Investigating Protostellar Accretion (IPA) is a Cycle 1 JWST program using
the NIRSpec+MIRI IFUs to obtain 2.9--28 μm spectral cubes of five young
protostars with luminosities of 0.2 to 10,000 L⊙​ in their primary
accretion phase. This paper introduces the NIRSpec 2.9--5.3 μm data of the
inner 840-9000 au with spatial resolutions from 28-300 au. The spectra show
rising continuum emission, deep ice absorption, emission from H2​, H~I, and
[Fe~II], and the CO fundamental series in emission and absorption. Maps of the
continuum emission show scattered light cavities for all five protostars. In
the cavities, collimated jets are detected in [Fe~II] for the four <320~L⊙​ protostars, two of which are additionally traced in
Br-α. Knots of [Fe~II] emission are detected toward the most luminous
protostar, and knots of [FeII] emission with dynamical times of <30~yrs are
found in the jets of the others. While only one jet is traced in H2​, knots
of H2​ and CO are detected in the jets of four protostars. H2​ is seen
extending through the cavities showing they are filled by warm molecular gas.
Bright H2​ emission is seen along the walls of a single cavity, while in
three cavities, narrow shells of H2​ emission are found, one of which has an
[Fe~II] knot at its apex. These data show cavities containing collimated jets
traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle
wind and/or gas accelerated by bow shocks in the jets.Comment: 30 pages, 11 figure