Journal Article

Dynamical Effects of Cold Dark Matter Subhalos on a Galactic Disk

Hirohito Hayashi and Masashi Chiba

in Publications of the Astronomical Society of Japan

Volume 58, issue 5, pages 835-846
Published in print October 2006 | ISSN: 0004-6264
Published online October 2006 | e-ISSN: 2053-051X | DOI: https://dx.doi.org/10.1093/pasj/58.5.835

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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 [math]-body simulations, we find that disk thickening, quantified by the change of its scale height, [math], depends strongly on the individual mass of an interacting subhalo, [math]. This is described by the relation [math], where [math] is the disk scale length, [math] is the disk mass, and [math] is the total number of accretion events of subhalos inside a disk region ([math]). 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, [math] is more affected by subhalos than a disk with a larger [math], in agreement with observations. Further implications of our results for the origin of a thick disk component are also discussed.

Keywords: dark matter; galaxies: formation; galaxies: interactions; galaxies: structure

Journal Article.  8180 words.  Illustrated.

Subjects: Galaxies ; Cosmology