Galaxies outside clusters

Through multilinear regression we identified the quantities that, at a fixed mass and environmental density of the galaxy, significantly correlate with a measure of the ordered rotation of the galaxy, lambda^N^_Re_. We found a negative correlation of the rotational support with the occurrence of tidal disturbances and kinematic substructures, and a positive correlation with metallicity and metallicity gradients. For massive galaxies, the rotational support correlates negatively with the abundance of alpha elements, and for the galaxies in low-density environments, it correlates negatively with the central photometric cuspiness.

These and additional literature observational constraints are explained the easiest if the mergers that decreased the rotational support of ETGs were typically minor, wet, and happening at z~2. They did not form the currently observed tid al features. The observed frequency of tidal features implies a merging rate of 0.07-0.2 per Gyr.

This is insufficient to explain the observed growth of the radii of ETGs with redshift by mergers.