Substructure Depletion in the Milky Way Halo by the Disk

Abstract

We employ numerical simulations and simple analytical estimates to argue that dark matter substructures orbiting in the inner regions of the Galaxy can be efficiently destroyed by disk shocking, a dynamical process known to affect globular star clusters. We carry out a set of fiducial high-resolution collisionless simulations in which we adiabatically grow a disk, allowing us to examine the impact of the disk on the substructure abundance. We also track the orbits of dark matter satellites in the high-resolution Aquarius simulations and analytically estimate the cumulative halo and disk shocking effect. Our calculations indicate that the presence of a disk with only 10% of the total Milky Way mass can significantly alter the mass function of substructures in the inner parts of halos. This has important implications especially for the relatively small number of satellites seen within ∼30 kpc of the Milky Way center, where disk shocking is expected to reduce the substructure abundance by a factor of 2 at 10 9 M ⊙ and 3 at 10 7 M ⊙ . The most massive subhalos with 10 10 M ⊙ survive even in the presence of the disk. This suggests that there is no inner missing satellite problem, and calls into question whether these substructures can produce transient features in disks, like multi-armed spiral patterns. Also, the depletion of dark matter substructures through shocking on the baryonic structures of the disk and central bulge may aggravate the problem to fully account for the observed flux anomalies in gravitational lens systems, and significantly reduces the dark matter annihilation signal expected from nearby substructures in the inner halo.

Subhalo demographics in the Illustris simulation: effects of baryons and halo-to-halo variation

“…Specifically for disk galaxies, it has been found in single zoom-in simulations that the presence of discs can gravitionally shock subhaloes during disc passages and lead to additional subhalo destruction (D'Onghia et al 2010;Yurin & Springel 2015).…”

Stellar spiral structures in triaxial dark matter haloes

“…Analysing high resolution Aquarius simulations (Springel et al 2008), Vera-Ciro et al (2011) showed that due to the cosmic growth history of dark matter haloes, their triaxiality can change rapidly over time, implying that the disc will be subject to a timedependent torque. It is generally believed that the inclusion of baryons leads to a reduction of halo triaxiality (Dubinski 1994;D'Onghia et al 2010;Zemp et al 2012;Bryan et al 2013;Zhu et al 2016), with haloes becoming more oblate, especially in the central region. However, the resulting mildly triaxial halo mass distribution may still impart a significant torque on to the disc of the central galaxy.…”

An iterative method for the construction of N-body galaxy models in collisionless equilibrium

“…They are also actively used to study the response of disks to the bombardment by dark matter clumps (e.g. Kazantzidis et al 2008;D'Onghia et al 2010), or the radial migration of stars caused by resonance scattering (e.g. Sellwood & Binney 2002), and many more.…”