The Infrared Galaxy
201351 pages
Published in:
- Planets, Stars and Stellar Systems, 5: Galactic Structure and Stellar Populations
- Published: 2013 in Netherlands by Springer
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Abstract:
As infrared surveys have reached optical-quality angular resolution, they have revealed new information on the stellar, interstellar, and star-formation components of the Galaxy. The distance to the Galactic center appears to be known to within 5%: R = 8. 0 0. 4 kpc. Measurements of the stellar scalelength of the disk, R = 2–4 kpc, continue to show a large range; the origin of this scatter needs to be understood. The exponential disk does not continue into the center of the Galaxy, with an inner radius of R ∼ 3 kpc. Claims exist for a truncation, or change in scalelength, in the outer disk, but are not yet confirmed. The stellar disk is warped, with a similar nonsymmetric azimuthal dependence as the HI disk, but a lower amplitude and uncertain radial extent. There is extensive evidence for two non-axisymmetric structures in the inner galaxy: the Galactic bar (or triaxial bulge) and the Long Bar, which differ in angle by ∼ 20. The existence of an inner (nuclear) bar seems likely, but studies have not converged on its parameters. There is no compelling evidence for a ring in stellar mass, but a case can be made for a star-forming ring. These surveys have also revealed the projected Galactic distribution of interstellar dust and shed light on the extinction and radiation properties of dust in different Galactic environments. We review the spatial distribution and wavelength dependence of extinction, the distribution and magnitude of PAH emission and stochastic and thermal dust emission, and different stages of massive star formation, e.g., infrared dust clouds (IRDCs), IR bubbles around HII regions, extended green objects (EGOs), and massive star formation regions, including evidence for triggered star formation. We briefly discuss what infrared observations tell us about evolved stars, including variable stars, asymptotic giant stars (AGB), planetary nebulae (PNe), Luminous Blue Variables (LBVs) and Wolf-Rayet stars, and supernova remnants. We end with a comparison of the limitations of optical, infrared, and radio surveys of the Galaxy that should be borne in mind.References(205)
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