PROJECT-J: the shocking H2 outflow from HH46

TL;DR

PROJECT-J uses JWST NIRSpec-IFU and MIRI-MRS to map H2 emission in the HH46 IRS outflow, uncovering a multi-temperature, shock-driven molecular wind without the temperature or velocity stratification expected from MHD disk-wind models. Rotational and ro-vibrational H2 data, analyzed via bimodal and stratified temperature treatments, reveal warm and hot components embedded in colder gas, with OPR near equilibrium except in some redshifted zones. The data support a two-outflow scenario from a binary HH46 IRS, where the primary drives a collimated atomic jet and the secondary drives a predominantly molecular shell-like outflow, with UV irradiation from shocks shaping H2 excitation. The inferred low-velocity irradiated J-shocks and the estimated mass-loss for source b* (~5×10⁻¹⁰ M⊙ yr⁻¹) imply a markedly lower accretion rate for the secondary (≤~10⁻⁹ M⊙ yr⁻¹) relative to the primary, providing a detailed view of how protostellar jets couple to their environment and regulate early stellar evolution.

Abstract

We analyze the H2 emission observed in the HH46 Class I system as part of PROJECT-J (Protostellar Jets Cradle Tested with JWST), to investigate the origin and excitation of the warm molecular outflow. We used NIRSpec and MIRI spectral maps (1.6-27.9 microns) to trace the structure and physical conditions of the outflow. By fitting the H2 rotational diagrams with a multi-temperature gas model, we derived key physical parameters including temperature, extinction, column densities, and the ortho-to-para ratio. This information is combined with a detailed kinematical analysis and comparison with irradiated shock models. We find no evidence of H2 temperature or velocity stratification from the axis to the edge of the outflow, as would be expected in MHD disk-wind models and as observed in other outflows. Instead, the observations suggest that the H2 emission arises from shock interactions between jet bow shocks and/or wide-angle winds with the ambient medium and cavity walls. NIRSpec emission and velocity maps reveal expanding molecular shells, likely driven by the less luminous source in the binary system. We infer an accretion rate of less than 10^-9 solar masses per year for the secondary source, approximately one order of magnitude lower than that of the primary. The H2 emission is consistent with excitation by low-velocity (approximately 10 km/s) J-type shocks, irradiated by an external UV field that may originate from strong dissociative shocks driven by the atomic jet. Future JWST observations will further constrain the evolution of the expanding shell and the mechanisms driving the outflow.

Figures (22)

• Figure 1: Left: JWST/NIRCam image of HH 46/47, taken from the Mikulski Archive for Space Telescopes (MAST), obtained as part of the DDT program PID4441 (P.I. K. Pontoppidan). The image combines the F200W and F335M filters, which primarily trace the H$_2$ emission, while the F115W filter was used as a jet tracer. Right: Enlargement of the region observed by PROJECT-J. The H$_2$ emission from the red- and blue-shifted lobes is shown in magenta and cyan, respectively. The [Fe$\;$] 5.5 $\mu$m emission tracing the red- and blue-shifted atomic jet is overlaid in red and blue, respectively. The black star marks the source position. The main structures identified in Paper I—such as the atomic jet, molecular cavity, compact knots and bow shocks—are labeled for reference.
• Figure 2: JWST/NIRSpec stacked H$_2$ line intensity map, obtained by combining the $v=1$–0 ro-vibrational transitions from S(1)–S(3) and O(2)–O(7). White contours delineate the brightest regions of the stacked H$_2$ emission (levels from 0.085 to 2.0 MJy sr$^{-1}$), highlighting the arc-shaped morphology of knot A1. Cyan contours trace the [Fe$\;$] 1.81 $\mu$m emission (levels from 0.028 to 0.4 MJy sr$^{-1}$), outlining the collimated jet. The two components of the binary system are marked with stars: the white star denotes the primary source (a$^\star$), and the yellow star marks the secondary (b$^\star$). Blue and yellow lines indicate the newly identified A3b and A1b arcs, associated with the jet from a$^\star$ and the outflow from b$^\star$, respectively.
• Figure 3: MIRI continuum-subtracted H$_2$ line intensity maps of pure rotational transitions. White stars mark the positions of the two sources. Contours of the 0–0 S(7) line at 5.51 $\mu$m (levels from 0.6 to 10.0 MJy sr$^{-1}$) are overlaid on the 0–0 S(1) map at 17.04 $\mu$m. The contours clearly show that the MIRI field of view varies with wavelength, ranging from 6$^{\prime\prime}$$\times$15$^{\prime\prime}$ for the 0–0 S(8) line at 5.05 $\mu$m to 8$^{\prime\prime}$$\times$17$^{\prime\prime}$ for the 0–0 S(1) line at 17.04 $\mu$m.
• Figure 4: Continuum-subtracted map of the H$_2$ 0–0 S(4) line at 8.03 $\mu$m. The NIRSpec field of view is outlined by a black square. Representative regions within the outflow, selected for further analysis, are indicated with white circles. Each circular aperture has a radius of 0.$^{\prime\prime}$4.
• Figure 5: Rotational diagrams with extinction-corrected column densities for regions in the blue-shifted outflow lobe covered by both MIRI and NIRSpec observations. Red and blue symbols correspond to MIRI and NIRSpec data, respectively. Symbols denote transitions from different vibrational levels: $v=0$ (squares), $v=1$ (triangles), $v=2$ (circles), and $v>2$ (stars). Straight lines indicate the two-component linear fits performed for each region.