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

TL;DR

This paper uses JWST MIRI/MRS spectroscopy to analyze the physical and kinematic properties of the innermost 500 au region of the L1527 bipolar outflow, revealing a stratified outflow structure with a high-velocity ionized jet within a molecular outflow.

Contribution

First detailed JWST MIRI/MRS spectral analysis of L1527's inner outflow, identifying multiple emission lines and revealing a complex stratified outflow structure with a jet and molecular wind.

Findings

Detected extended molecular hydrogen emission with warm and hot components.

Identified a poorly collimated high-velocity ionized jet within a broader molecular outflow.

Revealed a stratified outflow structure with a jet-launching mechanism.

Abstract

This study characterized the physical and kinematic properties within the innermost 500 au region of the L1527 bipolar outflow, a class 0/I low-mass protostar using JWST MIRI/MRS spectroscopy across 5-28 micron at 0.2-1.0 arcsec 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 through excitation diagram analysis of H2 rotational lines and compared results with shock models. 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. 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 the presence of 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 unique jet-launching characteristics atypical of its early evolutionary stage.