deletions | additions       diff --git a/section_OH_Megamasers_label_sec__.tex b/section_OH_Megamasers_label_sec__.tex  index 6c821f8..e7baa52 100644  --- a/section_OH_Megamasers_label_sec__.tex  +++ b/section_OH_Megamasers_label_sec__.tex 
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% 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_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}). XXX Lonsdale et al variability in Arp 220 XXX  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}. \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  
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\subsection{Probing Nuclear Regions}  \label{sub:oh_highres}  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}. \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) 
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\cite{Darling_2007} extended this search by exploring the connection between star formation rate (calculated from IR luminosity) and the line luminosity of CO. A linear relationship exists between the IR and CO luminosities for star-forming galaxies over many orders of magnitude \citep{Gao_2004}. \citet{Darling_2007} finds the OH mega-maser hosts break this linear trend XXX FIGURE XXX, suggesting that the hosts of OH mega-masers are undergoing a special triggered star formation event due to the merger.  Further differences between the OH mega-maser hosts and LIRGs without maser emission were found by \citet{willett2011_I, willett_2011_II}. \citet{willett2011_I,willett_2011_II}.  In these two papers, the authors use Spitzer IRS spectroscopy to study LIRGs and ULIRGs that were part of the \citet{darling2002_paperIII} survey, both detections and non-detections. The medianed spectra of all sources is shown in Figure \ref{fig:oh_IR_spectra}. There is a clear difference between the galaxies with and without OH mega-masers. Notably, hosts of OH mega-masers show deeper absorption features near 10 and 18 $\mu$m, and the slope at longer wavelengths is steeper. \citet{ivezic1997} show that these are features due to an increase in dust opacity. This also shifts the peak of the IR emission to a maximum between 35-53$\mu$m, which is likely the pumping mechanism for the OH masers \citep{darling2012}. By also comparing with a dense gas tracer, HCN, \citet{Darling_2007} finds a high dense molecular gas fraction, L$_{\mathrm{HCN}}$/L$_{\mathrm{IR}} \gt 0.07$...