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Preprocessing among the Infalling Galaxy Population of EDisCS Clusters


Matthew Kirby

Dennis W. Just

Dennis Zaritsky

Gregory Rudnick

Tyler Desjardins

Richard Cool

John Moustakas

Douglas Clowe

Gabriella De Lucia

Vandana Desai

Rose Finn

Claire Halliday

Pascale Jablonka

Justin Mann

Bianca Poggianti

Fu-Yan Bian

Kelley Liebst


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 σ 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 ~30%–70% of the z = 0 cluster population lies outside the virial radius at z ~ 0.6. For analogous clusters at z = 0, we calculate that the ratio of galaxies that have fallen into the clusters since z ~ 0.6 to those that were already in the core at that redshift is typically between ~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 km s−1 lesssim σ lesssim 1200 km s−1. Within the infall regions of z ~ 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.


Kirby, M., Just, D. W., Zaritsky, D., Rudnick, G., Desjardins, T., Cool, R., …Liebst, K. (2019). Preprocessing among the Infalling Galaxy Population of EDisCS Clusters. Astrophysical Journal, 885(1), Article 6.

Journal Article Type Article
Acceptance Date Sep 12, 2019
Online Publication Date Oct 24, 2019
Publication Date Nov 1, 2019
Deposit Date Oct 31, 2019
Publicly Available Date Oct 31, 2019
Journal Astrophysical Journal
Print ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 885
Issue 1
Article Number 6
Keywords Space and Planetary Science; Astronomy and Astrophysics
Public URL
Publisher URL


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