deletions | additions       diff --git a/section_OH_Megamasers_label_sec__.tex b/section_OH_Megamasers_label_sec__.tex  index b1d917f..59b5d5d 100644  --- a/section_OH_Megamasers_label_sec__.tex  +++ b/section_OH_Megamasers_label_sec__.tex 
...
There are two observed components of OH mega-masers, diffuse emission on $\sim 100$ pc scales, and parsec scale compact regions. Both of these components appear to only require fairly ordinary conditions \citep{lo2005}. The diffuse component occurs from low-gain, unsaturated masers which amplify continuum emission from the heated, diffuse gas around the galactic nucleus \citep[e.g.]{Baan_1985}. There may be some evidence that this type of OH maser emission may be widespread, and only amplified to mega-maser levels in cases of extreme starbursts. Anomalous galactic OH maser emission has been detected within a parsec of warm-IR star-forming regions which match most of the properties (line ratios, unpolarized) seen in extragalactic mega-masers \cite{Mirabel_1989}. The compact emission regions, in contrast, are thought to have high gains, leading to saturated maser emission \citep[e.g.,]{lonsdale2002}. Each compact source would be an accumulation of a few to many unresolved maser spots, each with narrow linewidths \citet{lo2005}. \citet{Parra_2005} introduced a model capable of accounting for both types within a single gas phase, consistent with gas properties expected in these regions. \citet{randell1995} also show that the 1667 MHz is preferentially amplified for parsec scale clouds with an OH density of $10^4$ cm$^{-3}$ and warm dust ($40-50$ K), which are easily achievable within LIRGs \citep{lo2005}. The case for OH mega-masers not associated with LIRGs is less clear, though cases of these may be related to the systems hosting H$_2$O mega-masers (\S\ref{sec:oh_and_h2o}).  %  Along with the properties explained above, there are some more minor aspects or unique instances that should be mentioned. One detection in the survey of \citet{darling2002_paperIII} shows the first time variable OH mega-maser in IRAS 21272+2514 \citep[$z\sim 0.15$]{darling2002_timevar}. The variation shows maximum flux changes of 34\% the maximum observed flux. Variations are broadband, and the author's state that the modulation timescale is expected to fall within the the maximum timescale measured timescale, 821 days. Variations are also observed in H$_{2}$O megamasers (\S\ref{sub:h2o_props}). (\S\ref{sub:h2o_outflows}). \citet{darling2002_timevar} favour interstellar scintillation as the cause of the variability, however their is claim is tentative and will likely require discovering more sources with this behaviour. Assuming the scintillation model, they constrain the size of the variable source to be smaller than 2 pc, based on the modulation timescales. This is consistent with high-resolution observations of compact masing regions (\S\ref{sub:oh_highres}).  In some of the first detections of OH mega-masers, the line profiles were observed to exhibit extended `wings' in certain velocity features \citep{Baan_1987, Baan_1989}. \citet{Baan_1989} combined the OH maser observations with HI for three systems (III Zw 35, IR 12112+0305, and IC 4553) to confirm the presence of molecular outflows. These outflows are consistent with the velocities of starburst-driven superwinds found in some other active galaxies.  \begin{itemize}  \item typical linewidths   \item multi-velocity emission components  \item trace highly obscured nuclear regions  \item time variability constraints - Darling paper IV  \item 10^5 times more luminous than galactic GMCs (Downs, Solomon 1998)  \item not necessarily amplification of bkg IR radiation  \item line profile wings explained as molecular outflows, starburst winds (Baan haschick 1987, baan haschick henkel 1989)  \end{itemize}  \subsection{Probing Nuclear Regions} 
...
High-resolution studies of several OH mega-masers have been conducted with the VLA, VLBI, and MERLIN. These provide a resolution of a few parsecs with the VLBI, and of order 100 pc with the VLA and MERLIN. These observations allow for the mega-maser sources to be connected with other high-resolution observations taken of the radio continuum and molecular gas (e.g., using CO(2-1) as a tracer). In both Arp 220 and Arp 299, both on-going merger systems, the OH mega-maser emission originates from within 100 pc of the nucleus, where the most intense star formation is occurring \citet{Lonsdale_1994, Baan_1990}. In the case of Arp 299, \citet{Baan_1990} show that the emission originates from a 100 pc rotating structure about the nucleus of IC 694.  \begin{itemize}  \item 10^5 times more luminous than galactic GMCs (Downs, Solomon 1998)  \item not necessarily amplification of bkg IR radiation  \end{itemize}