Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph

The Subaru Prime Focus Spectrograph (PFS) is a massively multiplexed fiber-fed optical and near-infrared three-arm spectrograph (N_fiber= 2400, 380 ≤ λ ≤ 1260 nm, 13 diameter field of view). Here, we summarize the science cases in terms of provisional plans for a 300-night Subaru survey. We describe plans to constrain the nature of dark energy via a survey of emission line galaxies spanning a comoving volume of 9.3 h^-3Gpc³in the redshift range 0.8 < z < 2.4. In each of six redshift bins, the cosmological distances will be measured to 3% precision via the baryonic acoustic oscillation scale, and redshift-space distortion measures will constrain structure growth to 6% precision. In the near-field cosmology program, radial velocities and chemical abundances of stars in the Milky Way and M 31 will be used to infer the past assembly histories of spiral galaxies and the structure of their dark matter halos. Data will be secured for 10⁶stars in the Galactic thick-disk, halo, and tidal streams as faint as V ∼ 22, including stars with V < 20 to complement the goals of the Gaia mission. A medium-resolution mode with R = 5000 to be implemented in the red arm will allow the measurement of multiple α-element abundances and more precise velocities for Galactic stars. For the galaxy evolution program, our simulations suggest the wide wavelength range of PFS will be powerful in probing the galaxy population and its clustering over a wide redshift range. We plan to conduct a color-selected survey of 1 < z < 2 galaxies and AGN over 16 deg²to J ≃ 23.4, yielding a fair sample of galaxies with stellar masses above ∼10¹⁰M_ȯat z ≃ 2. A two-tiered survey of higher redshift Lyman break galaxies and Lyman alpha emitters will quantify the properties of early systems close to the reionization epoch.