Princeton University Star Formation/ISM Rendezvous (SFIR)

It is generally agreed upon that the Milky Way has spiral arms but their number and nature are still under debate. The spiral arms are considered to be either quasi-stationary density waves or material arms that form and dissipate over one to several Galactic rotation periods. These two models of spiral structure make qualitatively different predictions for the velocity fields of the gaseous spiral arms. To determine which description of spiral structure applies to the Milky Way, we have mapped the velocity field of interstellar gas and dust as a function of location in the Galactic plane. By comparing these maps with simulations of spiral structure in Milky Way like galaxies, we have found that the Milky Way most likely has material rather than density wave spiral arms and that part of the Perseus spiral arm is in the process of coming apart.