Small scatter and nearly isothermal mass profiles to four half-light radii from two-dimensional stellar dynamics of early-type galaxies

Michele Cappellari, Aaron J. Romanowsky, Jean P. Brodie, Duncan A. Forbes, Jay Strader, Caroline Foster, Sreeja S. Kartha, Nicola Pastorello, Vincenzo Pota, Lee R. Spitler, Christopher Usher, Jacob A. Arnold

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    We study the total mass-density profile for a sample of 14 fast-rotator early-type galaxies (stellar masses ). We combine observations from the SLUGGS and ATLAS surveys to map out the stellar kinematics in two dimensions, out to a median radius for the sample of four half-light radii Re (or 10 kpc) and a maximum radius of 2.0-6.2 Re (or 4-21 kpc). We use axisymmetric dynamical models based on the Jeans equations, which allow for a spatially varying anisotropy; employ quite general profiles for the dark halos; and, in particular, do not place any restrictions on the profile slope. This is made possible by the availability of spatially extended two-dimensional kinematics. We find that our relatively simple models provide a remarkably good description of the observed kinematics. The resulting total density profiles are well described by a nearly isothermal power law from Re/10 to at least 4Re, the largest average deviation being 11%. The average logarithmic slope is with observed rms scatter of just . This scatter out to large radii, where dark matter dominates, is as small as previously reported by lensing studies around r ≈ Re/2, where the stars dominate. Our bulge-halo conspiracy places much tighter constraints on galaxy formation models. It illustrates the power of two-dimensional stellar kinematics observations at large radii. It is now important to test the generality of our results for different galaxy types and larger samples.

    Original languageEnglish
    Article numberL21
    Pages (from-to)1-7
    Number of pages7
    JournalAstrophysical Journal Letters
    Issue number1
    Publication statusPublished - 1 May 2015

    Bibliographical note

    Copyright 2015 The American Astronomical Society. First published in the Astrophysical journal letters, 804(1), L21, 2015, published by IOP Publishing. The original publication is available at Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


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