The Mid-Infrared Colors of the Interstellar Medium and Extended Sources at the Galactic Center

R. G. Arendt(1,2), S. R. Stolovy(3), S. V. Ramírez(4), K. Sellgren(5), A. S. Cotera(6), C. J. Law(7,8), F. Yusef-Zadeh(7), H. A. Smith(9), D. Y. Gezari(10)

(2) Science Systems and Applications, Inc.
(3) Spitzer Science Center
(4) IPAC, California Institute of Technology
(5) Ohio State University
(6) SETI Institute
(7) Northwestern University
(8) Astronomical Institute ``Anton Pannekoek'', University of Amsterdam
(9) Harvard-Smithsonian Center for Astrophysics
(10) NASA/Goddard Space Flight Center

Paper: ApJ, 2008, 682, 384

EPrint Server: 0804.4491


A mid-infrared (3.6 - 8 micron ) survey of the Galactic Center has been carried out with the IRAC instrument on the Spitzer Space Telescope. This survey covers the central 2\arcdeg *1.^o4 ( 280* 200 pc) of the Galaxy. At 3.6 and 4.5 micron the emission is dominated by stellar sources, the fainter ones merging into an unresolved background. At 5.8 and 8 micron 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 8 to 5.8 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). Models indicate that this broadband color should not be expected to change if the incident radiation field heating the dust and PAHs is < 104 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 dust grains to produce significant 8 micron emission. These red regions include compact H II regions, Sgr B1, and wider regions around the Arches and Quintuplet Clusters. In these regions the radiation field is > 104 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.

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

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