Spatially Extended Low-ionization Emission Regions (LIERs) at z ∼ 0.9

Abstract

We present spatially resolved emission diagnostics for eight z  ∼ 0.9 galaxies that demonstrate extended low-ionization emission line regions over kpc scales. Eight candidates are selected based on their spatial extent and emission line fluxes from slitless spectroscopic observations with the Hubble Space Telescope /Wide Field Camera 3 G141 and G800L grisms in the well-studied Great Observatories Origins Deep Survey (GOODS) fields. Five of the candidates (62.5%) are matched to X-ray counterparts in the Chandra X-ray Observatory Deep Fields. We modify the traditional Baldwin–Philips–Terlevich (BPT) emission line diagnostic diagram to use [S ii ]/(H α  + [N ii ]) instead of [N ii ]/H α to overcome the blending of [N ii ] and H α  + [N ii ] in the low-resolution slitless grism spectra. We construct emission line ratio maps and place the individual pixels in the modified BPT. The extended low-ionization nuclear emission line regions (LINER)-like emission present in all of our candidates, coupled with X-ray properties consistent with star-forming galaxies and weak [O iii ] λ 5007 Å detections, is inconsistent with purely nuclear sources (LINERs) driven by active galactic nuclei (AGNs). 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 ∼ 0.04), this work provides the first evidence for the non-AGN origin of LINER-like emission out to high redshifts.