Astronomy and Astrophysics, volume 358, 521-534 (2000/6-2)
The radial distribution of OB star formation in the Galaxy.
BRONFMAN L., CASASSUS S., MAY J. and NYMAN L.-A
Abstract (from CDS):
We present the azimuthally averaged radial distribution of 748 regions of OB star formation in the whole galactic disk, based on our previous CS(2-1) survey of UC H II regions. Embedded massive stars produce a total FIR luminosity of 1.39x108L☉ within the range 0.2≤R/R0≤2 in galactocentric radius. We find 492 massive star forming regions within the solar circle, producing 81% of the total FIR luminosity. Separate analyses of the 349 sources in the I and II quadrant (north), and of the 399 sources in the III and IV quadrant (south), yield FIR luminosities (extrapolated to the complete galactic disk) of 1.17x108L☉ and of 1.60x108L☉, respectively. Massive star formation is distributed in a layer with its centroid Z0(R) following that of molecular gas for all galactocentric radii, both north and south. Its thickness for R≤R0 is ∼73pc (FWHM), 62% the thickness of the molecular gas disk. The FIR luminosity produced by massive stars has a well defined maximum at R=0.55R0, with a gaussian FWHM of 0.28R0- compared with 0.51R0 for the H2 surface density distribution. Toward the outer Galaxy, down from the maximum, the face-on FIR surface luminosity decays exponentially with a scale length of 0.21R0, compared with 0.34R0 for the H2 surface density. Massive star formation per unit H2 mass is maximum for R∼0.55R0 in the southern Galaxy, with a FIR surface luminosity to H2 surface density ratio of ∼0.41L☉/M☉, compared with ∼0.21L☉/M☉ at the same radius in the north, and with an average of ∼0.18L☉/M☉ for the whole galactic disk within the solar circle.
Galaxy: structure - infrared: ISM: continuum - ISM: clouds - ISM: HII regions - ISM: molecules - infrared: ISM: continuum
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