Intrinsic alignments in redMaPPer clusters -- I. Central galaxy alignments and angular segregation of satellites

TL;DR

This study investigates the factors influencing central galaxy alignments and satellite angular segregation in galaxy clusters, revealing correlations with cluster elongation, richness, and galaxy properties, based on SDSS data.

Contribution

It identifies key galaxy and cluster properties that predict central galaxy alignments and satellite segregation, advancing understanding of galaxy cluster dynamics.

Findings

Central galaxies align more in elongated, rich clusters.

Redder, larger, and more luminous centrals show stronger alignments.

Redder, more luminous, closer, and rounder satellites exhibit greater angular segregation.

Abstract

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94817 members within 0.1<z<0.35, based on the redMaPPer cluster catalog constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes and the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centering probability, and redder color. Satellites with redder color, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation toward their central galaxy major axes. Finally, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.