The asymmetric bipolar [Fe II] jet and H₂ outflow of TMC1A resolved with the JWST NIRSpec Integral Field Unit

¹ Department of Astronomy, University of Virginia, Charlottesville, VA 22903, USA
e-mail: ka8km@virginia.edu
² Institute of Astronomy, Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
³ Chalmers University of Technology, Department of Space, Earth and Environment, 412 96 Gothenburg, Sweden
⁴ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands
⁶ Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark
⁷ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

Received: 26 February 2024
Accepted: 23 April 2024

Abstract

Context. Protostellar outflows exhibit large variations in their structure depending on the observed gas emission. To understand the origin of the observed variations, it is important to analyze the differences in the observed morphology and kinematics of the different tracers. The James Webb Space Telescope (JWST) allows us to study the physical structure of the protostellar outflow through well-known near-infrared shock tracers in a manner unrivaled by other existing ground-based and space-based telescopes at these wavelengths.

Aims. This study analyzes the atomic jet and molecular outflow in the Class I protostar, TMC1A, utilizing spatially resolved [Fe II] and H₂ lines to characterize the morphology and to identify previously undetected spatial features, and compare them to existing observations of TMC1A and its outflows observed at other wavelengths.

Methods. We identified a large number of [Fe II] and H₂ lines within the G140H, G235H, and G395H gratings of the NIRSpec IFU observations. We analyzed their morphology and position-velocity (PV) diagrams. From the observed [Fe II] line ratios, the extinction toward the jet is estimated.

Results. We detected the bipolar Fe jet by revealing, for the first time, the presence of a redshifted atomic jet. Similarly, the red-shifted component of the H₂ slower wide-angle outflow was observed. The [Fe II] and H₂ redhifted emission both exhibit significantly lower flux densities compared to their blueshifted counterparts. Additionally, we report the detection of a collimated high-velocity (~100 km s⁻¹), blueshifted H₂ outflow, suggesting the presence of a molecular jet in addition to the well-known wider angle low-velocity structure. The [Fe II] and H₂ jets show multiple intensity peaks along the jet axis, which may be associated with ongoing or recent outburst events. In addition to the variation in their intensities, the H₂ wide-angle outflow exhibits a ring-like structure. The blueshifted H₂ outflow also shows a left-right brightness asymmetry likely due to interactions with the surrounding ambient medium and molecular outflows. Using the [Fe II] line ratios, the extinction along the atomic jet is estimated to be between A_V = 10–30 on the blueshifted side, with a trend of decreasing extinction with distance from the protostar. A similar A_V is found for the redshifted side, supporting the argument for an intrinsic red-blue outflow lobe asymmetry rather than environmental effects such as extinction. This intrinsic difference revealed by the unprecedented sensitivity of JWST, suggests that younger outflows already exhibit the red-blue side asymmetry more commonly observed toward jets associated with Class II disks.