STAR FORMATION IN MASSIVE CLUSTERS VIA THE WILKINSON MICROWAVE ANISOTROPY PROBE AND THE SPITZER GLIMPSE SURVEY

Journal Article · Wed Jan 20 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/709/1/424· OSTI ID:21392339

Murray, Norman ^[1]; Rahman, Mubdi ^[2]

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1. Canadian Institute for Theoretical Astrophysics, 60 St. George Street, University of Toronto, Toronto, ON M5S 3H8 (Canada)
2. Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4 (Canada)

We use the Wilkinson Microwave Anisotropy Probe (WMAP) maximum entropy method foreground emission map combined with previously determined distances to giant H II regions to measure the free-free flux at Earth and the free-free luminosity of the Galaxy. We find a total flux f{sub n}u = 54, 211 Jy and a flux from 88 sources of f{sub n}u = 36, 043 Jy. The bulk of the sources are at least marginally resolved, with mean radii approx60 pc, electron density n{sub e} approx 9 cm{sup -3}, and filling factor PHI{sub H{sub I{sub I}}}approx0.005 (over the Galactic gas disk). The total dust-corrected ionizing photon luminosity is Q = 3.2 x 10{sup 53} +- 5.1 x 10{sup 52} photons s{sup -1}, in good agreement with previous estimates. We use GLIMPSE and Midcourse Space Experiment (MSX) 8 mum images to show that the bulk of the free-free luminosity is associated with bubbles having radii r approx 5-100 pc, with a mean of approx20 pc. These bubbles are leaky, so that ionizing photons emitted inside the bubble escape and excite free-free emission beyond the bubble walls, producing WMAP sources that are larger than the 8 mum bubbles. We suggest that the WMAP sources are the counterparts of the extended low density H II regions described by Mezger. The 18 most luminous WMAP sources emit half the total Galactic ionizing flux. These 18 sources have 4 x 10{sup 51} s{sup -1} approx< Q approx< 1.6 x 10{sup 52} s{sup -1}, corresponding to 6 x 10{sup 4} M{sub sun} approx< M{sub *} approx< 2 x 10{sup 5} M{sub sun}; half to two thirds of this will be in the central massive star cluster. We convert the measurement of Q to a Galactic star formation rate (SFR) M-dot{sub *}=1.3+-0.2 M{sub sun} yr{sup -1}, where the errors reflect only the error in free-free luminosity. We point out, however, that our inferred M-dot{sub *} is highly dependent on the exponent GAMMA approx 1.35 of the high-mass end of the stellar initial mass function. For 1.21 < GAMMA < 1.5, we find 0.9 M{sub sun} yr{sup -1} < M-dot{sub *} < 2.2 M{sub sun} yr{sup -1}. We also determine a SFR of 0.14 M{sub sun} yr{sup -1} for the Large Magellanic Cloud and 0.015 M{sub sun} yr{sup -1} for the Small Magellanic Cloud.

• OSTI ID: 21392339
• Journal Information: Astrophysical Journal, Vol. 709, Issue 1; Other Information: DOI: 10.1088/0004-637X/709/1/424; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ANISOTROPY
CALCULATION METHODS
DUSTS
ELECTRON DENSITY
ENTROPY
LUMINOSITY
MAGELLANIC CLOUDS
MASS
MICROWAVE RADIATION
PHOTON EMISSION
PHOTONS
STAR CLUSTERS
STARS
BOSONS
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EMISSION
GALAXIES
MASSLESS PARTICLES
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
THERMODYNAMIC PROPERTIES