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

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 ([CITE], 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 . We identify candidate massive stars from our color–magnitude diagram, and we use these to estimate the current total stellar mass of 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”.