Subject: GCFLASH - Vol. 5, No. 9 (Jul 14, 1997) ======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@astro.umd.edu http://www.astro.umd.edu/~gcnews ======================================================================== Vol. 5, No. 9 Jul 14, 1997 This is the last Newsflash of this volume. Volume 5 of GCNEWS is now finished and will be made public within the next two days. Of course, we welcome any abstracts submitted for Vol. 6 of GCNEWS. Recently submitted papers: -------------------------- 1.) Molecular Gas in the Galactic Center Region II. The Large Scale Structure and Physics based on a C^18O(J = 1 -> 0) Survey (Dahmen et al., A&A) 2.) The Origin of the High-Energy Activity at the Galactic Center (Yusef-Zadeh et al., 4th Compton Symp.) ------------------------------------------------------------------------ Email : G.Dahmen@qmw.ac.uk Title : Molecular Gas in the Galactic Center Region II. The Large Scale Structure and Physics based on a C^18O(J = 1 -> 0) Survey Author(s): G. Dahmen(1,3), S. Huettemeister(2,4,1), T.L. Wilson(1) Institute: (1) Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn, Germany, (2) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A., (3) Physics Department, Queen Mary & Westfield College, University of London, Mile End Road, London E1 4NS, England (4) Radioastronomisches Institut, Universitaet Bonn, Auf dem Huegel 71, 53121 Bonn, Germany Paper : submitted to A&A Weblink : http://www-star.qmw.ac.uk/~dahmen/C18O_Paper_II.html Abstract: The large scale structure and physics of molecular gas in the Galactic center region is discussed based on the detailed analysis of a 9' resolution survey of the Galactic center region in the J = 1 -> 0 line of C^18O. Emphasis is placed on the comparison with ^12CO(1-0) data. The line shapes of C^18O(1-0) and ^12CO(1-0) differ significantly. The ratio of the intensities of the two isotopomers in the Galactic center region is generally higher than the value of ~ 15 expected from the ``Standard Conversion Factor'' (SCF) of ^12CO integrated line intensity to H_2 column density. In the 9'-beam, this ratio is in the range from 30 to 200, mostly ~ 60 to 80. From LVG calculations, we estimate that the large scale ^12CO(1-0) emission in the Galactic center region is of moderate (tau >~ 1) or low optical depth (tau < 1). Higher optical depths (tau >= 10) are restricted to very limited regions such as Sgr B2. In addition, we estimate H_2 densities and kinetic temperatures for different ranges of intensity ratios. A considerable amount of molecular mass is in a widespread molecular gas component with low densities and high kinetic temperatures. From our C^18O measurements and from results based on dust measurements, the total molecular mass is found to be (3^+2_-1) * 10^7 M_o. We show that the SCF is not valid toward the Galactic bulge. It overestimates the H_2 column density by an order of magnitude because the assumptions required for this factor of optically thick ^12CO emission and virialization of the molecular clouds are not fulfilled for a significant fraction of the molecular gas. Therefore, one can also not apply a modified conversion factor to the Galactic center region since the ^12CO luminosity is not directly related to the H_2 mass. A comparison with results from bulge regions of external galaxies indicates that the ^12CO emission is generally not a suitable tracer of H_2 masses in the central regions of galaxies. ------------------------------------------------------------------------ Email : ZADEH@OSSENU.ASTRO.NWU.EDU Title : The Origin of the High-Energy Activity at the Galactic Center Author(s): Farhad Yusef-Zadeh(1), William Purcell(1), & Eric Gotthelf(2) Institute: (1) Dept. Physics and Astronomy, Northwestern University, Evanston, Ill. 60208, (2) NASA/GSFC, Greenbelt, MD 20771 Paper : To be published in Proc. of 4th Compton Symp., Weblink : http://www.astro.nwu.edu/astro/faculty/farhad/papers.html Abstract: Recent X-ray and gamma-ray observations of the Galactic center region by the ASCA and CGRO/EGRET instruments show evidence of 2-10 keV and >1 GeV continuum emission as well as 6.7 and 6.4 keV line emission from the inner 0.2^o of the Galactic center. This region is also known to host a bright nonthermal radio continuum source Sgr A East and a dense molecular cloud M-0.02-0.07 known as the 50 km s^-1 cloud. The oval-shaped nonthermal Sgr A East is physically interacting with M-0.02-0.07 at the Galactic center. A comparison between the distribution of ionized, synchrotron and neutral gas suggests a self-consistent interpretation of the high-energy activity at the Galactic center. Our preliminary analysis of the data suggest a shock model of cosmic ray acceleration at the site of the interaction to explain the enhanced GeV gamma-ray emission. We also address a number of issues related to the spatial correlation of the diffuse radio and X-ray emitting gas as well as to the origin of the fluorescent 6.4 and 6.7 keV emission at the Galactic center. ------------------------------------------------------------------------ (Older versions of the Newsflash can be found at the gcnews web-page) ======================================================================== Edited by Angela Cotera Heino Falcke (cotera@ipac.caltech.edu) (hfalcke@astro.umd.edu) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - For Abstract submission please send the (La)Tex file of your paper to gcnews@astro.umd.edu ========================================================================