Dynamical effects of cold dark matter subhalos on a galactic disk

Hirohito Hayashi, Masashi Chiba

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)


We have investigated the dynamical interaction between a galactic disk and numerous surrounding dark subhalos as expected for a galaxy-sized halo in the cold dark matter models. Our particular interest is to what extent accretion events of subhalos into a disk are allowed in light of the observed thinness of a disk. Several models of subhalos were considered in terms of their internal density distribution, mass function, and spatial and velocity distributions. Based on a series of N-body simulations, we find that disk thickening, quantified by the change of its scale height, Δzd, depends strongly on the individual mass of an interacting subhalo, Msub. This is described by the relation Δzd/Rd ≃ 8 Σj=1N(Msub,j/Md)2, where Rd is the disk scale length, Md is the disk mass, and N is the total number of accretion events of subhalos inside a disk region (≤ 3 Rd). Using this relation, we find that an observed thin disk has never interacted with subhalos with a total mass of more than 15% of the disk mass. Also, a less-massive disk with a smaller circular velocity, V c is more affected by subhalos than a disk with a larger V c, in agreement with observations. Further implications of our results for the origin of a thick disk component are also discussed.

Original languageEnglish
Pages (from-to)835-846
Number of pages12
JournalPublication of the Astronomical Society of Japan
Issue number5
Publication statusPublished - 2006


  • Cosmology: dark matter
  • Galaxies: formation
  • Galaxies: interactions
  • Galaxies: structure


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