2019A&A...629A..77G

Context. OMC-2/3 is one of the nearest embedded cluster-forming regions that includes intermediate-mass protostars at early stages of evolution. A previous CO (3-2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases.
Aims. The present work presents a study of the warm gas in the high-velocity emission from several outflows found in CO (3-2) emission by previous observations, determines their physical conditions, and makes a comparison with previous results in low-mass star-forming regions.
Methods. We used the CHAMP+ heterodyne array on the APEX telescope to map the CO (6-5) and CO (7-6) emission in the OMC-2 FIR 6 and OMC-3 MMS 1-6 regions, and to observe ¹³CO (6-5) at selected positions. We analyzed these data together with previous CO (3-2) observations. In addition, we mapped the SiO (5-4) emission in OMC-2 FIR 6.
Results. The CO (6-5) emission was detected in most of the outflow lobes in the mapped regions, while the CO (7-6) was found mostly in the OMC-3 outflows. In the OMC-3 MMS 5 outflow, a previously undetected extremely high-velocity gas was found in CO (6-5). This extremely high-velocity emission arises from the regions close to the central object MMS 5. Radiative transfer models revealed that the high-velocity gas from MMS 5 outflow consists of gas with n_H2=10⁴-10⁵cm^–3 and T>200K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of n_H2>10⁴cm^–3 were found.
Conclusions. The physical conditions and kinematic properties of the young intermediate-mass outflows presented here are similar to those found in outflows from Class 0 low-mass objects. Due to their excitation requirements, mid - J CO lines are good tracers of extremely high-velocity gas in young outflows likely related to jets.