Helium Sedimentation and the UV Upturn in Brightest Cluster Galaxies

TL;DR

This paper proposes that helium sedimentation in brightest cluster galaxies enhances their UV emission, especially in massive, low-redshift, relaxed systems, explaining recent GALEX observations of UV excess.

Contribution

It introduces a model linking helium sedimentation to UV upturn in BCGs, providing testable predictions for current observations.

Findings

Helium sedimentation can significantly increase He abundance in BCGs.

UV flux strength correlates with galaxy mass, redshift, and dynamical relaxation.

Model predictions are consistent with recent GALEX+SDSS data.

Abstract

Recent observations with Galaxy Evolution Explorer (GALEX) show strong unexpected UV excess in the spectrum of brightest cluster galaxies (BCGs). It is believed that the excess UV signal is produced by old and evolved core-He burning stars, and the UV flux strength could be greatly enhanced if the progenitor stars have high value of He abundance. In this work, we propose that sedimentation process can greatly enhance the He abundance in BCGs. Our model predicts that the UV flux strength is stronger in more massive, low-redshift, and dynamically relaxed BCGs. These predictions are testable with the current generation of GALEX+SDSS observations.