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 in galaxies thought to be like the Milky Way (MW). Baryon mass fractions measured dynamically with integral-field spectroscopy are lower than what is found in recent studies of the MW. However, radiative-transfer modeling of dusty, edge-on galaxies reveals super-thin stellar disks previously missed. These findings yield a consistent picture of dynamically light disks with young luminosity-weighted ages; they pose challenges for stellar population synthesis and our canonical picture of disk star-formation histories. The MW could be unusual, or alternatively, photometric estimates of galaxy length-scales grossly mismatch the distribution of dynamical tracers. A new census from the Sloan Digital Sky Survey-IV will test these results and alternatives across the galaxy population as a whole.
Matthew Bershady (University of Wisconsin-Madison)
January 16, 2015
14:00 - 15:00