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

TL;DR

Using JWST MIRI/MRS, the study maps the inner 500 au of L1527's bipolar outflow in the mid-infrared, detecting molecular, atomic, and ionized gas that collectively trace a stratified outflow. H2 rotational transitions reveal two gas components, warm and hot, consistent with shock heating and modest UV irradiation within the outflow cavities. Forbidden lines such as [Ne II], [Ne III], and [Ar II] reveal multiple ionization layers and uncover a high-velocity ionized jet embedded within a broader disk wind, with a plane-of-sky orientation (i ≈ 75°) and HV speeds around 100 km s^-1 (deprojected to ~385 km s^-1). The results imply a jet–disk wind structure driven by a weak magnetic field in an early-stage protostar, offering new constraints on jet-launching conditions in Class 0/I systems and demonstrating JWST's capability to probe embedded outflows at high spatial and spectral resolution.

Abstract

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 using JWST MIRI/MRS spectroscopy across 5-28 micron at 0.2-1.0 arcsec resolution. We identify emission lines from molecular and ionized species and analyze their spatial morphology using line integrated intensity maps. We derive gas temperature and column density 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. 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 the presence of 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 co-existence of these components supports a stratified outflow structure and suggest L1527 exhibits unique jet-launching characteristics atypical for its early evolutionary stage.

Figures (14)

• Figure 1: Mid-infrared three-color image of the L1527 bipolar outflow, using JWST MIRI broadband imaging at $5.6\,\mu$m (red), $7.7\,\mu$m (green) and $12.8\,\mu$m (blue). The region spans $1.43\arcmin \times 0.83\arcmin$, corresponding to a physical scale of $12000\,\mathrm{au}\times 7000\,\mathrm{au}$ at a distance of $140\,\mathrm{pc}$. The prominent blue emission at the left edge is not physical, but an artifact of color stretch. The right panel shows a zoomed in view of the 500 au central region with brightness scaled to reveal the bipolar outflow lobes. The position of the forming protostar is marked by a star symbol. Two circular apertures of $\sim0\farcs3$ radius in red and blue are shown corresponding to the area where the MIRI/MRS spectra was extracted. Bottom panel shows the spectra obtained at the aperture positions across the full MIRI/MRS wavelength range ($5-28\,\mu$m). The red colored spectra corresponds to the eastern lobe, whereas the blue spectra corresponds to the western lobe. Flux density of both the spectra are scaled for visual offset.
• Figure 2: Detailed MIRI/MRS spectra extracted at the aperture positions as shown in Fig. \ref{['fig1']}. The four different panels correspond to the spectra from the 4 MIRI channels. Various molecular and ionized emission lines are identified and labeled. Major solid-state absorption features from ices and silicates are indicated in wide colored bands. The red spectra is scaled with an increased offset, as to not overlap with the blue spectra.
• Figure 3: Line integrated intensity (Moment 0) maps of molecular H$_{2}$ 0-0 rotational transitions from S(8) to S(1) covering $5-28\,\mu$m range. The upper state excitation energies for H$_{2}$ are decreasing from S(8) to S(1) transitions (see Table 1). The maps are created after subtracting the local continuum. Brightest regions correspond to strongest H$_{2}$ emission. White contours shown are the $5.6\,\mu$m broadband emission. Position of the central star is shown as a star symbol.
• Figure 4: Line integrated intensity (Moment 0) maps of atomic and ionized emission lines in L1527. The maps cover all the lines detected in the MIRI spectral range and are created after subtracting the local continuum. Brightest white-orange regions correspond to strongest line emission in each of the species. White contours shown are the $5.6\,\mu$m broadband emission. Position of the central protostar is shown as a star symbol.
• Figure 5: Channel map of [Neii] $12.813\,\mu$m continuum subtracted emission in L1527. The maps span radial velocity (V$_{\rm{rest,LSR}}$) interval between -126 km s$^{-1}$ to 106 km s$^{-1}$. Extended emission tracing the outflow on both the lobes is seen. Black contours shown are the $5.6\,\mu$m broadband emission. Position of the central protostar is shown as a star symbol.