Hubble Space Telescope and very large array observations of the H2O gigamaser galaxy TXS 2226-184

We present Hubble Space Telescope/Wide-Field and Planetary Camera 2 images in H alpha + [N II] lambda lambda 6548, 6583 lines and continuum radiation and a VLA map at 8 GHz of the H2O gigamaser galaxy TXS 2226-184. 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 degrees). The color map confirms that the dust lane is aligned with the galaxy major axis and is crossing the putative nucleus. The H alpha + [N II] map exhibits a gaseous, jetlike structure perpendicular to the nuclear dust lane and the galaxy major axis. The radio map shows compact, steep spectrum emission that is elongated in the same direction as the H alpha + [N II] emission. By analogy with Seyfert galaxies, we therefore suspect that this alignment reflects an interaction between the radio jet and the interstellar medium. The axes of the nuclear dust disk, the radio emission, and the optical line emission apparently define the axis of the active galactic nucleus. 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.