The Intracluster Light of Abell 3667: Unveiling an Optical Bridge in LSST Precursor Data

TL;DR

This study uses DECam data of Abell 3667 to identify a faint optical bridge connecting two bright galaxies, illustrating intracluster light features that LSST will further explore in the future.

Contribution

First detection of an optical intracluster light bridge in Abell 3667 using precursor LSST data, revealing insights into cluster merger processes.

Findings

Discovered a low surface brightness optical bridge between BCGs.

Bridge's properties suggest formation via a major merger.

Inner regions of BCGs show signs of gradual stripping and recent mergers.

Abstract

Intracluster light, the diffuse glow of stars stripped from galaxies during a cluster's formation, is an established tracer of a cluster's dynamical history. The upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) is set to revolutionize studies of intracluster light by imaging the entire southern sky down to a limiting surface brightness $\mu \gtrsim 30\text{mag}/\text{arcsec}^2$ by year ten. In this letter, we create a precursor LSST dataset (reaching the equivalent of year eight depth) using DECam observations of Abell 3667 and study its intracluster light. We have discovered a low surface brightness ($ \mu \gtrsim 26\text{mag}/\text{arcsec}^2 $) optical bridge extending over $\sim 400\text{ kpc}$ which connects the two brightest galaxies (BCG1 and BCG2) in the cluster; the color and surface brightness of the bridge is consistent with formation via a major merger. The inner regions of BCG1 ($r < 200\text{ kpc}$) and BCG2 ($r < 50\text{ kpc}$) are consistent with formation via gradual stripping of satellite galaxies, but BCG2's outer profile appears disrupted by a recent merger. We hypothesize that the bridge is a relic of a recent first-pass between the two brightest galaxies and is composed of stars being stripped from BCG2. Future studies of intracluster light with LSST will discover new features such as the bridge in local clusters while enabling detailed studies of the stellar populations of these features with its six photometric bands.