JOYS: JWST MIRI/MRS spectra of the inner 500 au region of the L1527 IRS bipolar outflow

Context . Outflows and jets are defining characteristics in protostellar evolution, intimately linked to accretion. Understanding their properties and origins is essential for probing the earliest phases of star formation. Aims . This study characterizes the physical and kinematic properties within the innermost 500 au region of the L1527 bipolar outflow, a class 0/I low-mass protostar, as part of the JWST Observations of Young protoStars (JOYS) program. Methods . We obtained spectroscopic observations using the JWST MIRI/MRS instrument across 5-28 μm at 0.2-1.0″ spatial resolution. We identified emission lines from molecular and ionized species and analyzed their spatial morphology using line-integrated intensity maps. We derived gas temperatures and column densities from excitation diagram analysis of H 2 rotational lines and compared results with shock models. Results . The observations reveal extended molecular hydrogen emission tracing the bipolar outflow, with the H 2 gas temperatures distributed into warm (~550 K) and hot (~2500 K) components, likely originating from moderate-velocity J -type shocks and some UV irradiation. We detect forbidden atomic and ionized emission lines of [Ni II ], [Ar II ], [Ne II ], [Ne III ], [S I ], and [Fe II ] showing spatially extended morphology. Double-peaked emission profiles were seen in [Ar II ], [Ne III ], and [Fe II ] in the eastern region, suggesting that the high-velocity component traces a fast, highly ionized jet. A radial velocity map derived from [Ne II ] emission shows the eastern region to be redshifted and the western region blueshifted, contrary to earlier interpretations. Conclusions . The analysis of the MIRI/MRS observations reveals molecular, atomic, and ionized emission lines in this low-mass protostar connected with active outflow signatures. The most striking feature discovered is a poorly collimated high-velocity ionized jet, embedded within a broader, wide-angle molecular outflow likely driven by a disk wind. The coexistence of these components supports a stratified outflow structure and suggests that L1527 exhibits jet-launching characteristics atypical of its early evolutionary stage.