Warm gas in protostellar outflows. II. EHV jet and outflows from OMC-2/3

TL;DR

This study investigates warm gas in protostellar outflows within OMC-2/3, revealing high-velocity gas properties similar to low-mass star formation regions and emphasizing the role of mid-J CO lines as tracers.

Contribution

It provides new observations of CO (6--5) and (7--6) emissions in OMC-2/3, identifying extremely high velocity gas near MMS 5 and comparing physical conditions with low-mass protostars.

Findings

High-velocity gas near MMS 5 has densities of 10^4-10^5 cm^-3 and temperatures over 200 K.

Physical conditions of intermediate-mass outflows resemble those of Class 0 low-mass protostars.

Mid-J CO lines effectively trace extremely high velocity gas in young outflows.

Abstract

OMC-2/3 is one of the nearest embedded cluster-forming region 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. The present work aims to study the warm gas in the high-velocity emission from several outflows found in CO (3--2) emission by previous observations, determine their physical conditions, and make comparison with previous results in low-mass star-forming regions. We use 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 $^{13}$CO (6--5) at selected positions. We analyze these data together with previous CO (3--2) observations. In addition, we mapped the SiO (5--4) emission in OMC-2 FIR 6. 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 from 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_{\rm H_2}=$10$^4$--10$^{5}$ cm$^{-3}$ and $T>$ 200 K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of $n_{\rm H_2}>$10$^{4}$ cm$^{-3}$ were found. 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.