Vertical motions of APOGEE & Gaia red clump stars

Here we map the vertical actions of disk stars as a function of age ({tau}<=8Gyr) and across a large range of Galactocentric radii, R_GC_, drawing on APOGEE and Gaia data. We fit J_z_(R_GC,{tau}_) as a combination of the vertical action at birth, J_z,0_, and the subsequent heating {Delta}J_z,1Gyr_(R_GC_), which scales as {tau}^{gamma}(R_GC_)^.

The inferred birth temperature, J_z,0_(R_GC_) is 1kpc.km/s for 3kpc<R_GC_<10kpc, consistent with the ISM velocity dispersion, but it rapidly rises outward, to 8kpc.km/s for R_GC_=14kpc, likely reflecting the stars' birth in a warped or flared gas disk. We find the heating rate {Delta}J_z,1Gyr_ to be modest and nearly constant across all radii, 1.6kpc.km/s/Gyr. The stellar age dependence {gamma} gently grows with Galactocentric radius, from {gamma}~1 for R_GC_<~R_{sun}_ to {gamma}~1.3 at R_GC_=14kpc.