OMC-2 FIR 4 under the microscope: Shocks, filaments, and a highly collimated jet at 100 au scales

Abstract

Context. Star-forming molecular clouds are characterised by the ubiquity of intertwined filaments. The filaments have been observed in both high-and low-mass star-forming regions, and they are thought to split into collections of sonic fibres. The locations where filaments converge are termed hubs, and these are associated with the young stellar clusters. However, the observations of filamentary structures within hubs at distances of 75-300 pc require a high angular resolution <2 ′′ (∼ 150-600 au) that limits the number of such studies conducted so far. Aims. The integral shaped filament (ISF) of the Orion A molecular cloud is noted for harbouring several hubs within which no filamentary structures have been observed so far. The goal of our study is to investigate the nature of the filamentary structures within one of these hubs, which is the chemically rich hub OMC-2 FIR 4, and to analyse their emission with high density and shock tracers. Methods. We observed the OMC-2 FIR 4 proto-cluster using Band 6 of the Atacama Large (sub-)Millimetre Array (ALMA) in Cycle 4 with an angular resolution of ∼0.26 ′′ (100 au). We analysed the spatial distribution of dust, the shock tracer SiO, and dense gas tracers (i.e., CH 3 OH, CS, and H 13 CN). We also studied the gas kinematics using SiO and CH 3 OH maps. Results. Our observations for the first time reveal interwoven filamentary structures within OMC-2 FIR 4 that are probed by several tracers. Each filamentary structure is characterised by a distinct velocity as seen from the emission peak of CH 3 OH lines. They also show transonic and supersonic motions. SiO is associated with filaments and also with multiple bow-shock features. The bow-shock features have sizes between ∼500 and 2700 au and are likely produced by the outflow from HOPS-370. Their dynamical ages are <800 yr. In addition, for the first time, we reveal a highly collimated SiO jet (∼1 • ) with a projected length of ∼5200 au from the embedded protostar VLA15. Conclusions. Our study unveiled the previously unresolved filamentary structures as well as the shocks within OMC-2 FIR 4. The kinematics of the filamentary structures might be altered by external and/or internal mechanisms such as the wind from H II regions, the precessing jet from the protostellar source HOPS-370, or the jet from VLA 15. While the complexity of the region, coupled with the limited number of molecular lines in our dataset, makes any clear association with these mechanisms challenging, our study shows that multi-scale observations of these regions are crucial for understanding the accretion processes and flow of material that shape star formation.

Solis

“…These new observations suggest the presence of monopolar outflows in FIR4, which could be more common than previously thought. Chahine et al (2022b) showed a highly collimated (∼ 1 • ) monopolar SiO jet outflow originating from VLA15 in the south-west part of FIR4 (see Fig. 1).…”

“…Recent 100-au scale analysis by Chahine et al (2022b) showed a complex, filamentary structure of the western region of FIR4 at high resolution. In particular, SiO emission unveiled the presence of multiple bow-shock features with sizes between ∼ 500 and 2700 au likely caused by a precessing jet from FIR3 that goes from east to west.…”

“…The brightest emission on the western part of the source, which was also observed in SiO emission by Shimajiri et al (2008), is not the subject of our present analysis. As recently shown by Chahine et al (2022b), this part of FIR4 requires angular and spectral resolution analyses to disentangle the several jets propagating from the members of the protocluster system.…”