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Oscar Agertz. Profile photo.

Oscar Agertz

Assistant Professor / Associate senior university lecturer / Wallenberg Academy Fellow

Oscar Agertz. Profile photo.

EDGE : Two routes to dark matter core formation in ultra-faint dwarfs

Author

  • Matthew D.A. Orkney
  • Justin I. Read
  • Martin P. Rey
  • Imran Nasim
  • Andrew Pontzen
  • Oscar Agertz
  • Stacy Y. Kim
  • Maxime Delorme
  • Walter Dehnen

Summary, in English

In the standard Lambda cold dark matter paradigm, pure dark matter simulations predict dwarf galaxies should inhabit dark matter haloes with a centrally diverging density 'cusp'. This is in conflict with observations that typically favour a constant density 'core'. We investigate this 'cusp-core problem' in 'ultra-faint' dwarf galaxies simulated as part of the 'Engineering Dwarfs at Galaxy formation's Edge' project. We find, similarly to previous work, that gravitational potential fluctuations within the central region of the simulated dwarfs kinematically heat the dark matter particles, lowering the dwarfs' central dark matter density. However, these fluctuations are not exclusively caused by gas inflow/outflow, but also by impulsive heating from minor mergers. We use the genetic modification approach on one of our dwarf's initial conditions to show how a delayed assembly history leads to more late minor mergers and, correspondingly, more dark matter heating. This provides a mechanism by which even ultra-faint dwarfs ($M_∗ \lt 10^5\, \text{M}_{\odot }$), in which star formation was fully quenched at high redshift, can have their central dark matter density lowered over time. In contrast, we find that late major mergers can regenerate a central dark matter cusp, if the merging galaxy had sufficiently little star formation. The combination of these effects leads us to predict significant stochasticity in the central dark matter density slopes of the smallest dwarfs, driven by their unique star formation and mass assembly histories.

Department/s

  • Lund Observatory
  • eSSENCE: The e-Science Collaboration

Publishing year

2021-07-01

Language

English

Pages

3509-3522

Publication/Series

Monthly Notices of the Royal Astronomical Society

Volume

504

Issue

3

Document type

Journal article

Publisher

Oxford University Press

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • dark matter
  • galaxies: dwarf
  • galaxies: evolution
  • galaxies: formation
  • galaxies: haloes
  • methods: numerical

Status

Published

ISBN/ISSN/Other

  • ISSN: 0035-8711