The Diverse Nature of Optical Emission Lines in Brightest Cluster Galaxies: IFU Observations of the Central Kiloparsecs

TL;DR

This study uses integral field spectroscopy to analyze the diverse optical emission line properties in nine brightest cluster galaxies, revealing varied ionization mechanisms and challenging previous assumptions about cooling flow correlations.

Contribution

It provides the first detailed IFU-based analysis showing the diversity of emission line morphologies and ionization sources in BCGs, regardless of cooling flow status.

Findings

Diverse emission morphologies observed, including filamentary, extended, and concentrated emission.

Multiple ionization mechanisms identified, including AGN activity and star formation.

No clear link between cooling flow presence and emission line properties.

Abstract

We present integral field spectroscopy of the nebular line emission in a sample of 9 brightest cluster galaxies (BCGs). The sample was chosen to probe both cooling flow and non-cooling flow clusters, as well as a range of cluster X-ray luminosities. The line emission morphology and velocity gradients suggest a great diversity in the properties of the line emitting gas. While some BGCs show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and MKW3s), others have extended emission (Abell 1204, Abell 2199), while still others have centrally concentrated emission (Abell 2052). We examine diagnostic line ratios to determine the dominant ionization mechanisms in each galaxy. Most of the galaxies show regions with AGN-like spectra, however for two BCGs, Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which can be described by the emission from young stellar populations. The diversity of emission line properties in our sample of BCGs suggests that the emission mechanism is not universal, with different ionization processes dominating different systems. Given this diversity, there is no evidence for a clear distinction of the emission line properties between cooling flow and non-cooling flow BCGs. It is not always cooling flow BCGs which show emission (or young stellar populations), and non-cooling flow BCGs which do not.