Context. Intermediate-mass stars are an important ingredient of our Galaxy and a key to understanding how high- and low-mass
stars form in clusters. One of the closest known young intermediate-mass protoclusters is OMC-2 FIR 4, which is located at
a distance of 420 pc in Orion. This region is one of the few where the complete 500-2000 GHz spectrum has been observed with
the heterodyne spectrometer HIFI on board the Herschel satellite, and unbiased spectral surveys at 0.8, 1, 2, and 3 mm have
been obtained with the JCMT and IRAM 30-m telescopes.
Aims. We aim to disentangle the core multiplicity, to investigate
the morphology of this region in order to study the formation of a low- and intermediate-mass protostar cluster, and to aid
in interpretation of the single-dish line profiles already in our hands.
Methods. We used the IRAM Plateau de Bure
Interferometer to image OMC-2 FIR 4 in the 2-mm continuum emission, as well as in DCO+(2-1), DCN(2-1), C34S(3-2), and several
CH3OH lines. In addition, we analysed observations of the NH3(1, 1) and (2, 2) inversion transitions that used the Very Large
Array of the NRAO. The resulting maps have an angular resolution that allows us to resolve structures of 5″, which is equivalent
to ~2000 AU.
Results. Our observations reveal three spatially resolved sources within OMC-2 FIR 4, of one or several
solar masses each, with hints of further unresolved substructure within them. Two of these sources have elongated shapes and
are associated with dust continuum emission peaks, thus likely containing at least one molecular core each. One of them also
displays radio continuum emission, which may be attributed to a young B3-B4 star that dominates the overall luminosity output
of the region. The third identified source displays a DCO+(2-1) emission peak and weak dust continuum emission. Its higher
abundance of DCO+ relative to the other two regions suggests a lower temperature, hence its possible association with either
a younger low-mass protostar or a starless core. It may alternatively be part of the colder envelope of OMC-2 FIR 4.
Our interferometric observations show the complexity of the intermediate-mass protocluster OMC-2 FIR 4, where multiple cores,
chemical differentiation, and an ionised region all coexist within an area of only 10 000 AU.