The Structure and Kinematics of Three Class 0 Protostellar Jets from JWST

TL;DR

This study uses JWST NIRSpec and MIRI IFU observations to map shock-ionized [Fe II] and related ionic emission in jets from three protostars—B335, HOPS 153, and HOPS 370—within ~2000 au of their launch. By analyzing knots, wiggles, jet widths, and velocity structure, the authors derive 3D jet velocities, opening angles, and launch inclinations, uncovering non-monotonic widening and notable asymmetries between blue- and red-shifted lobes. A key result is that B335's jet inclination (~57°) differs from the cavity inclination (~83°), suggesting jet precession or time-varying launch conditions; HOPS 153 and HOPS 370 show closer to symmetric launches, with total velocities near 150–185 km s^{-1}. The work highlights the role of disk magnetic fields and warps in shaping inner jet dynamics and provides empirical constraints for jet-launch models in the earliest stages of star formation, with implications for accretion-outflow coupling and angular-momentum transport. $V_{tot}$ and opening angles are quantified with precise JWST-based measurements, and knot proper motions offer a rare migration-based constraint on jet inclination in a nearby source.

Abstract

We present observations of jets within 2000 au of three deeply embedded protostars using 2.9-27 micron observations with JWST. These observations show the morphologies and kinematics of the collimated jets from three protostars, the low-mass Class 0 protostars B335 and HOPS 153, and the intermediate-mass protostar HOPS 370. These jets are traced by shock-ionized fine-structure line emission observed with the JWST NIRSpec and MIRI IFUs. We find that [Fe II] emission traces the full extent of the inner 1000 to 2000 au of the jets, depending on distance to the protostar, while other ions mostly trace isolated shocked knots. The jets show evidence of wiggling motion in the plane of the sky as well as asymmetries between blue and red-shifted lobes. The widths of the jets increase non-monotonically with distance from the central protostar, with opening angles ranging from 2.1 degrees to < 10.1 degrees for the three protostars in the sample. The jets have total velocities ranging from 147 to 184 km/s after correcting for disk inclination. For B335, an 8-month gap between NIRSpec and MIRI MRS observations enabled measurement of the tangential velocity of a shocked knot; in combination with the radial velocity, this shows that the jet has a different inclination than the outflow cavity. We find multiple knots before and during a recent outburst in B335, although the knots were more frequent during the burst. The asymmetries between blue- and red-shifted lobes strongly suggest complex interactions between the circumstellar disks and magnetic fields.

Figures (15)

• Figure 1: Fine-structure emission line maps for B335. All images are displayed with an arcsinh scale. Blue and red arrows indicate the direction of the blue- and red-shifted lobes, respectively. Top: The 4.115, 5.340, 17.936, and 24.519 $\mu$m [Fe II] line maps from left to right, respectively. Bottom: The [Fe II] 25.988, [Ni II] 6.637, [Ne II] 12.814, and [Ar II] 6.985 $\mu$m line maps from left to right, respectively. The 4.115 $\mu$m line is from the NIRSpec data; the rest are from MIRI. The FOV and angular resolution of the MIRI data increases with wavelength; a 500 au scalebar is shown at the bottom left corner, and a beam representing the angular resolution is shown at the bottom right corner. A magenta line marks the size and position angle of the disk, centered at the ALMA position of the protostar. Because the disk of B335 has a radius of $<$16 au, the line appears as a small dot. Shocked knots are labeled along the bottom of the map with arrows pointing to the knots. The larger MIRI FOV covers an additional shocked emission knot to the east that is not covered in the NIRSpec FOV.
• Figure 2: Fine-structure emission line maps for HOPS 153. All images are displayed with an arcsinh scale. Blue and red arrows indicate the direction of the blue- and red-shifted lobes, respectively. Top: The 4.115, 5.340, 17.936, and 24.519 $\mu$m [Fe II] line maps from left to right, respectively. Bottom: The [Fe II] 25.988, [Ni II] 6.637, [Ne II] 12.814, and [Ar II] 6.985 $\mu$m line maps from left to right, respectively. A 1000 au scalebar is shown at the bottom right corner, and a beam representing the angular resolution is shown at the bottom left corner. A magenta line marks the size and position angle of the disk, centered at the ALMA position of the protostar. Shocked knots are labeled along the bottom of the map with arrows pointing to the knots. The larger MIRI FOV covers an additional shocked emission knot that is not covered in the NIRSpec FOV.
• Figure 3: Fine-structure emission line maps for HOPS 370. All images are displayed with an arcsinh scale. Blue and red arrows indicate the direction of the blue- and red-shifted lobes, respectively. Top: The 4.115, 5.340, 17.936, and 24.519 $\mu$m [Fe II] line maps from left to right, respectively. Bottom: The [Fe II] 25.988, [Ni II] 6.637, [Ne II] 12.814, and [Ar II] 6.985 $\mu$m line maps from left to right, respectively. A 1000 au scalebar is shown at the bottom right corner, and a beam representing the angular resolution is shown at the bottom left corner. A magenta line marks the size and position angle of the disk, centered at the ALMA position of the protostar. Two shocked knots are labeled along the right side of the map with arrows pointing to the knots. A magenta star marks the position of the Class II companion to the south.
• Figure 4: The deviation from the central jet axis of the centers of the Gaussian fits to the cross-section of the jets, in each of the [Fe II] lines for the B335, HOPS 153, and HOPS 370 protostars (left to right, respectively). An arbitrary constant, individually for each line, has been added to the offsets (x-axis) to center the data points around 0 au. Blue and red triangles indicate the direction of the blue- and red-shifted lobes, respectively. In this figure and all below, positive y-axis values correspond to the blue-shifted lobe and negative values correspond to the red-shifted lobe. Horizontal magenta dashed lines show the projected distances of shocked knots listed in Table \ref{['tab:knot_pos']}. In the HOPS 370 panel, a magenta star marks the position of the Class II companion.
• Figure 5: The deviation from the central jet axis of the centers of the Gaussian fits to the cross-section of the jets, overlaid on each of the rotated [Fe II] line maps for the B335, HOPS 153, and HOPS 370 protostars (top to bottom, respectively). From left to right in each row are the 4.115, 5.340, 17.936, 24.519, and 25.988 $\mu$m line maps. The assumed central jet axis is shown by a vertical white dashed line.