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Issue A&A
Volume 430, Number 2, February I 2005
Page(s) 481 - 489
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20040447



A&A 430, 481-489 (2005)
DOI: 10.1051/0004-6361:20040447

Massive star formation in the W49 giant molecular cloud: Implications for the formation of massive star clusters

N. L. Homeier1, 2 and J. Alves1

1  European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching b. München, Germany
2  Johns Hopkins University, Department of Physics and Astronomy, 21218 Baltimore, MD, USA

(Received 15 March 2004 / Accepted 8 September 2004 )

Abstract
We present results from JHKs imaging of the densest region of the W49 molecular cloud. In a recent paper (Alves & Homeier, ApJ, 589, L45), we reported the detection of (previously unknown) massive stellar clusters in the well-known giant radio HII region W49A, and here we continue our analysis. We use the extensive line-of-sight extinction to isolate a population of objects associated with W49A. We constrain the slope of the stellar luminosity function by constructing an extinction-limited luminosity function, and use this to obtain a mass function. We find no evidence for a top-heavy MF, and the slope of the derived mass function is $-1.6 \pm 0.3$. We identify candidate massive stars from our color-magnitude diagram, and we use these to estimate the current total stellar mass of $5{-}7\times10^{4}~M_{\odot}$ in the region of the W49 molecular cloud covered by our survey. Candidate ionizing stars for several ultra-compact HII regions are detected, with many having multipe candidate sources. On the global molecular cloud scale in W49, massive star formation apparently did not proceed in a single concentrated burst, but in small groups, or subclusters. This may be an essential physical description for star formation in what will later be termed a "massive star cluster".


Key words: ISM: $\ion{H}{ii}$ regions -- ISM: bubbles -- Galaxy: open clusters and associations: individual: W49A -- stars: formation -- Galaxy: disk -- infrared: ISM

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© ESO 2005


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