The Mid-Infrared Colors of the ISM and Extended Sources at the Galactic Center - AstrophysicsReport as inadecuate

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Abstract: A mid-infrared 3.6-8 um survey of the Galactic Center has been carried outwith the IRAC instrument on the Spitzer Space Telescope. This survey covers thecentral 2x1.4 degree ~280x200 pc of the Galaxy. At 3.6 and 4.5 um theemission is dominated by stellar sources, the fainter ones merging into anunresolved background. At 5.8 and 8 um the stellar sources are fainter, andlarge-scale diffuse emission from the ISM of the Galaxy-s central molecularzone becomes prominent. The survey reveals that the 8 to 5.8 um color of theISM emission is highly uniform across the surveyed region. This uniform coloris consistent with a flat extinction law and emission from polycyclic aromatichydrocarbons PAHs. Models indicate that this broadband color should not beexpected to change if the incident radiation field heating the dust and PAHs is<10^4 times that of the solar neighborhood. The few regions with unusually redemission are areas where the PAHs are underabundant and the radiation field islocally strong enough to heat large dust grains to produce significant 8 umemission. These red regions include compact H II regions, Sgr B1, and widerregions around the Arches and Quintuplet Clusters. In these regions theradiation field is >10^4 times that of the solar neighborhood. Other regions ofvery red emission indicate cases where thick dust clouds obscure deeplyembedded objects or very early stages of star formation.

Author: R. G. Arendt 1 and 2, S. R. Stolovy 3, S. V. Ramírez 4, K. Sellgren 5, A. S. Cotera 6, C. J. Law 7 and 8, F. Yusef-Zadeh 7, H. A


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