Deciphering the hidden structures of HH 216 and Pillar IV in M16: results from JWST and HST

Abstract

To probe the star formation process, we present an observational investigation of the Pillar IV and an ionized knot HH 216 in the Eagle Nebula (M16). Pillar IV is known to host a Class I protostar that drives a bipolar outflow. The outflow has produced the bow shock, HH 216, which is associated with the red-shifted outflow lobe. The JWST near- and mid-infrared images (resolution ∼0${_{.}^{\prime\prime}}$07–0${_{.}^{\prime\prime}}$7) reveal the protostar as a single, isolated object (below 1000 au). The outer boundary of Pillar IV is depicted with the 3.3 $\mu$m Polycyclic aromatic hydrocarbon (PAH) emission. HH 216 is traced with the 4.05 $\mu$m Brα and the radio continuum emission; however, it is undetected with 4.693 $\mu$m H2 emission. HH 216 seems to be associated with both thermal and non-thermal radio emissions. High-resolution images reveal entangled ionized structures (below 3000 au) of HH 216, which appear to be located towards termination shocks. New knots in 4.693 $\mu$m H2 emission are detected and are mainly found on Pillar IV’s northern side. This particular result supports the previously proposed episodic accretion in the powering source of HH 216. One part of the ionized jet (extent ∼0.16 pc) is discovered on the southern side of the driving source. Using the 12CO(J = 1–0), 12CO(J = 3–2), and 13CO(J = 1–0) emission, observational signposts of cloud-cloud collision (or interacting clouds) towards Pillar IV are investigated. Overall, our results suggest that the interaction of molecular cloud components around 23 and 26 km s−1 might have influenced star formation activity in Pillar IV.