  Glycolaldehyde (HCOCH2OH) is the simplest sugar and an important intermediate
in the path toward forming more complex biologically relevant molecules. In
this paper we present the first detection of 13 transitions of glycolaldehyde
around a solar-type young star, through Atacama Large Millimeter Array (ALMA)
observations of the Class 0 protostellar binary IRAS 16293-2422 at 220 GHz (6
transitions) and 690 GHz (7 transitions). The glycolaldehyde lines have their
origin in warm (200-300 K) gas close to the individual components of the
binary. Glycolaldehyde co-exists with its isomer, methyl formate (HCOOCH3),
which is a factor 10-15 more abundant toward the two sources. The data also
show a tentative detection of ethylene glycol, the reduced alcohol of
glycolaldehyde. In the 690 GHz data, the seven transitions predicted to have
the highest optical depths based on modeling of the 220 GHz lines all show
red-shifted absorption profiles toward one of the components in the binary
(IRAS16293B) indicative of infall and emission at the systemic velocity offset
from this by about 0.2" (25 AU). We discuss the constraints on the chemical
formation of glycolaldehyde and other organic species - in particular, in the
context of laboratory experiments of photochemistry of methanol-containing
ices. The relative abundances appear to be consistent with UV photochemistry of
a CH3OH-CO mixed ice that has undergone mild heating. The order of magnitude
increase in line density in these early ALMA data illustrate its huge potential
to reveal the full chemical complexity associated with the formation of solar
system analogs.
