James Webb Space Telescope Feed Post

Date: 3/29/2024

JWST study of the DG Tau B disk wind candidate: I -- Overview and Nested H2/CO outflows

RGB NIRCAM images and sketch of the DG Tau B outflow geometry. Left: RGB image of DG Tau B combining three NIRCam exposures in F164N (red) for the [Feii] 1.64µm line + continuum, F212N (green) for the H2 1-0S(1) 2.12µm line + continuum, and F323N (blue) for the 1-0O(5) 3.23µm line + continuum. Right: Schematic representation of the DG Tau B disk and outflows showing their orientation and inclination in space. Abstract: The origin and impact of outflows on proto-planetary disks and planet formation are key open questions. DG Tau B, a Class I protostar with a structured disk and a striking rotating conical CO outflow, recently identified with ALMA as one of the best MHD disk wind candidate, is an ideal target for studying these phenomena. Our aim is to analyse the outflow components intermediate between the fast axial jet and the wider molecular CO outflow to discriminate between the different scenarios at their origin (irradiated/shocked disk wind or swept-up material). Using observations from JWST NIRSpec-IFU, NIRCam and SINFONI/VLT, we investigate the morphology, kinematics and excitation conditions of H2 emission lines of the red-shifted outflow lobe. We find an onion-like structure of the outflows with increasing temperature, velocity and collimation towards the flow axis. The red-shifted H2 emission reveals a narrow conical cavity nested inside the CO outflow and originating from the inner disk regions (< 6 au). The H2 shell exhibits a constant vertical velocity (?22 km/s), twice faster that of the CO flow and an average mass flux of M?(H2) = 3e-11 M?/yr significantly lower than the jet and CO values, suggesting low H2 abundance. The global layered structure of the H2/CO outflows is consistent with an MHD disk wind scenario, with the hot H2 possibly tracing an inner dense photodissociation layer of the wind coming from a launching radius in the disk of 0.2-0.4 au. Further analysis, including MIRI observations will provide additional insights into the H2 excitation mechanisms and the origin of the layered outflows observed in DG Tau B.