Dark matter scaling relations and the assembly epoch of Coma early-type galaxies

TL;DR

This study uses dynamical models to analyze dark matter properties in Coma early-type galaxies, revealing higher dark matter densities and earlier assembly epochs compared to spiral galaxies, consistent with galaxy formation models.

Contribution

It provides new dark matter scaling relations and estimates of assembly redshifts for Coma early-type galaxies, highlighting differences from spiral galaxies.

Findings

Dark matter halo core-radii increase with galaxy brightness.

Most Coma early-types have larger asymptotic halo velocities than spirals of same brightness.

Estimated assembly redshifts for these galaxies are around z=2-3, earlier than spirals.

Abstract

Axisymmetric, orbit-based dynamical models are used to derive dark matter scaling relations for Coma early-type galaxies. From faint to bright galaxies halo core-radii and asymptotic circular velocities increase. Compared to spirals of the same brightness, the majority of Coma early-types -- those with old stellar populations -- have similar halo core-radii but more than 2 times larger asymptotic halo velocities. The average dark matter density inside 2 reff decreases with increasing luminosity and is 6.8 times larger than in disk galaxies of the same B-band luminosity. Compared at the same stellar mass, dark matter densities in ellipticals are 13.5 times higher than in spirals. Different baryon concentrations in ellipticals and spirals cannot explain the higher dark matter density in ellipticals. Instead, the assembly redshift (1+z) of Coma early-type halos is likely about two times larger than of comparably bright spirals. Assuming that local spirals typically assemble at a redshift of one, the majority of bright Coma early-type galaxy halos must have formed around z = 2-3. For about half of our Coma galaxies the assembly redshifts match with constraints derived from stellar populations. We find dark matter densities and estimated assembly redshifts of our observed Coma galaxies in reasonable agreement with recent semi-analytic galaxy formation models.