Dense molecular clumps associated with young clusters in massive star-forming regions.
SAITO H., SAITO M., SUNADA K. and YONEKURA Y.
Abstract (from CDS):
We present the results of C18O observations by the 45 m Nobeyama radio telescope toward dense clumps with young clusters in nine massive star-forming regions. We identified 39 clumps whose mass, radius, and line width range from 15 to 1500 M☉, from 0.14 to 0.76 pc, and from 0.6 to 3.2 km/s, respectively. The clumps associated with massive (proto)stars have a large line width (∼2.5 km/s) and a large mass (∼500 M☉). Most of the clumps are sufficiently gravitationally bound because they have a virial mass similar to the gas mass, and the average H2density of the clumps increases with increasing internal kinetic motion. Next, we found two relations, one between the number density of associated 2MASS sources and the average H2density of the clump and the other between the number density of sources and the star formation efficiency of the clump. From these results, we suggest that a structure, whose size scale is ∼0.3 pc, with a high average H2density is required in order for cluster formation to occur. In addition, we found that the internal kinetic motion of a clump has to be large in order to form massive stars, because there is a good correlation between the maximum mass of associated stars and the line width of the clump. Such clumps with large internal motion must generally have a high average H2density in order to be gravitationally bound. Thus, massive stars are formed in a dense cluster.