2020ApJ...900...40O

Using the Atacama Large Millimeter/submillimeter Array, we have imaged 15 molecular-line emissions and the dust continuum emission around the Class 0 protostellar source IRAS 15398-3359. The outflow structure is mainly traced by the H₂CO (K_a = 0 and 1), CCH, and CS emissions. These lines also trace the disk/envelope structure around the protostar. The H₂CO (K_a = 2 and 3), CH₃OH, and SO emissions are concentrated toward the protostar, while the DCN emission is more extended around the protostar. We have performed principal component analysis (PCA) for these distributions on two different scales, the outflow and the disk/envelope structure. For the latter case, the molecular-line distributions are classified into two groups, according to the contribution of the second principal component, one having a compact distribution around the protostar and the other showing a rather extended distribution over the envelope. Moreover, the second principal component value tends to increase as an increasing quantum number of H₂CO (K_a = 0, 1, 2, and 3), reflecting the excitation condition: the distribution is more compact for higher excitation lines. These results indicate that PCA is effective at extracting the characteristic features of the molecular-line distributions around the protostar in an unbiased way. In addition, we identify four blobs in the outflow structure in the H₂CO lines, some of which can also be seen in the CH₃OH, CS, CCH, and SO emissions. The gas temperature derived from the H₂CO lines ranges from 43-63 K, which suggests shocks due to the local impact of the outflow on clumps of the ambient gas.