R. G. Arendt (1, 2), S. R. Stolovy (3), S. V. Ramirez (4), K. Sellgren (5), A. S. Cotera (6), C. J. Law (7, 8), F. Yusef-Zadeh (7), H. A. Smith (9), and D. Y. Gezari (10)
ApJ, submitted, October 4, 2007
A mid-infrared (3.6 - 8 microns) survey of the Galactic Center has been carried out with the IRAC instrument on the Spitzer Space Telescope. This survey covers the central 2 x 1.4 degrees (~280 x 200 pc) of the Galaxy. At 3.6 and 4.5 microns the emission is dominated by stellar sources, the fainter ones merging into an unresolved background. At 5.8 and 8 microns the stellar sources are fainter, and large-scale diffuse emission from the ISM of the Galaxy's central molecular zone becomes prominent. The survey reveals that the 5.8 to 8 micron color of the ISM emission is highly uniform across the surveyed region. This uniform color is consistent with a flat extinction law and emission from polycyclic aromatic hydrocarbons (PAHs) excited by an interstellar radiation field that is less than 10,000 times that of the solar neighborhood. The few regions with unusually red emission are areas where the PAHs are underabundant and the radiation field is locally strong enough to heat large grains to produce significant 8 micron emision. These red regions include compact H II regions, wider regions around the Arches and Quintuplet Clusters, and Sgr B1. In these regions the radiation field is greater than or about 10,000 times that of the solar neighborhood. Other regions of very red emission indicate cases where thick dust clouds obscure deeply embedded objects or very early stages of star formation.
(1) CRESST/UMBC/GSFC, Code 665, NASA/Goddard Space Flight Center, USA
(2) Science Systems and Applications, Inc., USA
(3) Spitzer Science Center, California Institute of Technology, USA
(4) IPAC, California Institute of Technology, USA
(5) Astronomy Department, Ohio State University, USA
(6) SETI Institute, USA
(7) Department of Physics and Astronomy, Northwestern University, USA
(8) Astronomical Institute "Anton Pannekoek", University of Amsterdam,
The Netherlands
(9) Harvard-Smithsonian Center for Astrophysics, USA
(10) NASA/Goddard Space Flight Center, USA
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Revised: 2007 October 4 (ks)