AAS 199th meeting, Washington, DC, January 2002
Session 58. Interstellar Medium - II
Display, Tuesday, January 8, 2002, 9:20am-6:30pm, Exhibit Hall

[Previous] | [Session 58] | [Next]

[58.04] The Chemical Composition at the Edge of the Galaxy

D.A. Lubowich (Hofstra University), J. M. Pasachoff (Hopkins Observatory, Williams College, Williamstown, MA), T. J. Millar, H. Roberts (Dept. of Physics, University of Manchester Institute of Technology, Manchester UK), G. B. Brammer (Hopkins Observatory, Williams College, Williamtown, MA), C. Henkel ((Max-Planck-Institut für Radioastronomie, Bonn, Germany)

We present initial observations to determine the chemical composition of a molecular cloud at the edge of the Galaxy (28 kpc from the Galactic Center). Our observations provide a unique opportunity to determine the chemical composition and physical conditions in 10-Gyr-old less evolved gas similar to the early Galactic disk to help understand the formation of the Galaxy. We used the Kitt Peak 12-m telescope in June 2001 and detected the 2-1 line of CS and the 1-0 lines of HCO+, HCN, and HNC with a peak TR* = 160 mK, 130 mK, 50 mK, and 40 mK respectively. For the 1-0 lines of DNC, DCO+, and N2H+ we obtained upper limits of TR* < 6 mK, 6 mK, and 10 mK respectively. The HCN/HNC ratio indicated that this is a cold cloud with Tkin = 10 K - 20 K. We present additional data from observations of SiO, SO, CH3OH, OCS, H2CO, H2CS, HC3N, CN, C2H, and H2S that will be conducted this fall with the Kitt Peak 12-m and Heinrich Hertz Submillimeter Telescope telescopes. We will test models of Galactic chemical evolution that predict that the abundances of C, N, O will be lower than in any other Galactic cloud and similar to dwarf irregular galaxies. We will test the possibility that we are observing gas from an early burst of massive star formation such as population III halo stars which would have produced some S and O but not a significant amount of the secondary element N that is also produced from low mass stars.

We thank the Research Corporation for providing funding for general community access to Kitt Peak 12-meter telescope, presently operated by Steward Observatory and to the AAS for a small research grant.

[Previous] | [Session 58] | [Next]