2024A&A...684A.189V

Aims. Interstellar complex organic molecules (iCOMs) are species commonly found in the interstellar medium. They are believed to be crucial seed species for the build-up of chemical complexity in star forming regions as well as our own Solar System. Thus, understanding how their abundances evolve during the star formation process and whether it enriches the emerging planetary system is of paramount importance.
Methods. We use data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disk and envelope system of solar protostars) to study the compact line emission towards the [BHB2007] 11 proto-binary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has previously been detected. More than 45 methyl formate (CH₃OCHO) lines are clearly detected with upper energies in the [123, 366] K range, as well as 8 dimethyl ether transitions (CH₃OCH₃) in the [93, 191] K range, 1 ketene transition (H₂CCO) and 4 formic acid transitions (t-HCOOH). We compute the abundance ratios with respect to CH₃OH for CH₃OCHO, CH₃OCH₃, H₂CCO, t-HCOOH (as well as an upper limit for CH₃CHO) through a radiative transfer analysis. We also report the upper limits on the column densities of nitrogen bearing iCOMs, N(C₂H₅CN) and N(C₂H₃CN).
Results. The emission from the detected iCOMs and their precursors is compact and encompasses both protostars, which are separated by only 0.2″ (∼28 au). The integrated intensities tend to align with the Southern filament, revealed by the high spatial resolution observations of the dust emission at 1.3 mm. A Position-Velocity and 2D analysis are performed on the strongest and uncontaminated CH₃OCH₃ transition and show three different spatial and velocity regions, two of them being close to 11B (Southern filament) and the third one near 11A.
Conclusions. All our observations suggest that the detected methanol, as well as the other iCOMs, are generated by the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and 11B, respectively, making this source one of the few where chemical enrichment of the gas caused by the streaming material is observed.