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The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

Frenk, Carlos S; Belokurov, Vasily; Deason, Alis J; Bose, Sownak

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Authors

Vasily Belokurov

Sownak Bose



Abstract

Ultrafaint dwarf galaxies (M⋆ ≤ 105 M⊙) are relics of an early phase of galaxy formation. They contain some of the oldest and most metal-poor stars in the Universe which likely formed before the epoch of hydrogen reionisation. These galaxies are so faint that they can only be detected as satellites of the Milky Way. They are so small that they are not resolved in current cosmological hydrodynamics simulations. Here we combine very high resolution cosmological N-body simulations with a semi-analytic model of galaxy formation to study the demographics and spatial distribution of ultrafaint satellites in Milky Way-mass haloes. We show that the abundance of these galaxies is correlated with the assembly history of the host halo: at fixed mass, haloes assembled earlier contain, on average, more ultrafaint satellites today than haloes assembled later. We identify simulated galactic haloes that experience an ancient Gaia-Enceladus-Sausage-like and a recent LMC-like accretion event and find that the former occurs in 33% of the sample and the latter in 9%. Only 3% experience both events and these are especially rich in ultrafaint satellites, most acquired during the ancient accretion event. Our models predict that the radial distribution of satellites is more centrally concentrated in early-forming haloes. Accounting for the depletion of satellites by tidal interactions with the central disc, we find a very good match to the observed radial distribution of satellites in the Milky Way over the entire radial range. This agreement is mainly due to the ability of our model to track ‘orphan’ galaxies after their subhaloes fall below the resolution limit of the simulation.

Citation

Frenk, C. S., Belokurov, V., Deason, A. J., & Bose, S. (2020). The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history. Monthly Notices of the Royal Astronomical Society, 495(1), 743-757. https://doi.org/10.1093/mnras/staa1199

Journal Article Type Article
Acceptance Date Apr 25, 2020
Online Publication Date May 4, 2020
Publication Date Jun 30, 2020
Deposit Date May 5, 2020
Publicly Available Date May 5, 2020
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 495
Issue 1
Pages 743-757
DOI https://doi.org/10.1093/mnras/staa1199

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Copyright Statement
Advance online version This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2020 The Author(s) . Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






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