Evolution of the Ultraviolet Upturn at $0.3<z<1$: exploring helium rich stellar populations

TL;DR

This study investigates the evolution of the ultraviolet upturn in early-type galaxies across redshifts 0.3 to 1, revealing its decline beyond z=0.6 and supporting models with helium-rich stellar populations formed early in cosmic history.

Contribution

It provides observational evidence for the evolution of the UV upturn up to z=0.6 and supports models involving helium-rich stellar populations formed at high redshift.

Findings

UV upturn detected up to z=0.6

Upturn largely disappears at z=1

Supports helium-rich stellar population models

Abstract

We measure the near-UV (rest-frame $\sim 2400$\AA) to optical color for early-type galaxies in 12 clusters at $0.3 < z < 1.0$. We show that this is a suitable proxy for the more common far-ultraviolet bandpass used to measure the ultraviolet upturn and find that the upturn is detected to $z=0.6$ in these data, in agreement with previous work. We find evidence that the strength of the upturn starts to wane beyond this redshift and largely disappears at $z=1$. Our data is most consistent with models where early-type galaxies contain minority stellar populations with non-cosmological helium abundances, up to around 46\%, formed at $z \geq 3$, resembling multiple stellar population globular clusters in our Galaxy. This suggests that elliptical galaxies and globular clusters share similar chemical evolution and star formation histories. The vast majority of the stellar mass in these galaxies also must have been in place at $z > 3$.