The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars I. Identifying and Characterizing the Protostellar Content of the OMC2-FIR4 and OMC2-FIR3 Regions

Abstract

We present ALMA (0.87~mm) and VLA (9~mm) observations toward OMC2-FIR4 and OMC2-FIR3 within the Orion integral-shaped filament that are thought to be the nearest regions of intermediate mass star formation. We characterize the continuum sources within these regions on $\sim$40~AU (0\farcs1) scales and associated molecular line emission at a factor of $\sim$30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC2-FIR4, four in OMC2-FIR3, and one additional source just outside OMC2-FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100~AU scales. HOPS-108 is the only protostar in OMC2-FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC2-FIR3 with L~$\sim$~360~\lsun, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate methanol from icy dust grains; overall these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in \twco, but find evidence of interaction between the outflow/jet from HOPS-370 and the OMC2-FIR4 region. The multitude of observational constraints indicate that HOPS-108 is likely a low to intermediate-mass protostar in its main mass accretion phase and it is the most luminous protostar in OMC2-FIR4. The high resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them.