Dusty cavity and molecular shock driven by IRS7B in the CoronaAustralis Cluster

The process that led to the formation of our Solar System and the origin of the observed prebiotic compounds are among the most exciting open questions in modern astrochemistry. The first results of the Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST; PI: S. Yamamoto; Codella et al. 2021) ALMA Large Program suggest that the chemical composition and fate of future planetary systems strongly depend on the history of the parental protostellar envelope.
I will present new FAUST high-angular resolution (50 au) observations of interstellar Complex Organic Molecules (iCOMs; i.e. organic molecules with at least 6 atoms; Ceccarelli et al. 2017) and dust continuum emission towards the Corona Australis (CrA) star cluster (see Figure 1). The CH₃OH emission reveals an arc-structure at ~1800 au from the protostellar system IRS7B along the direction perpendicular to the disk major axis (see Figure 2a). The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B (see Figure 1). The region inside the cone is probed by H ₂ CO (see Figure 2d), while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer (see Figure 2e). Taking into account the association with a previously discovered radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process.
We derive for each cavity wall an average H₂ column density of ∼ 7×10²¹ cm^-2 , a mass of ∼ 9×10^-3 M_⊙ , and a lower limit on the dust spectral index of 1.4.
These observations provide the first evidence of the shock and the conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar-System analogues.

Figure 1:  Left: SCUBA map at 450µm; Central: ALMA map of 1.3mm continuum emission from Sabatini et al (2024). Right: Zoom around IRS7B. Our ALMA continuum map reveals for the first time the dust grains in the walls of the cavity (cyan dashed lines) opened by the jet driven by IRS7B (cyan solid line).

Figure 2: Moment 0 of (a) CH₃OH-E (4_2,3 -3_1,2), (b) CH₃OH-A (5_1,4-4_1,3), (d) p-H₂CO (3_0,3-2_0,2), (e) SiO (5-4) lines, around the molecular arc (integrated from 0 to +12 km s⁻¹). Cyan lines and arrows follow Figure 1. The white contours mark the 5σ emission. Small circles indicate the positions of the brightest spots in CH₃OH (4_2,3-3_1,2), SiO (5-4), and p-H₂CO (3_0,3-2_0,2), i.e. labelled “A”, “B” and “C”, respectively. Red cross indicates the position of SMM 1A (Figure 1). The green semicircle shows the ALMA Band 6 FoV, while the grey background delimits the region inside each ALMA pointing.