The Age-velocity Dispersion Relations of the Galactic Disk as Revealed by the LAMOST-Gaia Red Clump Stars

Abstract

Using nearly 230,000 red clump (RC) stars selected from LAMOST and Gaia, we conduct a comprehensive analysis of the stellar age-velocity dispersion relations (AVRs) for various disk populations, within 5.0 $\le$ $R$ $\le$ 15.0 kpc and $|Z|$ $\le$ 3.0 kpc. The AVRs of the whole RC sample stars are accurately described as $\ddot{I}{ƒ}_v$ = $\ddot{I}{ƒ}_{v,0}$ ($\ddot{I}„$ + 0.1)${}^{{\hat{I}}_v^2}$, with ${\hat{I}}_R^2$, ${\hat{I}}_{\ddot{I}}^2•$ and ${\hat{I}}_Z^2$ displaying a global exponential decreasing trend with $R$, which may point to the difference in spatial distributions of various disk heating mechanisms. The measurements of ${\hat{I}}^2$ $-$ $R$ for various disks suggest that the thin disk exhibits a radial dependence, with a global exponential decreasing trend in ${\hat{I}}_R^2$ $-$ $R$ and ${\hat{I}}_Z^2$ $-$ $R$, while ${\hat{I}}_{\ddot{I}}^2•$ remains a nearly constant value (around 0.20$\sim$0.25) within 8.5 $\le$ $R$ $\le$ 11.5 kpc. The thick disk displays a global increasing trend in ${\hat{I}}_R^2$ $-$ $R$, ${\hat{I}}_{\ddot{I}}^2•$ $-$ $R$ and ${\hat{I}}_Z^2$ $-$ $R$. These results indicate that the thin disk stars are likely heated by long-term heating from GMCs and spiral arms, while thick disk stars are likely heated by some violent heating process from merger and accretion, and/or formed by the inside-out and upside-down star formation scenarios, and/or born in the chaotic mergers of gas-rich systems and/or turbulent ISM. Our results also suggest that the disk perturbation by a recent minor merger from Sagittarius may have occurred within 3.0 Gyr.

8 pages, 5 figures, 1 table, accepted for publication in ApJ