Gemini South Observatory
[Gemini Observatory / AURA]
The Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) Survey will take advantage of upgraded detectors, which make Gemini’s GMOS spectrographs the best in the world for studying distant galaxy clusters.

The survey will obtain multi-object spectroscopy of 21 clusters in the redshift range 1<z<1.5, representing the Universe when it was only a third of its present age.  The targets are selected to span a wide range of masses, representing the range of building blocks from which today’s clusters were built.  The sample of over 1000 spectroscopically confirmed members will reach 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.

With up to 15 hours of total integration time on the faintest galaxies, the spectra will allow us to measure the dynamics of different galaxy populations, their stellar populations, and to obtain a robust measurement of the abundance of low-mass, quiescent galaxies.  By combining GOGREEN with our existing data on the lower-redshift descendants of these clusters, we will measure the evolution of satellite galaxy dynamics and stellar populations over the last 9.3-Gyr of cosmic time.  This will provide new leverage to theoretical models, importantly testing them at an epoch where there are currently almost no constraints.