Spectral properties of Transition Galaxies from the GOGREEN Survey of Distant Clusters

Using data taken from GOGREEN (Gemini Observations of Galaxies in Rich Early ENvironments), I examined the one-dimensional spectra of galaxies that were considered in transition. GOGREEN is an international survey of galaxies in dense environments within redshift range 0.8 < z < 1.5 using multiwavelength photometry and Gemini spectroscopy. Galaxy evolution in clusters is important to examine because it shows how galaxies in a cluster, that are under hydrodynamic effects of the intrascluster medium that affect the interstellar medium within galaxies, differ in evolution to field galaxies. One way to study the difference in evolutionary paths of field vs. cluster galaxies is to look at their star-formation rates and star formation histories. Galaxies can be actively star-forming, passive (quenching), or in transition, so we have to know what causes a galaxy to quench and we therefore examine galaxies in transition between star-forming and passive. Galaxies quench when they lack the dust and gas to form more stars and leave the active star-forming class. The spectra of galaxies can tell us if a galaxy is quenching or not by looking at emission and absorption lines of atoms that are indicators of ongoing or recent star formation, such as the tracer [OII] equivalent width of the first two lines, H-Delta and the D4000 break. I determined which galaxies were in transition by defining a region in the U-V vs. V-J (UVJ) color-space that is between the star-forming and passive regions. Using the tracers discussed, I examined their properties for the three different classes of galaxies: passive, in transition and active star-forming. I will comment on the ways in which these different types of galaxies differ in their spectral properties and how the strength of their spectral lines show if the galaxy is quenching and why.