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

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.

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

The exploration of intracluster light (ICL) offers profound insights into the dynamical history and composition of galaxy clusters. The study titled "The Intracluster Light of Abell 3667: Unveiling an Optical Bridge in LSST Precursor Data," is a compelling investigation into the ICL of the Abell 3667, utilizing precursor data analogous to what the upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will achieve. This paper details the creation of a precursor dataset using DECam observations, reaching a depth comparable to LSST’s eighth year, to analyze the intracluster light within Abell 3667 (A3667).

Key Findings and Methodology

The authors have observed an optical bridge of low surface brightness, approximately 400 kpc in extent, bridging the cluster's two brightest galaxies (BCG1 and BCG2). The surface brightness of this bridge is approximately ( \mu \gtrsim 26\text{mag}/arcsec^2 ), indicative of formation through tidal interactions likely triggered by a major merger. The examination reveals that the intracluster light around BCG1 is consistent with gradual stripping of stars from satellite galaxies, whereas BCG2 displays disruptions indicative of a recent merger activity.

The hypothesized scenario suggests a relic structure from a recent first-pass interaction between BCG1 and BCG2, potentially posed by the stripping of stars from BCG2. This aligns with the observed optical and color profiles, showcasing the methodology’s strengths in tracing dynamical events within clusters. The data processing includes implementing the LSST Science Pipelines on DECam observations to manage issues such as background subtraction and stellar contamination, crucial for low surface brightness studies.

Implications

This study's implications are significant for future research using LSST data. The discovery of new features like the optical bridge in A3667 offers a template for what could be achieved with the deeper observational capabilities of LSST. With LSST’s anticipated comprehensive sky coverage using six photometric bands, we may refine our understanding of the formation history and composition of ICL, allowing more precise age and metallicity profiling. Such enriched observational projects can potentially provide clearer insights into the mass distribution and interaction histories of galaxy clusters.

Prospective Developments

While the current findings elucidate the dynamics within A3667, the future of this research lies in correlating optical data with other wavelengths, from X-rays to radio, for a fuller understanding of cluster interactions. Moreover, the refined observational techniques of LSST promise to mitigate current data processing challenges, such as background modeling and star contamination, thus enhancing the fidelity of future ICL studies. Upcoming LSST data will likely revolutionize our observational strategies, fostering more sophisticated modeling and analytical techniques within cluster astrophysics.

Conclusion

The study conducted by Englert, Dell'Antonio, and Montes, sets a vital precursor benchmark for future intracluster light studies, paving the way for groundbreaking discoveries utilizing LSST's capabilities. The discussion on the optical bridge in A3667 exemplifies the dynamic interaction of galaxy clusters and the potential insights ICL can provide into cosmic structure formation and evolution. As we move closer to LSST’s operational phase, research like this propels interest and offers vital preparative strategies to optimize the scientific return from LSST data.