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]/(Hα + [N II]) instead of [N II]/Hα to overcome the blending of [N II] and Hα + [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]λ5007 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.