The outer halos of elliptical galaxies
Ortwin Gerhard (MPE)

TL;DR
This paper reviews recent advances in understanding the structure, dynamics, and stellar populations of elliptical galaxy halos, highlighting complex kinematic features, dark matter profiles, and environmental influences.
Contribution
It provides a comprehensive summary of observational and dynamical studies of elliptical galaxy halos, emphasizing new findings on their kinematics, dark matter distribution, and stellar populations.
Findings
Velocity dispersion profiles extend to 4-8 effective radii.
Inner dark matter densities are higher than in spiral galaxies.
Evidence suggests ongoing accretion influences halo properties.
Abstract
Recent progress is summarized on the determination of the density distributions of stars and dark matter, stellar kinematics, and stellar population properties, in the extended, low surface brightness halo regions of elliptical galaxies. With integral field absorption spectroscopy and with planetary nebulae as tracers, velocity dispersion and rotation profiles have been followed to ~4 and ~5-8 effective radii, respectively, and in M87 to the outer edge at ~150 kpc. The results are generally consistent with the known dichotomy of elliptical galaxy types, but some galaxies show more complex rotation profiles in their halos and there is a higher incidence of misalignments, indicating triaxiality. Dynamical models have shown a range of slopes for the total mass profiles, and that the inner dark matter densities in ellipticals are higher than in spiral galaxies, indicating earlier assembly…
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