The southern star forming region NGC 3603 is considered a galactic pendent to extragalactic starburst regions, with the great advantage of being comparatively nearby and only moderately obscured by foreground material. It consists of a stellar cluster harboring numerous high mass stars and thousands of intermediate to low-mass stars, and a giant HII region which is propagating into the parent giant molecular cloud.
Deep Ks-band observations of the cluster have been performed with the ESO Very Large Telescope, demonstrating that the Ks-band luminosity function (KLF, for radii <30 arcsec) is rising down to Ks ∼17.0 to 17.5 mag (∼0.5 Msun at a cluster age of 1 Myr), suggesting that there is no lower mass cut-off of the stellar mass function in that starburst cluster. The slope of the KLF is consistent with a Miller-Scalo type initial mass function (IMF) of a ∼1 Myr old stellar cluster.
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| Figure: The area around the NGC3603 cluster as seen at near-infrared (left, Ks, VLT ISAAC) and at mid-infrared wavelengths (right, 11.9μm, TIMMI2, ESO 3.6m). Whereas the NIR image allows a detailed examination of the stellar population of the cluster, the MIR image shows the distribution of warm dust (few hundred K) in the interaction zone between the energetic radiation from the OB cluster and the surrounding cloud, in the immediate vicinity of the high-mass protostar IRS9, and in a population of faint sources in the cluster itself, proposed to be ``proplyd''-like externally heated circumstellar dust disks |
In addition, we performed the first wide-field subarsec resolution study of the cluster and its parent GMC, revealing a wide variety of point-like and extended mid-infrared (MIR) sources, which generally indicates the presence of warm (few hundred K) dust (i.e., circumstellar disks or envelopes, PDRs heated by hot OB stars). Extensive areas of partly diffuse, partly highly structured MIR emission indicate PDRs where the expanding HII region is interacting with the parent giant molecular cloud. We have identified a cluster of newly forming young stellar objects, the most luminous being IRS 9, which is (contrary to previous work) the MIR point source clearly dominating the area, very likely a high-mass protostar which has been made visible through the action of winds and radiation from the NGC 3603 starburst cluster. Clearly, high mass star formation is going on in this GMC. A number of fainter point sources, generally associated with stars of B or late O type, show that intermediate to high mass star formation is still going on at a moderate level in many parts of the GMC. Finally we found a population of faint MIR sources in the starburst cluster itself. In addition the MIR counterparts to Wolf-Rayet stars in the cluster we suggest that we see a population of comparably low-mass stars, surrounded by circumstellar disks, which are externally heated by the hot massive cluster stars, rendering them visible at MIR wavelengths. These objects would be the first examples of ``proplyds'' found in HII regions other than the Orion Nebula, demonstrating that circumstellar disks -- the progenitors of planetary systems -- can even survive for some time in the harsh environment of a starburst cluster.
⇒ Nürnberger & Petr-Gotzens (2002); Nürnberger et al. (2002)