Is dynamic heating of stellar disk inevitable?

TL;DR

This study investigates whether the heating of stellar disks in galaxies is an inevitable consequence of mergers, finding many disks are near stability limits, suggesting mergers may not always be the primary heating mechanism.

Contribution

The paper provides observational evidence that many stellar disks are close to marginal stability, challenging the assumption that mergers are the main cause of disk heating.

Findings

Many stellar disks are near the marginal stability threshold.

Merging processes may not be the primary source of disk heating.

The marginal stability condition can estimate disk mass and densities.

Abstract

Major mergers or/and the repeated minor mergers lead to dynamical heating of disks of galaxies. We analyze the available data on the velocity dispersion of stellar disks of S-S0 galaxies, including the new observational data obtained at 6m telescope of SAO RAS. As a measure of dynamical (over)heating, we use the ratio of the observed velocity dispersion to the minimal dispersion which provides the local stability of the stellar disks with respect to gravitational perturbations. We came to conclusion that stellar disks in a significant part of galaxies (including LSB and some S0 galaxies) are close to the marginal stability condition (or are slightly overheated) -- at least at radial distances $r\sim$ 2-3 radial scalelenghts. It enables to constrain the role of merging in the heating of stellar disks: in many cases it seems to be non-efficient. Marginal stability condition may also be successfully used to estimate the mass of a disk and the midplane volume gas (stars) densities on the basis of kinematic measurements.