A recent study has examined the formation of glycolaldehyde and ethanol in the southern outflow of L1157, offering new insights into how these complex organic molecules (iCOMs) are created in interstellar environments. Two primary pathways for the formation of iCOMs have been identified: on the surfaces of dust grains and within the gas phase. Investigating these molecules in regions where protostellar outflows collide with surrounding material can help scientists understand their chemical evolution over time.
This research specifically investigates the potential relationship between glycolaldehyde (CH2OHCHO) and ethanol (C2H5OH), a hypothesis previously suggested in scientific literature. The team aimed to determine whether gas-phase reactions that convert ethanol into glycolaldehyde could account for the observed levels of glycolaldehyde in star-forming regions.
The focus was on the southern outflow of L1157, which contains three shock regions labeled B0, B1, and B2, with ages of approximately 900, 1500, and 2300 years, respectively. The researchers obtained high-resolution maps using the IRAM NOEMA observatory, capturing three lines of glycolaldehyde and one line of ethanol. They calculated the abundances of these molecules in the three shock zones and employed a pseudo time-dependent astrochemical model to simulate various formation scenarios for glycolaldehyde.
According to the model, ethanol is expected to form on dust grains and be released into the gas phase through shocks, where it is progressively transformed into glycolaldehyde through a series of chemical reactions. The study presents the first spatially resolved maps of both glycolaldehyde and ethanol in the L1157 outflow, providing broader insights into solar-like star-forming regions.
Analysis of the abundance ratio of glycolaldehyde to ethanol (/) shows an increase from region B1 to B2, aligning with model predictions. However, the model”s inability to simultaneously explain the observations across all three shock regions suggests potential inaccuracies in its assumptions. These might include uniform excitation temperatures, grain compositions, or gas temperature evolution across the regions. Nevertheless, the findings effectively rule out the idea that all gaseous glycolaldehyde originates solely from grain-surface processes.
Co-authors of this study include Juliette Robuschi, Ana López-Sepulcre, Cecilia Ceccarelli, Layal Chahine, Claudio Codella, and Linda Podio. The research has been accepted for publication in Astronomy & Astrophysics.
