EPISODE III: The Nested Jet/Outflow Morphology of EC 53 Revealed by JWST and ALMA

TL;DR

EC 53 hosts a multi-scale protostellar outflow whose structure and kinematics were mapped with JWST (NIRSpec/MIRI) and ALMA. The data reveal an onion-like arrangement: a compact disk driving a fast, collimated atomic jet nested inside a warm H$_2$ cone, which itself sits within a slower, cold CO outflow along cavity walls. Excitation analyses show distinct hot (≈2500 K) and warm (≈900 K) H$_2 components and non-LTE CO signatures consistent with radiative excitation, supporting magnetohydrodynamic disk-wind predictions while allowing for jet entrainment and wide-angle contributions. The study underscores the power of JWST–ALMA synergy to constrain launching radii, velocities, and temperature stratification across scales in protostellar jets and outflows, with EC 53 providing a detailed case where $PA\approx142.2^{\circ}$, $\theta\approx1.3^{\circ}$, $R_0\lesssim45.9~{ m au}$, and $v_{\rm jet}\sim130~\rm km\,s^{-1}$.

Abstract

We present an extensive study of the structure and kinematics of the jet and outflow of EC 53, a Class I protostar with a quasi-periodic variability, using combined James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations. ALMA continuum observations resolve a compact disk with a radius of $\sim$0.14\arcsec\ (60\,au). Scattered light from the outflow cavity is prominent in the short-wavelength NIRCam and NIRSpec observations, revealing only the southeast nearside lobe. We detected 27 H$_2$ emission lines tracing a narrow, cone-shaped structure within the outflow cavity. A high-velocity ionized jet is detected in several forbidden atomic lines, characterized by a position angle of 142\degree, an opening angle of 1.4\degree, and an estimated geometric launching radius of at most $\sim$40\,au. Mid-infrared CO ro-vibrational emission lines, stronger in the P-branch, show a similar distribution to the H$_2$ emission and are likely to originate from hot gas within the outflow cavity. CO and C$_2$H emission lines detected by ALMA trace slower, colder outflow components and cavity walls. The spatial and kinematic stratification between the hot atomic and molecular components and the colder molecular gas is consistent with predictions from MHD disk wind models, although envelope material entrained by a wide-angle wind or jet may also contribute. Our analysis highlights the powerful synergy between JWST and ALMA in advancing the understanding of protostellar jets and outflows across multiple spatial and physical scales.

Figures (26)

• Figure 1: Near through mid-IR spectra toward EC 53 extracted from two different positions using a 0.4 aperture. The top two panels show the spectrum obtained at the ALMA continuum peak (18:29:51.175, +01:16:40.324), with the NIRSpec spectrum on top and the MIRI spectrum below. The bottom two panels show the same for an outflow position (18:29:51.26, +01:16:38.80), which corresponds to the mid-IR CO emission peak. Detector gaps, major ice absorption features, and emission lines are highlighted in various colors. In both NIRSpec panels, the overlapping portion of the MIRI spectrum is overplotted in red for comparison.
• Figure 2: Reduction process of the H$_2$ 3.235 $\mu$m line emission. (a–d) Integrated intensity maps at each stage of the reduction: (a) after hot pixel removal and flux calibration; (b) quadratic baseline fitting result; (c) after continuum subtraction; and (d) after applying a signal-to-noise (S/N) cut of 3. The image center is shifted southeastward to better display the outflow structure. (e–h) Corresponding peak intensity maps for each stage, respectively. The ALMA continuum center is marked with a red star. (i) Spectrum at the location marked with a red cross in panel (a). Gray vertical dashed lines indicate velocities of $-300$ km s$^{-1}$ and $+300$ km s$^{-1}$, used to define the emission channels. The blue line shows the fitted continuum and Gaussian profile. The red vertical dashed line indicates the Gaussian centroid, which is blueshifted relative to the barycentric velocity of the source ($-8.9$ km s$^{-1}$, thick black dashed line).
• Figure 3: Schematic view of EC 53, highlighting each component analyzed in this work.
• Figure 4: (Top) Continuum of EC 53 observed with JWST NIRSpec and MIRI at different wavelengths. The ALMA continuum is overlaid as red contours. (Bottom) Scattered light around EC 53 imaged by JWST NIRCam in different filters. A white dashed square indicates the area shown in the top panels. The position of the central source is marked with a yellow star. The ALMA continuum peak coincides with the peak positions in all images at wavelengths longer than 2.1 $\mu$m. The colorscale is logarithmic across all panels to accentuate faint details.
• Figure 5: Spectra between 4.55 $\mu$m and 4.90 $\mu$m for the central source (blue) and CO emission peak (red). Both spectra are extracted using a 0.3 aperture. The wavelengths of the $^{12}$CO v=1--0, v=2--1, and $^{13}$CO v=1--0 transitions are marked with black, green, and orange dotted lines, respectively. Two transitions from other species, H$_2$ 0--0 S(9) and [Fe II], are indicated with black dashed lines. The line positions are shown in the rest frame without applying velocity shift corrections.