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S.J. Carey (Boston College), P.A. Feldman, R.O. Redman (NRC/Canada), M.P. Egan (AFRL), D. Mizuno, T. Kuchar (BC), S. Price (AFRL)
The Midcourse Space Experiment (MSX) infrared-dark clouds (IRDCs) are a population of a few thousand molecular cores that have been identified by their substantial mid-infrared (8-25 \mum) extinctions in the MSX Galactic Plane survey images (Egan et al. 1998, ApJL, 494, L199). Subsequent observations have revealed IRDCs to contain cold (T < 15 K), dense (n ~ 106 cm-3) molecular gas (Carey et al. 1998, ApJ, 508, 721). The IRDCs are distributed along spiral arms and are located near but do not contain star formation tracers such as HII regions and H2O maser emission. Continuum maps at 450 and 850 \mum taken with SCUBA on the JCMT reveal bright knots of emission within the envelope of emission associated with the IRDCs. Many IRDCs are filamentary in nature. The bright emission knots have HCO+ and CO line profiles indicative of outflow and/or infall with several sources exhibiting the blue-red asymmetry characteristic of infall. The IRDCs appear to be large, cold molecular cores in the earliest stages of star formation. We present a detailed comparison of the extinction at 8 \mum derived from the soon-to-be released MSX Galactic Plane survey images (~18'' resolution) to the 450/850 \mum emission (14'' resolution). The morphologies of the submillimeter emission and mid-infrared extinction are in good agreement. From the comparison, we will determine the dust column density and constrain dust temperature and emissivity. In addition, we present very recent polarimetric imaging of IRDCs at 850 \mum. A relatively high degree of polarization at 850 \mum is seen, suggesting that a well-ordered magnetic field may be present within most IRDCs. In general, the magnetic fields thread the filaments with a more complicated structure near the embedded sources. We will examine the structure of the magnetic field and the star formation properties of IRDCs using the mid-infrared and submillimeter images, submillimeter polarimetry and CO and HCO+ line maps.
The author(s) of this abstract have provided an email address for comments about the abstract: carey@plh.af.mil