Two new and remarkable sightlines through the galactic center's molecular gas

Abstract

Until now, the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high-resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r∼180 pc central molecular zone, it is necessary to find additional such sources that cover a much wider longitudinal range of sightlines. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2 in longitude and 0.1 in latitude of Sgr A* using the Spitzer GLIMPSE and the Two Micron All Sky Survey catalogs. Here we present spectra of H+3 and CO toward two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the expanding molecular ring. The spectra toward Sgr B reveal at least 10 absorption components covering over 200kms-1 and by far the largest equivalent width ever observed in an interstellar H +3 line; they appear to provide the first near-infrared view into that hotbed of star formation. © 2010. The American Astronomical Society. All rights reserved..