Serendipitous discovery of an optical emission line jet in NGC\,232

TL;DR

This paper reports the discovery of a 3 kpc long optical emission-line jet in NGC 232, detected via integral field spectroscopy, and discusses possible ionization mechanisms, favoring in-situ ionization.

Contribution

It presents the first detailed observation of a long emission-line jet in NGC 232 and analyzes its ionization source, expanding understanding of galaxy jets and their interactions.

Findings

Detected a 3 kpc emission-line jet in NGC 232.

Jet shows extreme line ratios increasing along its length.

Analysis favors in-situ ionization as the main mechanism.

Abstract

We report the detection of a highly collimated linear emission-line structure in the spiral galaxy NGC\,232 through the use of integral field spectroscopy data from the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. This jet--like feature extends radially from the nucleus and is primarily detected in [oiii]$\lambda$5007 without clear evidence of an optical continuum counterpart. The length of the radial structure projected on sky reaches $\sim 3$ kpc, which makes NGC\,232 the second longest emission-line jet reported. The ionized gas presents extreme [Oiii]/H$\beta$ and [Nii]/H$\alpha$ line ratios, increasing along the jet-like structure. We discuss three possible scenarios to explain the observed structure: (i) direct ionization of in-falling material from the intergalactic medium by the AGN; (ii) photo-ionization by an un-detected optical counter-part of the radio jet and (iii) fast shocks ionization due to the lateral expansion of the radio jet across the ISM. Our analysis favors in-situ ionization.