Dark Matter Structures in the Universe: Prospects for Optical Astronomy in the Next Decade

TL;DR

This paper discusses the potential of optical astronomy, especially gravitational lensing and wide-field surveys, to test dark matter theories and understand its role in cosmic structure formation over the next decade.

Contribution

It advocates for a comprehensive optical survey approach, combining imaging and spectroscopy, to address key questions about dark matter distribution and nature.

Findings

Gravitational lensing is the most effective probe of dark matter.

Wide-field optical surveys can significantly advance understanding of dark matter.

Combining multiple observational techniques enhances testing of dark matter models.

Abstract

The Cold Dark Matter theory of gravitationally-driven hierarchical structure formation has earned its status as a paradigm by explaining the distribution of matter over large spans of cosmic distance and time. However, its central tenet, that most of the matter in the universe is dark and exotic, is still unproven; the dark matter hypothesis is sufficiently audacious as to continue to warrant a diverse battery of tests. While local searches for dark matter particles or their annihilation signals could prove the existence of the substance itself, studies of cosmological dark matter in situ are vital to fully understand its role in structure formation and evolution. We argue that gravitational lensing provides the cleanest and farthest-reaching probe of dark matter in the universe, which can be combined with other observational techniques to answer the most challenging and exciting questions that will drive the subject in the next decade: What is the distribution of mass on sub-galactic scales? How do galaxy disks form and bulges grow in dark matter halos? How accurate are CDM predictions of halo structure? Can we distinguish between a need for a new substance (dark matter) and a need for new physics (departures from General Relativity)? What is the dark matter made of anyway? We propose that the central tool in this program should be a wide-field optical imaging survey, whose true value is realized with support in the form of high-resolution, cadenced optical/infra-red imaging, and massive-throughput optical spectroscopy.