Document Type

Article

Publication Date

January 2014

Publication Title

Monthly Notices of the Royal Astronomical Society

Volume

442

Issue Number

4

First Page

3284

Last Page

3298

DOI

10.1093/mnras/stu959

Keywords

methods: analytical, methods: numerical, galaxies: kinematics and dynamics, dark matter

Disciplines

Astrophysics and Astronomy | External Galaxies

Abstract

We study dynamical models for elliptical galaxies, deriving the projected kinematic profiles in a form that is valid for general surface-brightness profiles and (spherical) total mass profiles, without the need for any explicit deprojection. We then show that an almost flat rotation curve, combined with modest velocity anisotropy, is already sufficient to recover the kinematic profiles of nearby ellipticals. As an application, we provide two different sets of mass estimators for elliptical galaxies, based on either the velocity dispersion at a specific location near the effective radius, or the aperture-averaged velocity dispersion. In the large aperture (virial) limit, mass estimators are naturally independent of anisotropy. The spherical mass enclosed within the effective radius Re can be estimated as 2.4Re⟨σ2p⟩/G, where ⟨σ2p⟩ is the average of the squared velocity dispersion over a finite aperture. This formula does not depend on assumptions such as mass-follows-light, and is a compromise between the cases of small and large apertures sizes. Its general agreement with results from other methods in the literature makes it a reliable means to infer masses in the absence of detailed kinematic information. If on the other hand the velocity dispersion profile is available, tight mass estimates can be found that are independent of the mass-model and anisotropy profile (within ≈ 10\% accuracy). Explicit formulae are given for small anisotropy, large radii and/or power-law total densities. Motivated by recent observational claims, we also discuss the issue of weak homology of elliptical galaxies, emphasizing the interplay between morphology and orbital structure.

Comments

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2014. Published by Oxford University Press on behalf of Monthly Notices of the Royal Astronomical Society . All rights reserved.The Version of Record is also available online here: https://doi.org/10.1093/mnras/stu959

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