A search for ionised gas outflows in an Hα imaging atlas of nearby LINERs^⋆

Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: lhermosa@iaa.es

Received: 9 November 2021
Accepted: 13 January 2022

Abstract

Context. Outflows play a major role in the evolution of galaxies. However, we do not yet have a complete picture of their properties (extension, geometry, orientation, and clumpiness). For low-luminosity active galactic nuclei (AGNs), in particular low-ionisation nuclear emission line regions (LINERs), the rate of outflows and their properties are largely unknown.

Aims. The main goal of this work is to create the largest up-to-date atlas of ionised gas outflow candidates in a sample of 70 nearby LINERs. We aim to use narrowband imaging data to analyse the morphological properties of the ionised gas nuclear emission of these galaxies and to identify signatures of extended emission with distinctive outflow morphologies.

Methods. We obtained new imaging data from Alhambra Faint Object Spectrograph and Camera (ALFOSC)/Nordic Optical Telescope (NOT) for a total of 32 LINERs, and complemented it with Hubble Space Telescope archival data (HST) for six objects. We extracted the Hα emission of the galaxies and used it to morphologically classify the circumnuclear emission. We combined our results with those from the literature for additional 32 targets. We additionally obtained soft X-ray data from Chandra archive to compare this emission with the ionised gas.

Results. The distribution of the ionised gas in these LINER indicates that ∼32% show Bubble emission, ∼28% show Core-halo unresolved emission, and ∼21% of the sample have a Disky distribution. Dust lanes prevent any detailed classification for ∼11% of the sample, which we call Dusty. The soft X-ray emission is in most cases (∼60%) co-spatial with the ionised gas. If we account for the kinematical information which is available for a total of 60 galaxies, we end up with a total of 48% of the LINERs with detected outflows or inflows in the emission lines (50% considering only kinematical information based on Integral Field Spectroscopic data).

Conclusions. Our results suggest that the incidence of outflows in LINERs may vary from 41% to 56%, based on both the Hα morphology and the kinematical information from the literature. The ionised gas seems to be correlated with the soft X-ray emission, so that they may have a common origin. We discuss the use of Hα imaging for the pre-selection of candidates likely hosting ionised gas outflows.