The stellar halos of massive elliptical galaxies. III. Kinematics at large radius

Abstract

We present a two-dimensional kinematic analysis out to ∼2-5 effective radii (Re) of 33 massive elliptical galaxies with stellar velocity dispersions σ > 150 km s-1. Our observations were taken using the Mitchell Spectrograph (formerly VIRUS-P), a spectrograph with a large 107 × 107 arcsec2 field of view that allows us to construct robust, spatially resolved kinematic maps of V and σ for each galaxy extending to at least 2 Re . Using these maps, we study the radial dependence of the stellar angular momentum and other kinematic properties. We see the familiar division between slow and fast rotators persisting out to a large radius in our sample. Centrally slow rotating galaxies, which are almost universally characterized by some form of kinematic decoupling or misalignment, remain slowly rotating in their halos. The majority of fast-rotating galaxies show either increases in specific angular momentum outward or no change beyond Re . The generally triaxial nature of the slow rotators suggests that they formed through mergers, consistent with a "two-phase" picture of elliptical galaxy formation. However, we do not observe the sharp transitions in kinematics proposed in the literature as a signpost of moving from central dissipationally formed components to outer accretion-dominated halos. © 2014. The American Astronomical Society. All rights reserved.