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