A redshift survey of the nearby galaxy cluster Abell 2107: Global rotation of the cluster and its connection to large-scale structures in the universe

TL;DR

This study investigates the rotational motion of galaxy cluster Abell 2107, revealing strong core rotation linked to large-scale filamentary structures, using extensive spectroscopic redshift data and multiple analysis methods.

Contribution

It provides the first detailed measurement of the cluster's global rotation and its connection to surrounding large-scale structures, based on a large, uniform spectroscopic galaxy sample.

Findings

Strong rotation detected within 20 arcminutes of the cluster center

Rotation amplitude is about 60% of the velocity dispersion

Filamentary structures are connected to the cluster and likely induce rotation

Abstract

We study the rotational motion of the galaxy cluster Abell 2107 at redshift z = 0.04 and its connection to nearby large-scale structures using a large amount of spectroscopic redshift data. By combining 978 new redshifts from the MMT/Hectospec observations with data in the literature, we construct a large sample of 1968 galaxies with measured redshifts at clustercentric radius $R < 60^\prime$. Our sample has high (80%) and spatially uniform completeness at r-band apparent magnitude $m_{r,\textrm{Petro},0}$ < 19.1. We first apply the caustic method to the sample and identify 285 member galaxies of Abell 2107 at $R < 60^\prime$. Then the rotation amplitude and the position angle of rotation axis are measured. We find that the member galaxies show strong global rotation at $R < 20^\prime$ ($v_\textrm{rot}/\sigma_v$ ~0.6) with a significance of > 3.8$\sigma$, which is confirmed by two independent methods. The rotation becomes weaker in outer regions. There are at least five filamentary structures that are connected to the cluster and that consist of known galaxy groups. These structures are smoothly connected to the cluster, which seem to be inducing the global rotation of the cluster through inflow of galaxies.