Interpreting the Clustering of Distant Red Galaxies

TL;DR

This study analyzes the clustering of distant red galaxies at z~2.3, demonstrating that standard halo models can fit the data if nearly all satellite galaxies are DRGs, revealing insights into their formation and quenching timescales.

Contribution

It provides a detailed halo occupation model analysis of DRG clustering, highlighting the high fraction of satellite DRGs and their formation efficiency compared to central galaxies.

Findings

Nearly all satellite galaxies in the luminosity range are DRGs.

The fraction of DRGs among galaxies is approximately 44%.

Star formation quenching timescale for satellites is estimated at 450 Myr.

Abstract

We analyze the angular clustering of z~2.3 distant red galaxies (DRGs) measured by Quadri et al 2008. We find that, with robust estimates of the measurement errors and realistic halo occupation distribution modeling, the measured clustering can be well fit within standard halo occupation models, in contrast to previous results. However, in order to fit the strong break in w(theta) at theta=10 arcsec, nearly all satellite galaxies in the DRG luminosity range are required to be DRGs. Within this luminosity-threshold sample, the fraction of galaxies that are DRGs is ~44%, implying that the formation of DRGs is more efficient for satellite galaxies than for central galaxies. Despite the evolved stellar populations contained within DRGs at z=2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted within 500 Myr. Thus, satellite DRGs must have known they would become satellites well before the time of their accretion. This implies that the formation of DRGs correlates with large-scale environment at fixed halo mass, although the large-scale bias of DRGs can be well fit without such assumptions. Further data are required to resolve this issue. Using the observational estimate that ~30% of DRGs have no ongoing star formation, we infer a timescale for star formation quenching for satellite galaxies of 450 Myr, although the uncertainty on this number is large. However, unless all non-star forming satellite DRGs were quenched before accretion, the quenching timescale is significantly shorter than z~0 estimates. Down to the completeness limit of the Quadri et al sample, we find that the halo masses of central DRGs are ~50% higher than non-DRGs in the same luminosity range, but at the highest halo masses the central galaxies are DRGs only ~2/3 of the time.