  ATLAS (Astrophysics Telescope for Large Area Spectroscopy) is a concept for a
NASA probe-class space mission. It is the spectroscopic follow-up mission to
WFIRST, boosting its scientific return by obtaining deep NIR & MIR slit
spectroscopy for most of the galaxies imaged by the WFIRST High Latitude Survey
at z>0.5. ATLAS will measure accurate and precise redshifts for ~200M galaxies
out to z=7 and beyond, and deliver spectra that enable a wide range of
diagnostic studies of the physical properties of galaxies over most of cosmic
history. ATLAS and WFIRST together will produce a definitive 3D map of the
Universe over 2000 sq deg. ATLAS Science Goals are: (1) Discover how galaxies
have evolved in the cosmic web of dark matter from cosmic dawn through the peak
era of galaxy assembly. (2) Discover the nature of cosmic acceleration. (3)
Probe the Milky Way's dust-enshrouded regions, reaching the far side of our
Galaxy. (4) Discover the bulk compositional building blocks of planetesimals
formed in the outer Solar System. These flow down to the ATLAS Scientific
Objectives: (1A) Trace the relation between galaxies and dark matter with less
than 10% shot noise on relevant scales at 1<z<7. (1B) Probe the physics of
galaxy evolution at 1<z<7. (2) Obtain definitive measurements of dark energy
and tests of General Relativity. (3) Measure the 3D structure and stellar
content of the inner Milky Way to a distance of 25 kpc. (4) Detect and quantify
the composition of 3,000 planetesimals in the outer Solar System. ATLAS is a
1.5m telescope with a FoV of 0.4 sq deg, and uses Digital Micro-mirror Devices
(DMDs) as slit selectors. It has a spectroscopic resolution of R = 1000, and a
wavelength range of 1-4 microns. ATLAS has an unprecedented spectroscopic
capability based on DMDs, with a spectroscopic multiplex factor ~6,000. ATLAS
is designed to fit within the NASA probe-class space mission cost envelope.
