# Imprints of Zero-Age Velocity Dispersions and Dynamical Heating on the Age-Velocity dispersion Relation

## TL;DR

This study uses hydrodynamic simulations to explore how initial stellar velocities and galactic evolution influence the age-velocity dispersion relation, revealing it results from both heating processes and ISM evolution.

## Contribution

The paper demonstrates that the AVR is shaped by both dynamical heating and the historical evolution of the interstellar medium, based on detailed simulations.

## Key findings

- Simulated AVR exponents match observed values.
- AVR is influenced by ISM evolution, not just dynamical heating.
- Stars' velocity dispersions evolve gradually due to ISM changes.

## Abstract

Observations of stars in the the solar vicinity show a clear tendency for old stars to have larger velocity dispersions. This relation is called the age-velocity dispersion relation (AVR) and it is believed to provide insight into the heating history of the Milky Way galaxy. Here, in order to investigate the origin of the AVR, we performed smoothed particle hydrodynamic simulations of the self-gravitating multiphase gas disks in the static disk-halo potentials. Star formation from cold and dense gas is taken into account, and we analyze the evolution of these star particles. We find that exponents of simulated AVR and the ratio of the radial to vertical velocity dispersion are close to the observed values. We also find that the simulated AVR is not a simple consequence of dynamical heating. The evolution tracks of stars with different epochs evolve gradually in the age-velocity dispersion plane as a result of: (1) the decrease in velocity dispersion in star forming regions, and (2) the decrease in the number of cold/dense/gas as scattering sources. These results suggest that the AVR involves not only the heating history of a stellar disk, but also the historical evolution of the ISM in a galaxy.