deletions | additions       diff --git a/h2o_megamasers.tex b/h2o_megamasers.tex  index 9b50f49..8dee95a 100644  --- a/h2o_megamasers.tex  +++ b/h2o_megamasers.tex 
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Numerous surveys have been undertaken to find H$_2$O mega-maser detections, notably by \citet{Braatz_1996}, who surveyed {\it all} nearby galaxies with AGN characteristics (see also \citet{Braatz_1997}). The Megamaser Cosmology Project is an on-going H$_2$O mega-maser survey of known sources that combines high- and low-resolution observations over long time periods to obtain geometric distances to galaxies beyond $\gt 100$ Mpc, and infer H$_0$ to a high precision, independent of other methods (\S\ref{sub:h2o_cosmo}) \citep{reid2009_mmproject_I}. Given the applications discussed in the preceding sections, many more H$_2$O mega-maser will be conducted as more sensitive instrumentation becomes available.  \subsection{Extragalactic Properties}  \label{sub:h2o_props} \subsection{Host galaxies}  \label{sub:h2o_hosts}  The detection rate for nearby Sy2 and LINER galaxies is about $1/4$, while the overall detection rate for all AGN observed is just $5\%$ \citep{tarchi2012}. What is the cause of this significant difference between different classes of AGN? 
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Seyfret 1 galaxies are predicted to be observed face-on; one H$_2$O mega-maser has been observed from this class in NGC 2782 and it remains unclear on how this arises \citep{Tarchi_2011}. However, \citet{Tarchi_2011} also find a high occurence rate (corrected for the volume-limited sample) for H$_2$O mega-masers in narrow-line Sy1 galaxies, a subset of Sy1 galaxies that exhibit narrow Balmer lines and strong Fe II emission \citep{tarchi2012}. This certainly complicates being able to predict the AGN properties mostly likely to result in H$_2$O mega-maser emission. Proposed explanations for this occurence include intermediate viewing angle between Sy1 and Sy2, accretion rates within the circumnuclear disk near the Eddington limit, small SMBH masses, and strong molecular outflows fuelled by extreme radiation pressure \citep{tarchi2012}. Despite searches in $\sim 400$ galaxies, no H$_2$O mega-masers have been detected in radio-loud or elliptical galaxies, regardless of AGN type \citep{tarchi2012}.   \subsection{Probing the Unified Model of AGN} \subsection{Circumnuclear H$_2$O mega-masers}  \label{sub:h20_agn}  Circumnuclear H$_2$O mega-masers exhibit  \begin{itemize}  \item greene+2013, Wardle Yusef-zadeh 12, greene+10, schulz henkel 03, tarchi+12  \item these are circumnuclear masers