Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...466..338c&link_type=abstract
Astrophysical Journal v.466, p.338
Astronomy and Astrophysics
Astronomy
42
Ism: Individual Ngc Number: Ngc 2024, Ism: Kinematics And Dynamics, Ism: Molecules, Stars: Formation, Stars: Circumstellar Matter
Scientific paper
High-resolution images of the NGC 2024 molecular ridge in CS(2-1), CO(1-0), and 3 mm continuum emission have been obtained using the Owens Valley millimeter array. The data are used to determine the temperature and dynamics of the ridge, and to ascertain the evolutionary state of the embedded protostars FIR 2-7. Dust continuum emission is detected from all six FIR sources, and masses of ˜1 Msun are implied assuming a dust temperature of 30 K and a dust opacity index β = 1. The sources are resolved, the majority of the emission probably arising in extended envelopes around the embedded protostars rather than circumstellar disks.
The CS(2-1) follows the ridge closely, but does not always coincide with the FIR sources. The largest discrepancy is for FIR 5, the brightest of the dust continuum sources, where column densities derived from the dust and the CS differ by an order of magnitude. Although either depletion of CS or anomalous grain properties in FIR 5 can explain this result, we also show that if the dust and gas temperature is ≥ 100 K for this compact source, the two column density estimates may be brought into agreement.
The CO(1-0) traces the structure of the compact outflow from FIR 6 and reveals a new outflow from FIR 4. The latter is unipolar, with only a redshifted lobe, but is oriented symmetrically opposite the infrared reflection nebula associated with this source. Assuming the dynamical ages of the outflows from FIR 4-6 are proportional to the age of the underlying protostars, an evolutionary sequence is suggested in the ridge. The formation of so many young protostars at locations separated by ˜0.3 pc may have been triggered by the interaction of the NGC 2024 H II region with the molecular gas.
Carlstrom John E.
Chandler Claire J.
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