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