map shows compact, steep spectrum emission which is elongated in the same direction as the Halpha+[NII] emission. By analogy with Seyfert galaxies, we therefore suspect this alignment reflects an interaction between the radio jet and the ISM. The axes of the nuclear dust disk, the radio emission, and the optical line emission apparently define the axis of the AGN. The observations suggest that in this galaxy the nuclear accretion disk, obscuring torus, and large scale molecular gas layer are roughly coplanar. Our classification of the host galaxy strengthens the trend for megamasers to be found preferentially in highly inclined spiral galaxies.