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Tidal stripping and the structure of dwarf galaxies in the Local Group

Fattahi, A.; Navarro, J.F.; Frenk, C.S.; Oman, K.A.; Sawala, T.; Schaller, M.

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A. Fattahi

J.F. Navarro

K.A. Oman

T. Sawala

M. Schaller


The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax < 20–30 km s−1. Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo Vmax but their characteristic velocities are well below 20 km s−1. These ‘cold faint giants’ (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy–acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the amin ∼ 10−11 m s−2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.


Fattahi, A., Navarro, J., Frenk, C., Oman, K., Sawala, T., & Schaller, M. (2018). Tidal stripping and the structure of dwarf galaxies in the Local Group. Monthly Notices of the Royal Astronomical Society, 476(3), 3816-3836.

Journal Article Type Article
Acceptance Date Feb 14, 2018
Online Publication Date Feb 19, 2018
Publication Date May 21, 2018
Deposit Date Apr 5, 2018
Publicly Available Date Apr 6, 2018
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 476
Issue 3
Pages 3816-3836


Published Journal Article (2.1 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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