The Molecular Gas in the Galactic Center Region based on C^18O Measurements, Presentation of a Large Scale J=1-0 Survey obtained with the 1.2m Southern Millimeter-Wave Telescope at CTIO

G. Dahmen(1,2), S. Hüttemeister(3,1), T.L. Wilson(1), R. Mauersberger(4,1), A. Linhart(1), L. Bronfman(5), A.R. Tieftrunk(1), K. Meyer(1), W. Wiedenhöver(1), T.M. Dame(3), E.S. Palmer(3), J. May(5), J. Aparici(5), F. Mac-Auliffe(5)

(1) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
(2) Physics Department, Queen Mary & Westfield College, University of London, Mile End Road, London E1 4NS, U.K.
(3) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.
(4) Steward Observatory, The University of Arizona, Tucson, AZ 85716, U.S.A.
(5) Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago de Chile, Chile

Paper: to appear in the Proceedings of the 4th ESO/CTIO Workshop on ``The Galactic Center''



A large scale C^18O(J=1-0) survey of the central few hundred pc (-1.05^o <= l <= +3.6^o, -0.9^o <= b <= +0.75^o) of the Galaxy is presented. These 9^' resolution data were obtained with the 1.2 m Southern Millimeter-Wave Telescope (SMWT) at CTIO and compared to ^12CO(1-0) data also obtained with this telescope. In addition, HNCO(5_0,5-4_0,4) line data included in the spectrometer passband are also presented. Although both ^12CO and C^18O are thought to be tracers of the molecular mass, their distribution and line shapes differ significantly. The C^18O(1-0) line is mucher weaker than expected from the ``Standard I_^12CO(1-0)/N_H_2 Conversion Formula'' obtained by Strong et al. (1988). LVG calculations suggest that on large scales the ^12CO(1-0) emission is only of intermediate ( tau = 1 - 5) or low optical depth ( tau < 1). In this case, the ``Standard Conversion Formula'' overestimates N_H_2. Our C^18O(1-0) data combined with other H_2 tracers indicate a total molecular mass of (3^+2_-1) * 10^7 M_o. The existence of a widespread component of molecular gas with low density (thin gas) is found to be very likely.

Preprints available from the authors at , or the raw TeX (no figures) if you click here.

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