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 \documentstyle{article} \textwidth 18cm \textheight 23cm \oddsidemargin -1cm \topmargin 0cm \parskip 0.15cm \parindent 0pt \small \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} ----- End Included Message -----