Disk Heating: Comparing the Milky Way with Cosmological Simulations

We present the analysis of a suite of disk galaxy simulations run with different particle- and grid-based cosmological hydrodynamical codes and compare them with observational data of the Milky Way. We study the velocity dispersion versus age for disk stars at z = 0 and find that some of the simulations are more consistent with observations by [1] where the stellar disk appears to undergo continual/secular heating. Two other simulations are in better agreement with the [2] observations that suggest a "saturation" in the heating profile for young stars in the disk. We also analyse the kinematics of disk stars at the time of their birth and find that in some simulations stars are born cold within the disk and heat due to a combination of physical and/or numerical processes, while other simulations present little heating of the disk with time. Two of the models which are in better agreement with observations of the Milky Way's stellar disk undergo significantly lower minor-merger/assembly activity after the last major merger, i.e. once the disk has formed. All of the simulations are significantly "hotter" than the Milky Way disk, a problem likely rooted in the underlying treatment of the interstellar medium.