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

¹ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁵ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁶ Department of Physics, Maynooth University, Maynooth, Co. Kildare, Ireland
⁷ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁸ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁹ INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 7 July 2025
Accepted: 21 January 2026

Abstract

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 H₂ rotational lines and compared results with shock models.

Results. The observations reveal extended molecular hydrogen emission tracing the bipolar outflow, with the H₂ 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.