Science

The observational data from recent years have greatly improved our understanding of the Universe. The fundamental questions that remain to be studied in the coming decades include:

1. How have galaxies evolved? What is the origin of the diversity of galaxies?
2. What is the dark matter that dominates the matter content of the Universe?
3. What is the dark energy that is driving the accelerated expansion of the Universe?
4. What is the 3D structure and stellar content in the dust-enshrouded regions of the Milky Way?
5. What is the census of objects in the outer Solar System?

ATLAS Probe is designed to address these fundamental questions by accomplishing the following:

1. Revolutionize galaxy evolution studies by tracing the relation between galaxies and dark matter from galaxy groups to cosmic voids and filaments, from the epoch of reionization through the peak era of galaxy assembly;
2. Open a new window into the dark Universe by obtaining definitive measurements of dark energy and tests of General Relativity using galaxy clustering, and weighing the dark matter filaments in the cosmic web using 3D weak lensing,;
3. Probe the Milky Way's dust-enshrouded regions, reaching the far side of our Galaxy;
4. Characterize Kuiper Belt Objects and other planetesimals in the outer Solar Systems.

Roman Space Telescope will provide the imaging data which ATLAS Probe will complement and enhance with spectroscopic data. ATLAS Probe will dramatically boost the science from Roman by obtaining slit spectra of ~200M galaxies imaged by Roman with 0.5 < z < 7. ATLAS Probe and Roman together will produce a 3D map of the Universe with sub-Mpc resolution in redshift space over 2000 sq deg, the definitive data sets for studying galaxy evolution, probing dark matter, dark energy and modification of General Relativity, and quantify the 3D structure and stellar content of the Milky Way.

The goals of ATLAS probe can be quantified into four main scientific objectives:

1. Trace the relation between galaxies and dark matter with less than 10% shot noise on relevant scales at 1 < z < 6.
2. Measure cosmic expansion history with 1% precision and linear growth rate with 2% precision in 0.2 redshift bins at 0.5 < z < 3.
3. Measure the dust-enshrouded 3D structure and stellar content of the Milky Way to a distance of 25kpc.
4. Probe the formation history of the outer Solar System through the composition of ~3,000 comets and asteroids.

The ATLAS science objectives flow down to three galaxy surveys nested by area and depth (ATLAS Wide, ATLAS Medium, ATLAS Deep), a Galactic Plane Survey, and a Solar System Survey.