Red Thick Disks of Nearby Galaxies

Edge on systems reveal the properties of disk galaxies as a function ofheight, z, above the plane. Four local edge-on galaxies, that are close enoughto have been resolved into stars by the Hubble Space Telescope, show thickdisks, composed of a red stellar population, which is old and relatively metalrich. Color gradients, d(V-I)/dz, are zero or slightly positive. Favored modelsmay have an explicit thick disk formation phase