Evidence for anisotropic quenching in massive galaxy clusters at $z\approx0.5$

TL;DR

This study provides evidence that satellite galaxy quenching in massive clusters at z~0.5 depends on their angular position relative to the central galaxy's major axis, suggesting anisotropic environmental effects.

Contribution

It extends the observation of anisotropic quenching from local groups to clusters at higher redshift, indicating a persistent angular dependence over 4 billion years.

Findings

Galaxies near the major axis are more quenched than those near the minor axis.

Star-forming galaxies tend to avoid regions within 45 degrees of the major axis.

The quenching pattern may be driven by AGN outflows along the minor axis.

Abstract

A recent observational result finds that the quenching of satellites in groups at $z=0.08$ has an angular dependence relative to the semi-major axis of the central galaxy. This observation is described as `anisotropic quenching' or `angular conformity'. In this paper I study the variation in the colour of a mass limited sample of satellite galaxies relative to their angle from the major axis of the Brightest Cluster Galaxy in the CLASH clusters up to $z\sim0.5$, 4 Gyr further in lookback time. The same result is found: galaxies close to the major axis are more quenched than those along the minor axis. I also find that the star-forming galaxies tend to avoid a region +/-45 degrees from the major axis. This quenching signal is thought to be driven by AGN outflows along the minor axis, reducing the density of the intergalactic medium and thus the strength of ram pressure. Here I will discuss potential alternative mechanisms. Finally, I note that the advent of the Legacy Survey of Space and Time (LSST) and Euclid surveys will allow for a more detailed study of this phenomenon and its evolution.