deletions | additions       diff --git a/h2o_megamasers.tex b/h2o_megamasers.tex  index 8a4216a..2bba3cd 100644  --- a/h2o_megamasers.tex  +++ b/h2o_megamasers.tex 
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\end{equation}  where the impact parameter $b= \theta D$, with $\theta$ being the angular offset from the center of the disk \citep{lo2005}. Since $dV/dt$, $dV/d\theta$ can be measured, one can solve for the distance to the source. This was accomplished for the first time by \citet{Miyoshi_1994}, and is now being used in other systems as a means of measuring the Hubble Constant (\S\ref{sub:h2o_cosmo}).  The modeled rotation curves allow for the masses of the nuclei to be measured.  \citet{wardle2012_bhmass} have derived a model for the formation of these circumnuclear disks around AGN. They argue that impacts of molecular clouds, within some impact parameter, can cause the formation of a thin Keplerian disk. By equating the specific angular momentum at the edge of the disk to that of the material that can just barely be captured by the interaction, they find a relation between the radius of the circumnuclear disk and the mass of the SMBH: $R=4G\lambda^2M/v^2$, where $\lambda$ is the fraction of angular momentum maintained in the interaction, $M$ is the SMBH mass, and $v$ is the initial velocity of the cloud. They find that the relation holds for eight disks with H$_2$O mega-maser emission, largely within observational error. They suggest that the impact of a cloud on one of these disks could create gravitationally unstable episodes, which may potentially give rise to mega-maser emission \citep{Milosavljevi_2004} such that only a fraction host Keplerian circumnuclear disks.  \begin{itemize} 
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% \item weak scintillation model explains observed variability assuming a local screen; distant, strongly scattering screen model fits observations, shows unseen anti-correlation b/w modulation index and timescale  % \end{itemize}  \subsection{Cosmology: Distance Determination} \subsection{Measuring Hubble's Constant}  \label{sub:h2o_cosmo}  \begin{itemize}