The Mystery of the $\sigma$-Bump -- A new Signature for Major Mergers in Early-type Galaxies?

Abstract

The stellar velocity dispersion as a function of the galactocentric radius of an early-type galaxy can generally be well approximated by a power law $\sigma \propto r^{\beta }$. However, some observed dispersion profiles show a deviation from this fit at intermediate radii, usually between one and three $R_{\mathrm{eff}}$, where the velocity dispersion remains constant with radius, showing a bump-like behavior, which we term the "$\sigma$-"bump. To understand the origin of this $\sigma$-bump, we study a set of simulated early-type galaxies formed in major mergers. We find the $\sigma$-bump in all of our simulated early-type galaxies, with the size and position of the bump slightly varying from galaxy to galaxy, leading to the assumption that the bump is a characteristic of the major merger formation scenario. The feature can be seen both in the intrinsic and projected stellar velocity dispersions. In contrast to shells that form during the merger event but evolve with time and finally disappear, the $\sigma$-bump stays nearly constant with radius and is a permanent feature that is preserved until the end of the simulation. The $\sigma$-bump is not seen in the dark matter and gas components and we therefore conclude that it is a purely stellar feature of merger remnants.

7 pages, 4 figures, submitted to APJ Letters

References in corpus (7)

• Equal- and unequal-mass mergers of disk and elliptical galaxies with black holes
• Kinematic properties of early-type galaxy haloes using planetary nebulae
• 2-Dimensional Kinematics of Simulated Disc Merger Remnants
• The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494
• Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023
• The SLUGGS Survey: outer triaxiality of the Fast Rotator elliptical NGC 4473
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• The SLUGGS Survey: The Assembly Histories of Individual Early-type Galaxies
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