DUST EMISSION FROM STAR-FORMING REGIONS .4. A SURVEY OF IR-STRONG CLOUD CORES

As part of an ongoing program - Dust emission from star forming region s on the cloud core regions of a subset of 51 IR-strong (IRS) and 27 I R-quiet (IRQ) giant molecular clouds (GMCs) defined by CO have been se lected for their associated CS and IRAS FIR emission. The dust emissio n from 13 IRS and 4 IRQ GMCs was mapped with the 15 m SEST telescope a t lambda 1300 mu m. Two of the GMCs of each category were not detected . A total of 12 regions with dust emission were subsequently mapped wi th the IRAM 30 m telescope at the same wavelength but with an angular resolution of similar to 12 ''. Here we present results for six of the dust emission regions. They consist of compact cloud cores embedded i n a more extended dust envelope with hydrogen column densities N-H gre ater than or similar to 10(23) Cm-2. The hydrogen mass associated with the dust emission from compact cores and extendeded envelopes account s for only a few percent of the virial mass derived for the parental G MC. The mass associated with the compact cores on the average accounts for similar to 40% of the mass of cores and envelope. The physical pa rameters of the dust cores are derived and compared with those of W49A , W51A, Orion A and SgrB2 - GMCs well-known for their highly varying h igh-mass star formation activities per unit mass of molecular hydrogen . The cloud cores of our sample are found to span a similar range. The 1R luminosities are estimated from the IRAS survey. The parental IRS GMCs have IR luminosity-to-mass ratios of similar to 3 - 4 L(circle do t)/M(circle dot). IRQ GMCs have ratios of less than or similar to 0.5 L(circle dot)/M(circle dot).