Spatially Extended Low Ionization Emission Regions (LIERs) at $z\sim0.9$

TL;DR

This study presents spatially resolved emission diagnostics of eight galaxies at z~0.9, revealing extended LINER-like emission regions likely originating from star formation rather than active galactic nuclei, using modified BPT diagnostics.

Contribution

First evidence of non-AGN LINER-like emission at high redshift using spatially resolved diagnostics and a modified BPT diagram.

Findings

Extended LINER-like emission detected in all candidates.

X-ray data suggests star formation, not AGN, as the emission source.

First high-redshift evidence for non-AGN LINER-like emission.

Abstract

We present spatially resolved emission diagnostics for eight $z\sim0.9$ galaxies that demonstrate extended low ionization emission-line regions (LIERs) over kpc scales. Eight candidates are selected based on their spatial extent and emission line fluxes from slitless spectroscopic observations with the HST/WFC3 G141 and G800L grisms in the well-studied GOODS survey fields. Five of the candidates (62.5%) are matched to X-ray counterparts in the \textit{Chandra X-Ray Observatory} Deep Fields. We modify the traditional Baldwin-Philips-Terlevich (BPT) emission line diagnostic diagram to use [SII]/(H$\alpha$+[NII]) instead of [NII]/H$\alpha$ to overcome the blending of [NII] and H$\alpha$+[NII] in the low resolution slitless grism spectra. We construct emission line ratio maps and place the individual pixels in the modified BPT. The extended LINER-like emission present in all of our candidates, coupled with X-Ray properties consistent with star-forming galaxies and weak [OIII]$\lambda$5007\AA\ detections, is inconsistent with purely nuclear sources (LINERs) driven by active galactic nuclei. While recent ground-based integral field unit spectroscopic surveys have revealed significant evidence for diffuse LINER-like emission in galaxies within the local universe $(z\sim0.04)$, this work provides the first evidence for the non-AGN origin of LINER-like emission out to high redshifts.