Bar-Halo Friction in Galaxies III: Halo Density Changes

Abstract

The predicted central densities of dark matter halos in LCDM models exceed those observed in some galaxies. Weinberg & Katz argue that angular momentum transfer from a rotating bar in the baryonic disk can lower the halo density, but they also contend that N-body simulations of this process will not reveal the true continuum result unless many more than the usual numbers of particles are employed. Adopting their simplified model of a rotating rigid bar in a live halo, I have been unable to find any evidence to support their contention. I find that both the angular momentum transferred and the halo density change are independent of the number of particles over the range usually employed up to that advocated by these authors. I show that my results do not depend on any numerical parameters, and that field methods perform equally with grid methods. I also identify the reasons that the required particle number suggested by Weinberg & Katz is excessive. I further show that when countervailing compression by baryonic settling is ignored, moderate bars can reduce the mean density of the inner halo by 20% - 30%. Long, massive, skinny bars can reduce the mean inner density by a factor ~10. The largest density reductions are achieved at the expense of removing most of the angular momentum likely to reside in the baryonic component. Compression of the halo by baryonic settling must reduce, and may even overwhelm, the density reduction achievable by bar friction.

19 pages, 16 figures, uses emulateapj, accepted to appear in ApJ. Extensively revised from v1

References in corpus (6)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Cosmological Constraints from the SDSS Luminous Red Galaxies
• High Resolution Optical Velocity Fields of 11 Low Surface Brightness Galaxies
• Resonances in Barred Galaxies
• Photometric Decomposition of Barred Galaxies
• Modeling the Gas Flow in the Bar of NGC 1365

Cited by in corpus (16)

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• Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
• Early flattening of dark matter cusps in dwarf spheroidal galaxies
• Tree-ring structure of Galactic bar resonance
• Tests and problems of the standard model in Cosmology
• The rapid onset of stellar bars in the baryon-dominated centers of disk galaxies
• Bars and spirals in tidal interactions with an ensemble of galaxy mass models
• Halo density reduction by baryonic settling?
• The global stability of M33: still a puzzle
• The structural evolution of galaxies with both thin and thick discs
• Multi-mass schemes for collisionless N-body simulations
• Numerical simulations of bar formation in the Local Group
• A slow lopsided bar in the interacting dwarf galaxy IC 3167
• The Tully-Fisher Zero Point Problem
• Made-To-Measure Models of Self-Similar Triaxial Halos with Steep Inner Density Gradients
• Baryon-driven decontraction in Milky Way mass haloes