From dmehring@astro.uiuc.edu Sat Jul  6 13:48:19 1996
From: dmehring@astro.uiuc.edu
Date: Sat, 6 Jul 1996 12:48:14 -0500
To: gcnews@astro.umd.edu

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\begin{document}
\title{44 GHz Methanol Masers and Quasi-Thermal Emission in Sagittarius B2}

\author{David M. Mehringer}
\author{Karl M. Menten } 
\institute{University of Illinois, Department of Astronomy}
\institute{Harvard-Smithsonian Center for Astrophysics}
\begin{abstract}
The Very Large Array has been used to obtain $\sim$3{$^{\prime\prime}$ } resolution
observations on the 44 GHz {\hbox{$7_{0}\to6_{1}A^{+}$}}\ transition of {CH$_3$OH } (methanol) in the
Sgr B2 massive star-forming complex. A total of 18 compact regions showing
maser emission are found, which are spread over a 2.1 pc $\times$ 4.3 pc
($\alpha \times \delta$) region. Many of these are offset far from known
molecular cores and ultracompact HII regions and may trace the interaction
region of a cloud-cloud collision.  There is no spatial coincidence between
44 GHz and 6.7 GHz {CH$_3$OH } masers in this region, as expected because the
pumping mechanisms for these two transitions are different.  Isotropic
maser luminosities range between 1$\times$10$^{-6}$ and
2.1$\times$10$^{-5}$ {L$_\odot$}.  In addition, 17 regions with broad-linewidth
quasi-thermal 44 GHz {CH$_3$OH } emission are identified, many of which are
close to known molecular hot cores, in particular those associated with the
Sgr B2(N) and Sgr B2(M) continuum sources.  In Sgr B2(N), quasi-thermal
emission appears to be associated with two 10{$^{\prime\prime}$ } diameter ionized
shells.  These ionized shells may have swept up and shocked molecular
material as they expanded.  Also, a quasi-thermal core is observed to be
coincident with a source of continuum emission from dust and emission from
more complex species.  In Sgr B2(M), {CH$_3$OH } quasi-thermal emission arises
predominately from the western portion of this region.  The {CH$_3$OH }
fractional abundance in most of the quasi-thermal cores appears to be quite
high at $\sim$10$^{-6}$.  It is argued that grain-surface chemistry is
responsible for this high abundance.
\end{abstract}
\end{document}







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