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First Glimpse Results on the Stellar Structure of the Galaxy
journal contributionposted on 2023-05-16, 17:47 authored by Benjamin, RA, Churchwell, E, Babler, BL, Indebetouw, R, Meade, MR, Whitney, BA, Watson, C, Wolfire, MG, Wolff, MJ, Ignace, R, Bania, TM, Bracker, S, Clemens, DP, Chomiuk, L, Cohen, M, John DickeyJohn Dickey, Jackson, JM, Kobulnicky, HA, Mercer, EP, Mathis, JS, Stolovy, SR, Uzpen, B
The GLIMPSE (Galactic Legacy Mid-Plane Survey Extraordinaire) Point Source Catalog of ∼30 million mid-infrared sources toward the inner Galaxy, 10° ≤ |l| ≤ 65° and |b| ≤ 1°, was used to determine the distribution of stars in Galactic longitude, l, latitude, b, and apparent magnitude, m. The counts versus longitude can be approximated by the modified Bessel function N = N 0(l/l 0) K 1,(l/l 0), where l 0 is insensitive to limiting magnitude, band choice, and side of Galactic center: l 0 = 17°-30° with a best-fit value in the 4.5 μm band of l 0 = 24° ± 4°. Modeling the source distribution as an exponential disk yields a radial scale length of H* = 3.9 ± 0.6 kpc. There is a pronounced north-south asymmetry in source counts for |l| ≲ 30°, with ∼25% more stars in the north. For l = 10°-30°, there is a strong enhancement of stars of m = 11.5-13.5 mag. A linear bar passing through the Galactic center with half-length R bar = 4.4 ± 0.5 kpc, tilted by φ = 44° ± 10° to the Sun-Galactic center line, provides the simplest interpretation of these data. We examine the possibility that enhanced source counts at l = 26°-28°, 31°.5-34°, and 306°-309° are related to Galactic spiral structure. Total source counts are depressed in regions where the counts of red objects (m K- m [8.0] > 3) peak. In these areas, the counts are reduced by extinction due to molecular gas, high diffuse backgrounds associated with star formation, or both.
Publication titleThe Astrophysical Journal
Department/SchoolSchool of Natural Sciences
PublisherThe University of Chicago Press
Place of publicationChicago, USA