Circumnuclear Structures in Megamaser Host Galaxies

Abstract

Using HST, we identify circumnuclear ($100$-$500$ pc scale) structures in nine new H${}_2$O megamaser host galaxies to understand the flow of matter from kpc-scale galactic structures down to the supermassive black holes (SMBHs) at galactic centers. We double the sample analyzed in a similar way by Greene et al. (2013) and consider the properties of the combined sample of 18 sources. We find that disk-like structure is virtually ubiquitous when we can resolve $<200$ pc scales, in support of the notion that non-axisymmetries on these scales are a necessary condition for SMBH fueling. We perform an analysis of the orientation of our identified nuclear regions and compare it with the orientation of megamaser disks and the kpc-scale disks of the hosts. We find marginal evidence that the disk-like nuclear structures show increasing misalignment from the kpc-scale host galaxy disk as the scale of the structure decreases. In turn, we find that the orientation of both the $\sim 100$ pc scale nuclear structures and their host galaxy large-scale disks is consistent with random with respect to the orientation of their respective megamaser disks.

24 pages, 16 figures, 4 tables; Resubmitted to ApJ after referee's comments

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