The high-redshift evolution of the Red Sequence scatter from joint simulations and HAWK-I Cluster Survey

TL;DR

This study combines simulations and observational data to analyze the evolution of the Red Sequence scatter in galaxy clusters from redshift 0.8 to 1.5, focusing on stellar age and metallicity effects.

Contribution

It provides a comprehensive analysis of the Red Sequence scatter evolution using both hydrodynamical simulations and observational data, highlighting the role of stellar age and metallicity.

Findings

RS scatter increases with cosmic time.

Age spread remains proportional to average age.

Results agree with observational data from HCS.

Abstract

We study the evolution of the Red Sequence (RS) scatter in galaxy clusters and groups simultaneously using predictions from our simulations (cosmological hydrodynamic + semi-analytical) as well as observational data from the HAWK-I Cluster Survey (HCS), a sample of galaxy clusters at redshifts $0.8 < z < 1.5$. We analyze the intrinsic scatter of the RS to investigate whether the stellar age can be its main effective driver, at the same time assessing the role of metallicity variations in shaping the RS building at around epoch $z\sim$1 and beyond. To this purpose we rely on various methods to derive the average age and age spread from the RS colour scatter of the HCS sample, with the aid of population synthesis models. The RS scatter predicted by the models at $z< 0.7$ is found to not depend on the star formation history adopted, whilst at $z>the correlation found between age and rest-frame colour scatters is quite robust, although all age scatter estimations ultimately depend on the definition of RS as well as on the completeness limits adopted. We find that the age spread of RS galaxies predicted by both hydrodynamical simulations and SAM increases with cosmic epoch, while the ratio between the age spread and the average age remains approximately constant. Both trends are in agreement with observational results from both the HCS and other literature samples.