2008ApJ...686L..13G

Of 104 AGNs known to exhibit H₂ O maser emission, X-ray data that enable estimation of column densities, or lower limits, are available for 42. Contributing to this, we report analysis of new and archival X-ray data for eight galaxies and collation of values for three more. Maser emission is indicative of large columns of cold gas, and in five of the eight new cases, maser spectra point toward origins in accretion disks viewed close to edge-on (a.k.a. ``disk maser'' systems). In these, we detect hard continuum and Fe Kα emission with equivalent widths on the order of 1 keV, which is consistent with Compton reflection, fluorescence by cold material, and obscuring columns ≳10²⁴/cm2. Reviewing the full sample of 42, 95% exhibit N_H>10²³/cm2 and 60% exhibit N_H>10²⁴/cm2. Half of these are now recognized to be disk masers (up from 13); in this subsample, which is likely to be more homogeneous vis-á-vis the origin of maser emission, 76% exhibit N_H>10²⁴/cm2. The probability of a common parent distribution of columns for disk masers and other AGN masers is ≲3%. Because ground-based surveys of AGNs to detect new disk masers are relatively unbiased with respect to X-ray brightness and comparatively inexpensive, they may also be efficient guides for the sensitive pointed X-ray observations required to identify Compton-thick objects outside of shallow surveys.