Star formation in the NGC 2024 molecular ridge

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 similar to 1 M. are implied assuming a dust temperature of 30 K and a dust opacity index beta = 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 greater than or similar to 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 similar to 0.3 pc may have been triggered by the interaction of the NGC 2024 H II region with the molecular gas.