Discovery of kpc-scale line emission in barred galaxies, not linked to AGN or star formation

TL;DR

This study reveals widespread, low-level LINER-like optical line emission on kiloparsec scales in barred galaxies' bars, unrelated to star formation or AGN activity, likely originating from old stellar populations.

Contribution

It provides detailed spectroscopic evidence of LINER emission in barred galaxy bars, emphasizing its spatial extent and origin from old stars, distinct from star formation or AGN effects.

Findings

Line emission is low-level, smooth, and widespread in barred regions.

Line ratios match LINER characteristics, not star-forming regions.

The emission likely originates from old stellar populations like post-AGB stars.

Abstract

We present an analysis of the optical line emission from nearby barred galaxies, and in particular look at the radial range occupied by the bar. In many cases this region is marked by what we term a 'star formation desert', with a marked deficit of HII regions in optical narrow-band H-alpha imaging. Here we present long-slit spectroscopy revealing that such regions do have line emission, but that it is low-level, spatially smooth and almost ubiquitous. The relative strengths of the H-alpha and the spectrally adjacent [NII] lines in the regions are completely discrepant from those associated with star formation regions, and more closely match expectations for 'LINER' regions. We quantify the total line emission from these extended, kpc-scale regions, and determine the spurious contribution it would make to the determined star formation rate of these galaxies if interpreted as normal H-alpha emission. We concur with previous studies that link this LINER emission to old stellar populations, e.g. post-asymptotic giant branch stars, and propose these strongly-barred early-type spirals as a prime location for further tests of such emission.