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Astron. Astrophys. 358, 521-534 (2000)

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The radial distribution of OB star formation in the Galaxy *

L. Bronfman 1, S. Casassus 1,2, J. May 1 and L.-Å. Nyman 3,4

1 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
2 Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
3 SEST, ESO-La Silla, Casilla 19001, Santiago 19, Chile
4 Onsala Space Observatory, 43992 Sweden

Received 6 January 1999 / Accepted 28 February 2000


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 [FORMULA] within the range [FORMULA] in galactocentric radius. We find 492 massive star forming regions within the solar circle, producing [FORMULA] 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 [FORMULA] and of [FORMULA], respectively. Massive star formation is distributed in a layer with its centroid [FORMULA] following that of molecular gas for all galactocentric radii, both north and south. Its thickness for [FORMULA] is [FORMULA] pc (FWHM), [FORMULA] the thickness of the molecular gas disk. The FIR luminosity produced by massive stars has a well defined maximum at [FORMULA], with a gaussian FWHM of [FORMULA]- compared with [FORMULA] 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 [FORMULA], compared with [FORMULA] for the H2 surface density. Massive star formation per unit H2 mass is maximum for [FORMULA] in the southern Galaxy, with a FIR surface luminosity to H2 surface density ratio of [FORMULA], compared with [FORMULA] at the same radius in the north, and with an average of [FORMULA] for the whole galactic disk within the solar circle.

Key words: Galaxy: structure – infrared: ISM: continuum – ISM: clouds – ISM: H ii regions – ISM: molecules – infrared: ISM: continuum

* Based partly on results collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: L. Bronfman

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© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000