deletions | additions       diff --git a/introduction.tex b/introduction.tex  index b5425e6..d2c5ead 100644  --- a/introduction.tex  +++ b/introduction.tex 
...
In this report, I focus on the discovery, mechanisms, and applications of mega-masers. Until recently, mega-maser emission had only been confidently detected from three species: OH, H$_2$O, and H$_2$CO. The vast majority of the detected mega-maser detection arises from the 22 GHz XXX transition XXX H$_2$O transition XXX and the primary hyperfine ground-state OH lines (1665 \& 1667 MHZ) XXX. Mega-masers were first detected by \citet{DOS_SANTOS_1979}, who found 22 GHz H$_2$O emission towards the nucleus of NGC 4945. They inferred an isotropic luminosity $~10^6$ times greater than any known galactic maser source, leading to the term "mega"-maser. \citet{Baan_1982} reported the first OH mega-maser towards the peculiar galaxy IC 4553. XXX have also detected mega-maser emission from the H$_2$O XXX transition. \citet{baan1986} reported the lone detection of a formaldehyde (H$_2$CO) mega-maser in the 1$_{10}$-1$_{11}$ (6.2 cm) transition. Recent results by, \citet{wang2014} and \citet{chen2015} have extended the mega-masing species to five with their detection of six transitions in methanol (CH$_3$OH; 36.2 GHz, 37.7 GHz, and four clustered at 96.7 GHz), and the silicon monoxide (SiO) J=2-1 ($v=3$) transition.   XXX Tie in better with rest of intro XXX  The high surface-brightness of the compact maser sources make most mega-masers excellent VLBI targets to a limit of $\sim 10$ mJy per beam size (see \S\ref{sec:h2o_mm}). Most VLBI observations show that the majority of the flux is recovered using the VLBI, confirming that most mega-maser emission occurs within compact regions \citep{lo2005}. XXX  This report is arranged as follows. Section \ref{sec:maser_theory} presents the basics of Maser Theory, deriving expressions for the line intensity as a function of path length in the unsaturated and saturated regimes. Section \ref{sec:OH} presents the observational results and applications of OH megamaser emission, while Sections \ref{sec:H2O} and \ref{sec:others} present the same for H$_2$O and other detected megamasers, respectively. Section \ref{sec:conclusion} discusses the use of future surveys using the upcoming generation of radio telescopes.  \begin{itemize}