The Vera Rubin Observatory Legacy Survey of Space and Time and the Low Surface Brightness Universe

Abstract: The 8.4m Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will start a ten-year survey of the southern hemisphere sky in 2023. LSST will revolutionise low surface brightness astronomy. It will transform our understanding of galaxy evolution, through the study of low surface brightness features around galaxies (faint shells, tidal tails, halos and stellar streams), discovery of low surface brightness galaxies and the first set of statistical measurements of the intracluster light over a significant range of cluster masses and redshifts.

• The paper demonstrates that LSST's survey will capture extremely faint galaxy features, overcoming traditional surface brightness limits.
• It details innovative imaging and data reduction methods that push detection depths beyond 32 mag arcsec⁻², enabling new observations of tidal streams and ultra-faint dwarfs.
• The study offers transformative insights into intracluster light and galaxy merger histories, refining theoretical models of galaxy evolution.

The Vera Rubin Observatory Legacy Survey of Space and Time and the Low Surface Brightness Universe

Introduction

The Vera Rubin Observatory Legacy Survey of Space and Time (LSST) represents a pivotal advancement in low surface brightness (LSB) astronomy. This ten-year survey, starting in 2023, aims to transform our understanding of galaxy evolution by probing faint features around galaxies, discovering LSB galaxies, and measuring intracluster light (ICL) across a wide range of cluster masses and redshifts. The study of LSB phenomena is crucial as these features encode interactions and hierarchical structure formation, providing insights into the cosmological processes shaping the universe.

Current Challenges in LSB Observations

Traditional surveys such as the Sloan Digital Sky Survey (SDSS) are limited by surface brightness constraints, often failing to capture LSB features below $\mu_{e,r} \sim 23.5$ mag arcsec$^{-2}$. This results in a bias towards brighter galaxies and merger signatures. Observations have indicated that galaxies exhibit more intricate merger-related features at very low surface brightnesses, surpassing $\mu_{r}>27$ mag arcsec$^{-2}$. Addressing these lower limits requires significant technological advancements in imaging and data processing to overcome interference from the night sky, zodiacal light, and instrumental artifacts.

Technological Innovations for LSB Astronomy

Recent advancements in imaging technologies have enabled deeper observations, with techniques such as drift scanning, specialized filter coatings, and optimized data reduction techniques. Notably, surveys like Trujillo et al. demonstrate the emergence of features at surface brightness levels as faint as $\mu_{3,10,10}>31.5$ mag arcsec$^{-2}$, uncovering stellar halos and tidal streams. Furthermore, the discovery of ultra-faint dwarf galaxies has broadened our understanding of galaxy formation and the interaction between dark matter and baryonic processes.

LSST's Contribution to LSB Science

LSST is designed to advance LSB science through its substantial etendue and extended observational timeline, providing depth, a small PSF, and expansive sky coverage. The survey's Wide-Fast-Deep (WFD) initiative and additional mini-surveys will facilitate unprecedented LSB object statistics. The 10-year surface brightness capability, exceeding 32 mag arcsec$^{-2}$, alongside investigations in deep-drilling fields, promises transformative results for LSB features, overcoming current methodological constraints and improving the accuracy and scope of observations.

Intracluster Light and Galaxy Evolution

Understanding the evolution of Brightest Cluster Galaxies (BCGs) is hindered without quantifying the ICL, which encapsulates the interaction history within dense cluster environments. Studies show divergent growth rates for BCGs, challenging theoretical models. By leveraging LSST's large observational sample, spanning various cluster masses and redshifts, researchers can refine models of stellar mass allocation during mergers, contributing to more accurate simulations of galaxy mass evolution.

Addressing Challenges and Future Directions

LSST faces challenges inherent to deep imaging, including light contamination by ghost reflections and galactic cirrus. Innovative sky background subtraction techniques and refined de-blending algorithms are essential. Machine-learning algorithms offer potential solutions for automated identification of LSB features, optimizing the use of large datasets. Collaboration with upcoming missions such as ESA/Euclid and NASA/WFIRST will enrich the dataset, providing complementary observations to expand LSST’s impact.

Conclusion

The Vera Rubin Observatory LSST stands poised to redefine LSB astronomy, offering a robust framework for exploring faint galaxy features and refining our theoretical understanding of galaxy formation and evolution. The insights gained from LSST will guide the next generation of astronomical research, enabling detailed studies of the universe's structure and dynamics. Continued advancements in data processing and collaborative efforts will ensure LSST meets its ambitious objectives, shaping future explorations in cosmic astronomy.