Revealing the star formation history of a mature galaxy cluster at z=2

At z=1.98, XLSSC 122 is a massive and mature galaxy cluster with 37 spectroscopically confirmed members. We employ12 band PSF-matched photometry and BAGPIPES SED modelling to investigate the star formation histories, stellar mass, dust and metal content of the 37 confirmed members. XLSSC 122 therefore provides a unique opportunity to explore massive galaxy evolution in dense environments at early times. The galaxy star formation history results can be placed in the context of the cluster accretion history, using cosmological simulations such as the MultiDark Planck 2 simulation. We demonstrate that red-sequence galaxies display a range of ages, from greater than 2 Gyrs for the BCG to 0.5 Gyr for the less massive satellite galaxies. Comparisons with simulated galaxy clusters show that the oldest cluster members formed when XLSSC 122 had assembled 10 to 30% of its z=2 mass, a result that provides an important new view of the mass-scale associated with both the onset and cessation of star formation in this cluster.AT is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship-Doctoral Program. JPW acknowledges support from the NSERC Discovery Grant program