Extended Structures of Planetary Nebulae Detected in H$_{2}$ Emission

TL;DR

This study uses deep near-infrared imaging to reveal extended H$_{2}$ emission structures in 11 Galactic planetary nebulae, providing new insights into their morphology and interactions with the interstellar medium.

Contribution

First detection of extended H$_{2}$ structures in several planetary nebulae using deep wide-field imaging, enhancing understanding of nebular morphology and stellar wind interactions.

Findings

H$_{2}$ emission correlates with bipolar nebulae.

Resolved knotty and filamentary structures in H$_{2}$ gas.

Detected a tilted ring structure in Sh1-89.

Abstract

We present narrow-band near-infrared images of a sample of 11 Galactic planetary nebulae (PNe) obtained in the molecular hydrogen (H$_{2}$) 2.122 $\mu$m and Br$\gamma$ 2.166 $\mu$m emission lines and the $K_{\rm c}$ 2.218 $\mu$m continuum. These images were collected with the Wide-field InfraRed Camera (WIRCam) on the 3.6m Canada-France-Hawaii Telescope (CFHT); their unprecedented depth and wide field of view allow us to find extended nebular structures in H$_{2}$ emission in several PNe, some of these being the first detection. The nebular morphologies in H$_{2}$ emission are studied in analogy with the optical images, and indication on stellar wind interactions is discussed. In particular, the complete structure of the highly asymmetric halo in NGC6772 is witnessed in H$_{2}$, which strongly suggests interaction with the interstellar medium. Our sample confirms the general correlation between H$_{2}$ emission and the bipolarity of PNe. The knotty/filamentary fine structures of the H$_{2}$ gas are resolved in the inner regions of several ring-like PNe, also confirming the previous argument that H2 emission mostly comes from knots/clumps embedded within fully ionized material at the equatorial regions. Moreover, the deep H$_{2}$ image of the butterfly-shaped Sh1-89, after removal of field stars, clearly reveals a tilted ring structure at the waist. These high-quality CFHT images justify follow-up detailed morpho-kinematic studies that are desired to deduce the true physical structures of a few PNe in the sample.