Evidence of Environmental Quenching at Redshift z ~ 2

TL;DR

This study provides evidence that environmental factors influence galaxy quenching at redshift ~2, with clustering patterns indicating satellite quenching in massive halos and a dependence on galaxy mass and redshift.

Contribution

It presents observational evidence of environmental quenching at z ~ 2, highlighting the mass and redshift dependence of the effect, and estimating the quenching timescale.

Findings

Quiescent galaxies cluster strongly around other quiescent galaxies at z ~ 2.

The quenching probability is higher for lower-mass galaxies (<10^10 Msun).

The environmental quenching timescale is estimated to be 1.5-4 Gyr.

Abstract

We report evidence of environmental quenching among galaxies at redshift ~ 2, namely the probability that a galaxy quenches its star formation activity is enhanced in the regions of space in proximity of other quenched, more massive galaxies. The effect is observed as strong clustering of quiescent galaxies around quiescent galaxies on angular scales \theta < 20 arcsec, corresponding to a proper(comoving) scale of 168 (502) kpc at z = 2. The effect is observed only for quiescent galaxies around other quiescent galaxies; the probability to find star-forming galaxies around quiescent or around star-forming ones is consistent with the clustering strength of galaxies of the same mass and at the same redshift, as observed in dedicated studies of galaxy clustering. The effect is mass dependent in the sense that the quenching probability is stronger for galaxies of smaller mass ($\rm{M_*<10^{10} Msun}$) than for more massive ones, i.e. it follows the opposite trend with mass relative to gravitational galaxy clustering. The spatial scale where the effect is observed suggests these environments are massive halos, in which case the observed effect would likely be satellite quenching. The effect is also redshift dependent in that the clustering strength of quiescent galaxies around other quiescent galaxies at z = 1.6 is ~ 1.7 times larger than that of the galaxies with the same stellar mass at z = 2.6. This redshift dependence allows for a crude estimate of the time scale of environmental quenching of low-mass galaxies, which is in the range 1.5 - 4 Gyr, in broad agreement with other estimates and with our ideas on satellite quenching.