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The Cluster-EAGLE project: Velocity bias and the velocity dispersion-mass relation of cluster galaxies

Armitage, TJ, Barnes, DJ, Kay, ST, Bahé, YM, Vecchia, CD, Crain, RA and Theuns, T (2017) The Cluster-EAGLE project: Velocity bias and the velocity dispersion-mass relation of cluster galaxies. Monthly Notices of the Royal Astronomical Society, 474 (3). pp. 3746-3759. ISSN 0035-8711

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Abstract

We use the Cluster-EAGLE simulations to explore the velocity bias introduced when using galaxies, rather than dark matter particles, to estimate the velocity dispersion of a galaxy cluster, a property known to be tightly correlated with cluster mass. The simulations consist of 30 clusters spanning a mass range 14.0 ≤ log 10 (M 200 c /M ⊙ ) ≤ 15.4, with their sophisticated subgrid physics modelling and high numerical resolution (subkpc gravitational softening), making them ideal for this purpose. We find that selecting galaxies by their total mass results in a velocity dispersion that is 5-10 per cent higher than the dark matter particles. However, selecting galaxies by their stellar mass results in an almost unbiased ( < 5 per cent) estimator of the velocity dispersion. This result holds out to z = 1.5 and is relatively insensitive to the choice of cluster aperture, varying by less than 5 per cent between r 500 c and r 200m . We show that the velocity bias is a function of the time spent by a galaxy inside the cluster environment. Selecting galaxies by their total mass results in a larger bias because a larger fraction of objects have only recently entered the cluster and these have a velocity bias above unity. Galaxies that entered more than 4 Gyr ago become progressively colder with time, as expected from dynamical friction. We conclude that velocity bias should not be a major issue when estimating cluster masses from kinematic methods.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 25 Jan 2018 10:53
Last Modified: 16 Sep 2018 14:31
DOI or Identification number: 10.1093/mnras/stx3020
URI: http://researchonline.ljmu.ac.uk/id/eprint/7897

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