HST/WFC3 Observations of an Off-Nuclear Superbubble in Arp 220

TL;DR

This study uses high-resolution HST/WFC3 imaging to identify a 600 pc bubble near the nucleus of Arp 220, suggesting possible origins from an obscured AGN or intense nuclear star formation.

Contribution

First high-resolution optical and infrared imaging revealing a detailed off-nuclear bubble in Arp 220, linking it to nuclear activity or star formation.

Findings

Detected a 600 pc bubble aligned with outflow axes

Suggests an obscured AGN or intense star formation as origin

Provides insights into nuclear feedback processes in galaxy mergers

Abstract

We present a high spatial resolution optical and infrared study of the circumnuclear region in Arp 220, a late-stage galaxy merger. Narrowband imaging using HST/WFC3 has resolved the previously observed peak in H$\alpha$+[NII] emission into a bubble-shaped feature. This feature measures 1.6" in diameter, or 600 pc, and is only 1" northwest of the western nucleus. The bubble is aligned with the western nucleus and the large-scale outflow axis seen in X-rays. We explore several possibilities for the bubble origin, including a jet or outflow from a hidden active galactic nucleus (AGN), outflows from high levels of star formation within the few hundred pc nuclear gas disk, or an ultraluminous X-ray source. An obscured AGN or high levels of star formation within the inner $\sim$100 pc of the nuclei are favored based on the alignment of the bubble and energetics arguments.