st ro - p h / 05 07 46 3 v 1 1 9 Ju l 2 00 5 Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H

Using an absorption line from the metastable (J , K) = (3, 3) level of H3 together with other lines of H3 and CO observed along several sightlines, we have discovered a vast amount of high temperature (T ∼ 250 K) and low density (n ∼ 100 cm) gas with a large velocity dispersion in the Central Molecular Zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately threefourths of the H3 along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H3 located in intervening spiral arms. About half of H3 in the CMZ has velocities near ∼ −100 km s indicating that it is associated with the 180 pc radius Based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). Based on data collected at the United Kingdom Infrared Telescope, which is operated by the Joint Astronomy Centre on behalf of the U. K. Particle Physics and Astronomy Research Council. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. 4 Department of Astronomy and Astrophysics, and Department of Chemistry, The Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 USA Gemini Observatory, Hilo, Hawaii 96720 USA Max Planck Institute for Astronomy, Heidelberg, Germany Subaru Telescope, National Astronomical Observatory of Japan, Hilo, Hawaii 96720 USA 8 Department of Chemistry and Department of Astronomy, University of Illinois Urbana-Champaign, Urbana, IL 61801-3792 USA