What Does Clustering Tell Us About the Buildup of the Red Sequence?

TL;DR

This study uses galaxy clustering data across various redshifts to investigate how galaxies transition onto the red sequence, revealing insights into satellite quenching times and the role of halo mass in galaxy evolution.

Contribution

It provides new constraints on galaxy quenching mechanisms and challenges models based on critical halo mass, highlighting the evolution of central galaxy reddening over cosmic time.

Findings

Approximately 60% of satellite galaxies are red across all redshifts.

Red satellite galaxies mostly become quenched after accretion into larger halos.

Quenching time scales with redshift as t_Q ~ (1+z)^{-1.5}.

Abstract

We analyze the clustering of red and blue galaxies from four samples spanning a redshift range of 0.4<z<2.0 to test the various scenarios by which galaxies evolve onto the red sequence. The data are taken from the UKIDSS Ultra Deep Survey, DEEP2, and COMBO-17. The use of clustering allows us to determine what fraction of the red sequence is made up of central galaxies and satellite galaxies. At all redshifts, including z=0, the data are consistent with ~60% of satellite galaxies being red or quenched, implying that ~1/3 of the red sequence is comprised of satellite galaxies. More than three-fourths of red satellite galaxies were moved to the red sequence after they were accreted onto a larger halo. The constant fraction of satellite galaxies that are red yields a quenching time for satellite galaxies that depends on redshift in the same way as halo dynamical times; t_Q ~ (1+z)^{-1.5}. In three of the four samples, the data favor a model in which red central galaxies are a random sample of all central galaxies; there is no preferred halo mass scale at which galaxies make the transition from star-forming to red and dead. The large errors on the fourth sample inhibit any conclusions. Theoretical models in which star formation is quenched above a critical halo mass are excluded by these data. A scenario in which mergers create red central galaxies imparts a weaker correlation between halo mass and central galaxy color, but even the merger scenario creates tension with red galaxy clustering at redshifts above 0.5. These results suggest that the mechanism by which central galaxies become red evolves from z=0.5 to z=0.