Molecular Distributions of the Protostellar Envelope and the Outflow of IRAS 15398-3359: Principal Component Analysis

TL;DR

This study uses principal component analysis on ALMA observations of IRAS 15398-3359 to classify molecular line distributions around a protostar, revealing excitation conditions and shock features in the outflow and envelope.

Contribution

It introduces PCA as an effective, unbiased method to analyze molecular line distributions in protostellar environments, distinguishing compact and extended structures.

Findings

PCA classifies molecular distributions into compact and extended groups.

Higher excitation lines have more compact distributions.

Shock-related temperature estimates range from 43 to 63 K.

Abstract

We have imaged 15 molecular-line emissions and the dust continuum emission around the Class 0 protostellar source, IRAS 15398-3359, with ALMA. 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 the principal component analysis (PCA) for these distributions on the 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 to extract the characteristic feature 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 to 63 K, which suggests shocks due to the local impact of the outflow on clumps of the ambient gas.