Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description

Abstract

We describe a new Large Program in progress on the Gemini North and South\ntelescopes: Gemini Observations of Galaxies in Rich Early Environments\n(GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy\nsystems at $1<z<1.5$, selected to span a factor $>10$ in halo mass. The\nscientific objectives include measuring the role of environment in the\nevolution of low-mass galaxies, and measuring the dynamics and stellar contents\nof their host haloes. The targets are selected from the SpARCS, SPT, COSMOS and\nSXDS surveys, to be the evolutionary counterparts of today's clusters and\ngroups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the\nnod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over\n$\\lambda\\sim 0.6$--$1.05\\mu$m, and this enables a homogeneous and statistically\ncomplete redshift survey of galaxies of all types. The spectroscopic sample\ntargets galaxies with AB magnitudes $z^{\\prime}<24.25$ and [3.6]$\\mu$m$<22.5$,\nand is therefore statistically complete for stellar masses\n$M_\\ast\\gtrsim10^{10.3}M_\\odot$, for all galaxy types and over the entire\nredshift range. Deep, multiwavelength imaging has been acquired over larger\nfields for most systems, spanning $u$ through $K$, in addition to deep IRAC\nimaging at 3.6$\\mu$m. The spectroscopy is $\\sim 50$ per cent complete as of\nsemester 17A, and we anticipate a final sample of $\\sim 500$ new cluster\nmembers. Combined with existing spectroscopy on the brighter galaxies from\nGCLASS, SPT and other sources, GOGREEN will be a large legacy cluster and field\ngalaxy sample at this redshift that spectroscopically covers a wide range in\nstellar mass, halo mass, and clustercentric radius.\n