We are entering an exciting time for cluster cosmology and galaxy evolution studies with current and upcoming surveys such as Euclid, eROSITA and LSST. With the production of these wide-field surveys across a variety of wavelengths and redshift ranges, we are moving into an era where samples of 10^6 galaxy clusters will be available. These large samples enable the reduction of statistical uncertainties, however, the success of future cluster cosmology studies depends on unbiased cluster mass measurements. In the first part of this talk, I will present the results of an extensive blind study, The Galaxy Cluster Mass Reconstruction Project, which was created in order to determine how well we can measure the masses of groups and clusters using the properties of galaxies. In addition to being heavily utilised as mass proxies, cluster galaxies play a central role in studies of mechanisms which may govern the life and death of galaxies in extreme environments. Thanks to extensive studies at low redshift, we know that galaxies in higher-density environments like galaxy clusters have ceased forming stars compared to those in lower-density environments. At z > 1, when the Universe was eight times denser however, the interactions between galaxies and their environment are expected to have been very different compared to that of today. We, therefore, expect the timescales of possible mechanisms driving galaxy evolution to differ. In the second part of this talk I will present preliminary results from the GOGREEN survey: a multi-object spectroscopic campaign of 21 clusters at 1 < z < 1.5 reaching unprecedented stellar masses at this redshift, providing the first look at environmental effects on galaxy evolution at a time when galaxies were growing in a fundamentally different way from today.

Host: Allison Noble