Evolution of the UV upturn in cluster galaxies: Abell 1689
Sadman S. Ali (1), Malcolm N. Bremer (1), Steven Phillipps (1),, Roberto De Propris (2) ((1) H. H. Wills Physics Laboratory, University of, Bristol, UK, (2) FINCA, University of Turku, Finland)
TL;DR
This study measures the UV upturn in cluster galaxies at z=0.18 and finds it unchanged over 2.2 billion years, supporting models with Helium-enriched hot horizontal branch stars as the source.
Contribution
It provides observational evidence that the UV upturn has not declined over 2.2 Gyrs, supporting Helium-enrichment models for the UV flux in cluster galaxies.
Findings
UV upturn strength unchanged over 2.2 Gyrs
Supports Helium-enriched hot horizontal branch star models
Implications for high formation redshifts and Helium abundance
Abstract
We have measured the strength of the UV upturn for red sequence galaxies in the Abell~1689 cluster at , reaching to or below the level and therefore probing the general evolution of the upturn phenomenon. We find that the range of UV upturn strengths in the population as a whole has not declined over the past 2.2 Gyrs. This is consistent with a model where hot horizontal branch stars, produced by a Helium-enriched population, provide the required UV flux. Based on local counterparts, this interpretation of the result implies Helium abundances of at least 1.5 times the primordial value for this HB population, along with high formation and assembly redshifts for the galaxies and at least a subset of their stellar populations.
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