The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic
  Molecules in Perseus Embedded Protostars
  To date, about two dozen low-mass embedded protostars exhibit rich spectra
with lines of complex organic molecule (COM). These protostars seem to possess
different enrichment in COMs. However, the statistics of COM abundance in
low-mass protostars are limited by the scarcity of observations. This study
introduces the Perseus ALMA Chemistry Survey (PEACHES), which aims at
unbiasedly characterizing the chemistry of COMs toward the embedded (Class 0/I)
protostars in the Perseus molecular cloud. Of 50 embedded protostars surveyed,
58% of them have emission from COMs. A 56%, 32%, and 40% of the protostars have
CH$_3$OH, CH$_3$OCHO, and N-bearing COMs, respectively. The detectability of
COMs depends neither on the averaged continuum brightness temperature, a proxy
of the H$_2$ column density, nor on the bolometric luminosity and the
bolometric temperature. For the protostars with detected COMs, CH$_3$OH has a
tight correlation with CH$_3$CN, spanning more than two orders of magnitude in
column densities normalized by the continuum brightness temperature, suggesting
a chemical relation between CH$_3$OH and CH$_3$CN and a large chemical
diversity in the PEACHES samples at the same time. A similar trend with more
scatter is also found between all identified COMs, hinting at a common
chemistry for the sources with COMs. The correlation between COMs is
insensitive to the protostellar properties, such as the bolometric luminosity
and the bolometric temperature. The abundance of larger COMs (CH$_3$OCHO and
CH$_3$OCH$_3$) relative to that of smaller COMs (CH$_3$OH and CH$_3$CN)
increases with the inferred gas column density, hinting at an efficient
production of complex species in denser envelopes.
