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Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses

Campbell, David J.R.; Frenk, Carlos S.; Jenkins, Adrian; Eke, Vincent R.; Navarro, Julio F.; Sawala, Till; Schaller, Matthieu; Fattahi, Azadeh; Oman, Kyle A.; Theuns, Tom

Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses Thumbnail


Authors

David J.R. Campbell

Carlos S. Frenk

Julio F. Navarro

Till Sawala

Matthieu Schaller

Azadeh Fattahi

Kyle A. Oman



Abstract

The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius and the total mass enclosed within the half-light radius, relying on the spherical Jeans equation, have been proposed. Here, we use the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation-supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion-dominated systems with little systematic bias, but with a 1σ scatter of 25 and 23 per cent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro–Frenk–White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 per cent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.

Citation

Campbell, D. J., Frenk, C. S., Jenkins, A., Eke, V. R., Navarro, J. F., Sawala, T., …Theuns, T. (2017). Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses. Monthly Notices of the Royal Astronomical Society, 469(2), 2335-2360. https://doi.org/10.1093/mnras/stx975

Journal Article Type Article
Acceptance Date Apr 21, 2017
Online Publication Date Apr 25, 2017
Publication Date Aug 1, 2017
Deposit Date Jul 5, 2017
Publicly Available Date Jul 5, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 469
Issue 2
Pages 2335-2360
DOI https://doi.org/10.1093/mnras/stx975
Public URL https://durham-repository.worktribe.com/output/1375603

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Copyright Statement
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.






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