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S.J. Carey (BC), M.P. Egan (AFRL), T.A. Kuchar, D. Mizuno (BC), P.A. Feldman, R.O. Redman (NRC/Canada), S.D. Price (AFRL)
We present a preliminary catalog of infrared-dark clouds (IRDCs) that were identified in the Midcourse Space Experiment (MSX) Galactic Plane Survey images. These objects are clearly visible as absorption features against the diffuse Galactic emission in the 8.3 micron MSX images. IRDCs are cold (T < 15 K), dense (n ~ 106 cm-3) molecular cores with bright embedded submillimeter sources. The embedded sources consist of Class I and Class 0 protostars and pre-protostellar condensations. Approximately 3000 IRDCs have been identified for |b| < 5 degrees. The IRDCs range in size from 1x10-3 to 3x10-2 square degrees. The IRDCs are concentrated along lines of sight containing both star forming regions and bright diffuse mid-infrared emission, such as the Galactic center, molecular ring, and Cygnus X. For a subset of IRDCs, kinematic distances of 1-8 kpc have been determined from millimeter observations of H2CO, CS, C18O and HCO+. IRDC have a wide variety of shapes from globule-like to filamentary. We will present the filling factors, fractal dimension and other morphological identifiers for the IRDCs. In particular, the fractal dimension will be compared to the dimensions of other components of the ISM including GMCs and infrared cirrus. Few IRDCs are associated with previously observed star formation tracers such as far-infrared point sources and maser emission. The catalog will be cross-referenced with published observations of star formation tracers and the properties of previously identified star forming regions will be contrasted with the new objects detected by MSX.
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The author(s) of this abstract have provided an email address for comments about the abstract: Sean.Carey@hanscom.af.mil