Host galaxies and nuclear structure of AGN with H_2O megamasers as seen with HST

Abstract

We present results of an HST survey in Halpha and continuum filters of a sample of H_2O megamaser galaxies compiled by Braatz et al., all of which contain AGN. These observations allow us to study the AGN/host-galaxy connection, e.g. study the relation between the parsec scale masing disk/torus, bipolar outflows, and large scale properties of the galaxies such as dust lanes, signs for interaction, and galaxy types. A number of galaxies indeed show large-scale bi-polar Halpha structures which, however, are more reminiscent of outflows then excitation cones. Most megamaser galaxies are found in spiral galaxies. Only one galaxy in the original sample is known to be an elliptical and one galaxy imaged by us shows clear signs of interactions. In all cases we see evidence for obscuration of the nucleus (e.g. dust-lanes) in our color maps and the disk galaxies are preferentially edge on. This suggests that the nuclear masing disk has some relation to the large scale properties of the galaxy and the dust distribution.

6 pages, 4 figures, Kluwer Latex, to appear in: ``QSO hosts and Their Environments'', Granada, January 2001, Eds. I. Marquez Perez et al., Kluwer Academic Press, also available at http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#h2ohosts