The UV-upturn in brightest cluster galaxies

TL;DR

This study compares the UV-upturn in brightest cluster galaxies with ordinary ellipticals, examining correlations with galaxy and cluster properties, and tests helium-sedimentation models, finding differences but no correlations or support for the sedimentation scenario.

Contribution

It provides a comparative analysis of UV-upturn properties in BCGs versus ellipticals and evaluates the helium-sedimentation hypothesis with observational data.

Findings

Systematic differences in UV-colours between BCGs and ellipticals.

No correlation between UV-upturn and host cluster properties.

Helium-sedimentation model predictions are not supported by observations.

Abstract

This paper is part of a series devoted to the investigation of a large sample of brightest cluster galaxies (BCGs), their properties and the relationships between these and the properties of the host clusters. In this paper, we compare the stellar population properties derived from high signal-to-noise, optical long-slit spectra with the GALEX ultraviolet (UV) colour measurements for 36 nearby BCGs to understand the diversity in the most rapidly evolving feature in old stellar systems, the UV-upturn. We investigate: (1) the possible differences between the UV-upturn of BCGs and those of a control sample of ordinary ellipticals in the same mass range, as well as possible correlations between the UV-upturn and other general properties of the galaxies; (2) possible correlations between the UV-upturn and the properties of the host clusters; (3) recently proposed scenarios where helium-sedimentation in the cluster centre can produce an enhanced UV-upturn. We find systematic differences between the UV-colours of BCGs and ordinary ellipticals, but we do not find correlations between these colours and the properties of the host clusters. Furthermore, the observations do not support the predictions made by the helium-sedimentation model as an enhancer of the UV-upturn.