LARGE AREA MAPPING AT 850 μm. Ⅳ. ANALYSIS OF THE CLUMP DISTRIBUTION IN THE ORION B SOUTH MOLECULAR CLOUD

摘要

We present results from a survey of a 1300 arcmin~2 region of the Orion B South molecular cloud, including NGC 2024, NGC 2023, and the Horsehead Nebula (B33), obtained using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). Submillimeter continuum observations at 450 and 850 μm are discussed. Using an automated algorithm, 57 discrete emission features ("clumps") are identified in the 850 μm map. The physical conditions within these clumps are investigated under the assumption that the objects are in quasi-hydrostatic equilibrium. The best-fit dust temperature for the clumps is found to be T_d = 18 ± 4 K, with the exception of those associated with the few known far-infrared sources residing in NGC 2024. The latter internally heated sources are found to be much warmer. In the region surrounding NGC 2023, the clump dust temperatures agree with clump gas temperatures determined from molecular line excitation measurements of the CO molecule. The bounding pressure on the clumps lies in the range log (k~(-1)P cm~3 K~(-1)) = 6.1 ± 0.3. The cumulative mass distribution is steep at the high-mass end, as is the stellar initial mass function. The distribution flattens significantly at lower masses, with a turnover around 3-10 solar mass.