The ALMA Protostellar Interferometric Line Survey (PILS): First results
  from an unbiased submillimeter wavelength line survey of the Class 0
  protostellar binary IRAS 16293-2422 with ALMA
  The inner regions of the envelopes surrounding young protostars are
characterised by a complex chemistry, with prebiotic molecules present on the
scales where protoplanetary disks eventually may form. This paper introduces a
systematic survey, "Protostellar Interferometric Line Survey (PILS)" of the
Class 0 protostellar binary IRAS 16293-2422 using the Atacama Large
Millimeter/submillimeter Array (ALMA). The survey covers the full frequency
range from 329 to 363 GHz (0.8 mm) with additional targeted observations at 3.0
and 1.3 mm. More than 10,000 features are detected toward one component in the
protostellar binary. Glycolaldehyde, its isomers, methyl formate and acetic
acid, and its reduced alcohol, ethylene glycol, are clearly detected. For
ethylene glycol both lowest state conformers, aGg' and gGg', are detected, the
latter for the first time in the ISM. The abundance of glycolaldehyde is
comparable to or slightly larger than that of ethylene glycol. In comparison to
the Galactic Center, these two species are over-abundant relative to methanol,
possibly an indication of formation at low temperatures in CO-rich ices. Both
13C and deuterated isotopologues of glycolaldehyde are detected, also for the
first time ever in the ISM. For the deuterated species, a D/H ratio of
approximately 5% is found with no differences between the deuteration in the
different functional groups of glycolaldehyde. Measurements of the 13C-species
lead to a 12C:13C ratio of approximately 30, lower than the typical ISM value.
This low ratio may reflect an enhancement of 13CO in the ice due to either
ion-molecule reactions in the gas before freeze-out or differences in the
temperatures where 12CO and 13CO ices sublimate. The results reinforce the
importance of low-temperature grain surface chemistry for the formation of
prebiotic molecules seen here in the gas after sublimation of the entire ice
mantle.
