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E. T. Chambers, J. M. Rathborne, J. M. Jackson (Boston University), R. Simon (Universitat zu Koln)
We have found evidence for active star formation in compact millimeter cores within Infrared Dark Clouds (IRDCs). IRDCs were discovered by the ISO and MSX infrared surveys as extinction features in the mid-infrared. We examined 42 of the highest extinction IRDCs in the millimeter continuum to search for compact cores and found that these IRDCs invariably contain at least one such core, and many contain several. These cores have sizes and masses of ~ 0.5 pc and 100-1000 Msun. Roughly one third of these cores show evidence for active star formation including (1) enhanced, slightly extended emission at 4.5 microns which might arise from shocked H2, (2) broad line widths (delta v ~ 10 km s-1) of HCN(4-3) and CS(3-2), and the detection of SiO(2-1), a well-known shock tracer, and (3) bright, compact 24 micron emission that indicates a deeply embedded protostar. The large number of active cores we find toward IRDCs suggests that IRDCs are indeed the earliest stages in the evolution of star-forming molecular clumps. Here we present Spitzer/IRAC three-color images, Spitzer/MIPS 24 micron images and molecular line emission toward both active and quiescent cores.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.