Subject: GCFLASH - Vol. 3, No. 10 (Oct 15, 1996) ======================================================================== G C N E W S * Newsflash * - The Newsletter for Galactic Center Research - gcnews@astro.umd.edu http://www.astro.umd.edu/~gcnews ======================================================================== Vol. 3, No. 10 Oct 15, 1996 Recently submitted papers: -------------------------- 1) Compact Radio Cores in the Galactic Center and Elsewhere (Falcke, IAU Coll. 163) 2) SiO emission from the Galactic Center Molecular Clouds (Martin-Pintado et al., ApJ Letters) ------------------------------------------------------------------------ Email : hfalcke@astro.umd.edu Title : Compact Radio Cores in the Galactic Center and Elsewhere Author(s): Heino Falcke Institute: Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA (hfalcke@astro.umd.edu) Paper : review, to appear in: IAU Coll. 163, ``Accretion Phenomena and Related Outflows'', Wickramasinghe D., Ferrario L., Bicknell G. (eds.), PASP Conf. Proc. Weblink : http://www.astro.umd.edu/~hfalcke/publications.html#iauc163 EPrint : astro-ph/9610098 Abstract: Compact radio cores are not only common in radio galaxies and quasars but also in many nearby galaxies with low-active, supermassive black holes. One famous example is the Galactic Center source Sgr A*. Recent studies of proper motions and radial velocities of stars in the inner parsec of the Galaxy convincingly demonstrate the presence of a compact dark mass of 2.5 * 10^6 M_o in the nucleus of the Milky Way. Millimeter VLBI and submm observations of Sgr A* thus probe a region of only a few Schwarzschild radii in diameter. In this paper I will review our current theoretical and observational knowledge of this source and compare it to some famous LINER galaxies like NGC 4258, NGC 3079, and NGC 6500. In all cases these radio cores can be well explained by a standard AGN jet model, and, with the exception of Sgr A*, large scale outflows are observed that have powers comparable to those inferred from the radio cores. Recent VLBI observations of radio-weak quasars and HST observations of Seyfert galaxies indicate that these AGN also produce powerful jets which, however, have relatively less luminous radio cores than radio-loud quasars and the LINERs discussed here. Therefore, jets and compact radio cores appear to be natural constituents of an AGN, but the reason why apparently some jets are radio-loud and others not remains a mystery. ------------------------------------------------------------------------ Email : martin@oan.es Title : SiO emission from the Galactic Center Molecular Clouds Author(s): J. Martin-Pintado, P. de Vicente, A. Fuente, P. Planesas Institute: Observatorio Astronomico Nacional (IGN), Campus Universitario, Apartado 1143, E-28800 Alcala de Henares, Spain Paper : accepted for ApJ Letters Abstract: We have mapped the J=1->0 line of SiO in a 1 DEG x 12 ARCMIN (l*b) region around the Galactic center (GC) with an angular resolution of 2' (~ 4 pc). In contrast to the spatial distribution of other high dipole moment molecules like CS, whose emission is nearly uniform, the SiO emission is very fragmented and it is only associated with some molecular clouds. In particular, it is remarkable that the SiO emission closely follows the non-thermal radio arc in the GC. The SiO clouds are more extended than the beam with typical sizes between 4 and 20 pc. High angular resolution (26') mapping in the J=2->1 line of SiO toward the molecular clouds in Sgr B2 and Sgr A shows that the SiO emission is relatively smooth with structures of typically 2 pc. From the line intensities of the J=2->1, J=3->2 and J=5->4 transitions of SiO we derive H_2 densities for these clouds of a few 10^4 cm^-3. The SiO fractional abundances are ~10^-9 for the SiO clouds and <~10^-10 for the other molecular clouds in the GC. The characteristics (size and H_2 densities) of the SiO emission in the GC are completely different from those observed in the Galactic disk, where the SiO emission arises from much smaller regions with larger H_2 densities. We briefly discuss the implications of the SiO emission in the molecular clouds of the GC. We conclude that the particular chemistry in these clouds is probably related to large scale fast shocks occurring in the Galactic center region. ------------------------------------------------------------------------ (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 ========================================================================