Red Thick Disks of Nearby Galaxies

Abstract

Edge-on systems reveal the properties of disk galaxies as a function of height, z, above the plane. Four local edge-on galaxies that are close enough to have been resolved into stars by the Hubble Space Telescope show thick disks composed of a red stellar population that is old and relatively metal rich. Color gradients, Δ(V-I)/Δz, are zero or slightly positive. Favored models may have an explicit thick disk formation phase.