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EDGE : the shape of dark matter haloes in the faintest galaxies

Orkney, Matthew D.A. ; Taylor, Ethan ; Read, Justin I. ; Rey, Martin P. LU ; Pontzen, A. ; Agertz, Oscar LU ; Kim, Stacy Y. and Delorme, Maxime (2023) In Monthly Notices of the Royal Astronomical Society 525(3). p.3516-3532
Abstract

Collisionless dark matter only (DMO) structure formation simulations predict that dark matter (DM) haloes are prolate in their centres and triaxial towards their outskirts. The addition of gas condensation transforms the central DM shape to be rounder and more oblate. It is not clear, however, whether such shape transformations occur in 'ultra-faint' dwarfs, which have extremely low baryon fractions. We present the first study of the shape and velocity anisotropy of ultra-faint dwarf galaxies that have gas mass fractions of fgas(r < Rhalf) < 0.06. These dwarfs are drawn from the Engineering Dwarfs at Galaxy formation's Edge (EDGE) project, using high-resolution simulations that allow us to resolve DM halo... (More)

Collisionless dark matter only (DMO) structure formation simulations predict that dark matter (DM) haloes are prolate in their centres and triaxial towards their outskirts. The addition of gas condensation transforms the central DM shape to be rounder and more oblate. It is not clear, however, whether such shape transformations occur in 'ultra-faint' dwarfs, which have extremely low baryon fractions. We present the first study of the shape and velocity anisotropy of ultra-faint dwarf galaxies that have gas mass fractions of fgas(r < Rhalf) < 0.06. These dwarfs are drawn from the Engineering Dwarfs at Galaxy formation's Edge (EDGE) project, using high-resolution simulations that allow us to resolve DM halo shapes within the half-light radius (∼100 pc). We show that gas-poor ultra-faints (M200c ≤ 1.5 × 109 M⊙; fgas < 10-5) retain their pristine prolate DM halo shape even when gas, star formation, and feedback are included. This could provide a new and robust test of DM models. By contrast, gas-rich ultra-faints (M200c > 3 × 109 M⊙; fgas > 10-4) become rounder and more oblate within ∼10 half-light radii. Finally, we find that most of our simulated dwarfs have significant radial velocity anisotropy that rises to at R 3Rhalf. The one exception is a dwarf that forms a rotating gas/stellar disc because of a planar, major merger. Such strong anisotropy should be taken into account when building mass models of gas-poor ultra-faints.

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author
; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
galaxies: dwarf, galaxies: evolution, galaxies: formation, galaxies: haloes, methods: numerical
in
Monthly Notices of the Royal Astronomical Society
volume
525
issue
3
pages
17 pages
publisher
Oxford University Press
external identifiers
  • scopus:85172695176
ISSN
0035-8711
DOI
10.1093/mnras/stad2516
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
id
6d9b3cbd-5bdb-4c34-919f-f7cc24c19c6e
date added to LUP
2024-01-12 10:05:53
date last changed
2024-04-13 04:20:05
@article{6d9b3cbd-5bdb-4c34-919f-f7cc24c19c6e,
  abstract     = {{<p>Collisionless dark matter only (DMO) structure formation simulations predict that dark matter (DM) haloes are prolate in their centres and triaxial towards their outskirts. The addition of gas condensation transforms the central DM shape to be rounder and more oblate. It is not clear, however, whether such shape transformations occur in 'ultra-faint' dwarfs, which have extremely low baryon fractions. We present the first study of the shape and velocity anisotropy of ultra-faint dwarf galaxies that have gas mass fractions of f<sub>gas</sub>(r &lt; R<sub>half</sub>) &lt; 0.06. These dwarfs are drawn from the Engineering Dwarfs at Galaxy formation's Edge (EDGE) project, using high-resolution simulations that allow us to resolve DM halo shapes within the half-light radius (∼100 pc). We show that gas-poor ultra-faints (M<sub>200c</sub> ≤ 1.5 × 10<sup>9</sup> M<sub>⊙</sub>; f<sub>gas</sub> &lt; 10<sup>-5</sup>) retain their pristine prolate DM halo shape even when gas, star formation, and feedback are included. This could provide a new and robust test of DM models. By contrast, gas-rich ultra-faints (M<sub>200c</sub> &gt; 3 × 10<sup>9</sup> M<sub>⊙</sub>; f<sub>gas</sub> &gt; 10<sup>-4</sup>) become rounder and more oblate within ∼10 half-light radii. Finally, we find that most of our simulated dwarfs have significant radial velocity anisotropy that rises to at R 3R<sub>half</sub>. The one exception is a dwarf that forms a rotating gas/stellar disc because of a planar, major merger. Such strong anisotropy should be taken into account when building mass models of gas-poor ultra-faints.</p>}},
  author       = {{Orkney, Matthew D.A. and Taylor, Ethan and Read, Justin I. and Rey, Martin P. and Pontzen, A. and Agertz, Oscar and Kim, Stacy Y. and Delorme, Maxime}},
  issn         = {{0035-8711}},
  keywords     = {{galaxies: dwarf; galaxies: evolution; galaxies: formation; galaxies: haloes; methods: numerical}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{3}},
  pages        = {{3516--3532}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{EDGE : the shape of dark matter haloes in the faintest galaxies}},
  url          = {{http://dx.doi.org/10.1093/mnras/stad2516}},
  doi          = {{10.1093/mnras/stad2516}},
  volume       = {{525}},
  year         = {{2023}},
}