Structure of the Dense Molecular Gas in the NGC 1333 IRAS 4 Region

Abstract

The NGC 1333 IRAS 4 region was observed in the HCN and HCO+ J = 1 → 0 lines using a single-dish telescope and in the 2.1 mm continuum and the H2CO J = 212 → 111 line using an interferometer. The single-dish maps show that there are at least two velocity components in emission: one at VLSR = 6.7 km s-1 associated with the IRAS 4 core, and the other at ~8 km s-1 associated with a cloud extended from the SVS 13 complex. In addition, there is a foreground cold layer at ~8 km s-1 that causes absorption over most of the mapped area. The cloud structure suggests that the blue-skewed line profile of IRAS 4A/B may not be a sign of protostellar collapse. Examinations of both single-dish and interferometric maps suggest that the dip previously seen in the interferometric spectra toward IRAS 4A/B may be caused mostly by the large-scale foreground layer and partly by missing short-spacing flux. Absorption by an infalling envelope with an unusual velocity profile cannot be ruled out. The HCO+ map revealed other molecular cores, one associated with SK 1, and the other with SK 10/14. They are probable sites of star formation.