Mild Velocity Dispersion Evolution of Spheroid-like Massive Galaxies since z~2

TL;DR

This study measures the velocity dispersion of massive spheroid-like galaxies at z~1.6 and finds a mild decrease over time, suggesting dark matter halos increasingly influence galaxy dynamics at lower redshifts.

Contribution

First measurement of velocity dispersion for spheroid-like massive galaxies at z~1.6, revealing mild evolution contrasting size growth, and highlighting dark matter's role in galaxy evolution.

Findings

Velocity dispersion decreases from ~240 km/s at z~1.6 to ~180 km/s at z~0.

Size increases by a factor of ~4 over the same period.

Dark matter halos increasingly influence galaxy dynamics at lower redshifts.

Abstract

Making use of public spectra from Cimatti et al (2008), we measure for the first time the velocity dispersion of spheroid-like massive (M_star ~ 10^11 M_sun) galaxies at z ~ 1.6. By comparing with galaxies of similar stellar mass at lower redshifts, we find evidence for a mild evolution in velocity dispersion, decreasing from ~240 km/s at z ~ 1.6 down to ~180 km/s at z ~ 0. Such mild evolution contrasts with the strong change in size (a factor of ~4) found for these type of objects in the same cosmic time, and it is consistent with a progressive larger role, at lower redshift, of the dark matter halo in setting the velocity dispersion of these galaxies. We discuss the implications of our results within the context of different scenarios proposed for the evolution of these massive objects.