Cores and the Kinematics of Early-Type Galaxies

TL;DR

This study links the central core structure of early-type galaxies with their rotation velocities, confirming that core galaxies are slow rotators and power-law galaxies are fast rotators, thus aiding in understanding galaxy formation histories.

Contribution

It provides a combined analysis of galaxy core structure and rotation, establishing a clear correlation and refining galaxy classification criteria based on these properties.

Findings

Core galaxies rotate slowly, power-law galaxies rotate rapidly.

Rotation amplitude sharply discriminates between core and power-law galaxies.

Almost all core galaxies have low rotation amplitudes, while high rotation amplitudes lack cores.

Abstract

I have combined the Emsellem et al. ATLAS3D rotation measures of a large sample of early-type galaxies with HST-based classifications of their central structure to characterize the rotation velocities of galaxies with cores. "Core galaxies" rotate slowly, while "power-law galaxies" (galaxies that lack cores) rotate rapidly, confirming the analysis of Faber et al. Significantly, the amplitude of rotation sharply discriminates between the two types in the -19 > Mv > -22 domain over which the two types coexist. The slow rotation in the small set of core galaxies with Mv > -20, in particular, brings them into concordance with the more massive core galaxies. The ATLAS3D "fast-rotating" and "slow-rotating" early-type galaxies are essentially the same as power-law and core galaxies, respectively, or the Kormendy & Bender two families of elliptical galaxies based on rotation, isophote shape, and central structure. The ATLAS3D fast rotators do include roughly half of the core galaxies, but their rotation-amplitudes are always at the lower boundary of that subset. Essentially all core galaxies have ATLAS3D rotation-amplitudes lambda_(R_e/2) <= 0.25, while all galaxies with lambda_(R_e/2) > 0.25 and figure eccentricity > 0.2 lack cores. Both figure rotation and the central structure of early-type galaxies should be used together to separate systems that appear to have formed from "wet" versus "dry" mergers.