Seeds of Life in Space (SOLIS). X. Interstellar Complex Organic
  Molecules in the NGC 1333 IRAS 4A outflows
  Aims: A unique environment to study how interstellar Complex Organic
Molecules (iCOMs) can be formed is the shocked gas along low-mass protostellar
outflows, as the dust mantles composition is sputtered into the gas phase. The
chemical richness in these environments has been so far studied only in the
L1157 blue shifted outflow. Methods: To understand if the L1157-B1 case is
unique, we imaged the NGC 1333 IRAS 4A outflows using the NOEMA (NOrthern
Extended Millimeter Array) interferometer as part of the IRAM SOLIS (Seeds Of
Life in Space) Large Program and compared the observations with the GRAINOBLE+
gas phase astrochemical model. Results: Several iCOMs were detected in the IRAS
4A outflows: methanol (CH$_3$OH), acetaldehyde (CH$_3$CHO), formamide
(NH$_2$CHO) and dimethyl ether (CH$_3$OCH$_3$), all sampling upper excitation
energy up to $\sim$30 K. We found a significant chemical differentiation
between the IRAS 4A1 outflow, showing a richer molecular content, and the IRAS
4A2 one. The CH$_3$OH/CH$_3$CHO abundance ratio is lower by a factor $\sim$4 in
the former; furthermore the ratio in both outflows is lower by a factor
$\sim$10 with respect to hot corinos values. Conclusions: After L1157-B1, IRAS
4A outflow is now the second outflow to show an evident chemical complexity.
Given that CH$_3$OH is a grain surface species, GRAINOBLE+ reproduced our
observations assuming acetaldehyde formation in gas phase by the reaction of
ethyl radical (CH$_3$CH$_2$) with atomic oxygen. Moreover, the chemical
differentiation between the two outflows suggests that the IRAS 4A1 outflow is
likely younger than the IRAS 4A2 one. Further investigation is needed to
constrain the age of the outflow and observations of even younger shocks are
necessary and future spectroscopic studies on CH$_3$CH$_2$ are needed to be
able to observe this species and provide strong constraints on the CH$_3$CHO
formation.
