Matthew Bershady University of Wisconsin

A small fraction of the universe's energy-density is comprised of normal matter. A still smaller fraction is bound into stars and gas that we can see and are responsible for life. This talk examines what we know about the baryon content of, and how stars assembled in, galaxies like the Milky Way (MW). Dynamical measurements from integral-field spectroscopy indicate the baryonic mass of spiral disks is small. Radiative-transfer modeling of dusty, edge-on galaxies reveals super-thin stellar disks previously missed. These findings yield a consistent picture of light disks with young luminosity-weighted stellar ages. A new census from the Sloan Digital Sky Survey-IV, now underway, will test how broadly these results apply to the galaxy population as a whole. This advance allows us to better place the MW in context of today's galaxy population, and to leverage the MW's unique archaeological record against observations of distant galaxies. A critical question that can be resolved is whether stellar age and abundance gradients in galaxy disks are the result of a settling process of decreasingly turbulent gas or dynamical heating.