Herschel/PACS far-IR spectral imaging of a jet from an intermediate mass
  protostar in the OMC-2 region
  We present the first detection of a jet in the far-IR [O I] lines from an
intermediate mass protostar. We have carried out a Herschel/PACS spectral
mapping study in the [O I] lines of OMC-2 FIR 3 and FIR 4, two of the most
luminous protostars in Orion outside of the Orion Nebula. The spatial
morphology of the fine structure line emission reveals the presence of an
extended photodissociation region (PDR) and a narrow, but intense jet
connecting the two protostars. The jet seen in [O I] emission is spatially
aligned with the Spitzer/IRAC 4.5 micron jet and the CO (6-5) molecular outflow
centered on FIR 3. The mass loss rate derived from the total [O I] 63 micron
line luminosity of the jet is 7.7 x 10^-6 M_sun/yr, more than an order of
magnitude higher than that measured for typical low mass class 0 protostars.
The implied accretion luminosity is significantly higher than the observed
bolometric luminosity of FIR 4, indicating that the [O I] jet is unlikely to be
associated with FIR 4. We argue that the peak line emission seen toward FIR 4
originates in the terminal shock produced by the jet driven by FIR 3. The
higher mass-loss rate that we find for FIR 3 is consistent with the idea that
intermediate mass protostars drive more powerful jets than their low-mass
counterparts. Our results also call into question the nature of FIR 4.
