2004ApJ...617.1157C

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_K-1_K+1=2₁₂⟶1₁₁line using an interferometer. The single-dish maps show that there are at least two velocity components in emission: one at V_LSR=6.7 km/s associated with the IRAS 4 core, and the other at ∼8 km/s associated with a cloud extended from the SVS 13 complex. In addition, there is a foreground cold layer at ∼8 km/s 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.