The Triangulum Extended (TREX) Survey: The Stellar Disk Dynamics of M33
  as a Function of Stellar Age
  Triangulum, M33, is a low mass, relatively undisturbed spiral galaxy that
offers a new regime in which to test models of dynamical heating. In spite of
its proximity, the dynamical heating history of M33 has not yet been well
constrained. In this work, we present the TREX Survey, the largest stellar
spectroscopic survey across the disk of M33. We present the stellar disk
kinematics as a function of age to study the past and ongoing dynamical heating
of M33. We measure line of sight velocities for ~4,500 disk stars. Using a
subset, we divide the stars into broad age bins using Hubble Space Telescope
and Canada-France-Hawaii-Telescope photometric catalogs: massive main sequence
stars and helium burning stars (~80 Myr), intermediate mass asymptotic branch
stars (~1 Gyr), and low mass red giant branch stars (~4 Gyr). We compare the
stellar disk dynamics to that of the gas using existing HI, CO, and Halpha
kinematics. We find that the disk of M33 has relatively low velocity dispersion
(~16 km/s), and unlike in the Milky Way and Andromeda galaxies, there is no
strong trend in velocity dispersion as a function of stellar age. The youngest
disk stars are as dynamically hot as the oldest disk stars and are dynamically
hotter than predicted by most M33 like low mass simulated analogs in Illustris.
The velocity dispersion of the young stars is highly structured, with the large
velocity dispersion fairly localized. The cause of this high velocity
dispersion is not evident from the observations and simulated analogs presented
here.
