| Abstract: | We present a first look at the SCUBA-2 observations of three sub-regions of
the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from
the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in
L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850
micron map, and present their basic properties, including their peak fluxes,
total fluxes, and sizes, and an estimate of the corresponding 450 micron peak
fluxes and total fluxes, using the FellWalker source extraction algorithm.
Assuming a constant temperature of 20 K, the starless dense cores have a mass
function similar to that found in previous dense core analyses, with a
Salpeter-like slope at the high-mass end. The majority of cores appear stable
to gravitational collapse when considering only thermal pressure; indeed, most
of the cores which have masses above the thermal Jeans mass are already
associated with at least one protostar. At higher cloud column densities, above
1-2 x 10^23 cm^-2, most of the mass is found within dense cores, while at lower
cloud column densities, below 1 x 10^23 cm^-2, this fraction drops to 10% or
lower. Overall, the fraction of dense cores associated with a protostar is
quite small (<8%), but becomes larger for the densest and most centrally
concentrated cores. NGC 2023 / 2024 and NGC 2068/2071 appear to be on the path
to forming a significant number of stars in the future, while L1622 has little
additional mass in dense cores to form many new stars. |
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