Preprocessing Among the Infalling Galaxy Population of EDisCS Clusters
Published:
Abstract
We present results from a low-resolution spectroscopic survey for 21 galaxy clusters at $0.4 < z < 0.8$ selected from the ESO Distant Cluster Survey. We measured spectra using the low-dispersion prism in IMACS on the Magellan Baade telescope and calculate redshifts with an accuracy of $\sigma_z = 0.007$. We find 1763 galaxies that are brighter than $R = 22.9$ in the large-scale cluster environs. We identify the galaxies expected to be accreted by the clusters as they evolve to $z = 0$ using spherical infall models and find that $\sim30\%─70\%$ of the $z = 0$ cluster population lies outside the virial radius at $z\sim0.6$. For analogous clusters at $z = 0$, we calculate that the ratio of galaxies that have fallen into the clusters since $z \sim 0.6$ to those that were already in the core at that redshift is typically between $\sim$0.3 and 1.5. This wide range of ratios is due to intrinsic scatter and is not a function of velocity dispersion, so a variety of infall histories is to be expected for clusters with current velocity dispersions of $300~\mathrm{km~s}^{−1} ≲ σ ≲ 1200~\mathrm{km~s}^{−1}$. Within the infall regions of $z \sim 0.6$ clusters, we find a larger red fraction of galaxies than in the field and greater clustering among red galaxies than blue. We interpret these findings as evidence of “preprocessing,” where galaxies in denser local environments have their star formation rates affected prior to their aggregation into massive clusters, although the possibility of backsplash galaxies complicates the interpretation.
Contribution
The original work was done by Dennis Just and was published in 2015. After publication, a significant error was found in the photometry. Dennis Just left astronomy and I took up the role of revising the work. I redid the photometric redshift analysis using the improved photometry and revisited all of the scientific inferences from those redshifts.