Major mergers between dark matter haloes -- II. Profile and concentration changes

Abstract

Several lines of evidence suggest that as dark matter haloes grow their scale radius increases, and that the density in their central region drops. Major mergers seem an obvious mechanism to explain both these phenomena, and the resulting patterns in the concentration--mass--redshift relation. To test this possibility, we have simulated equal-mass mergers between haloes with a variety of cosmological density profiles, placed on various different orbits. The remnants typically have higher densities than the initial conditions, but differ only slightly from self-similar scaling predictions. They are reasonably well fit by Einasto profiles, but have parameters distinct from those of the initial conditions. The net internal energy available to the merger remnant, relative to the internal energy of the initial conditions, $\kappa$, has the greatest influence on the properties of the final mass distribution. As expected, energetic encounters produce more extended remnants while mergers of strongly bound systems produce compact remnants. Surprisingly, however, the scale radius of the density profile shows the opposite trend, {\it increasing} in the remnants of low-energy encounters relative to energetic ones. Also even in the most energetic encounters, the density within the scale radius decreases only slightly (by 10--20\%), while for very low-energy systems it increases significantly after the merger. We conclude that while major mergers can produce remnants that are more diffuse at large radii, they are relatively ineffective at changing the central densities of haloes, and seem unlikely to explain the mean trends in the concentration--mass--redshift relation.

19 pages, 16 figures; accepted for publication, MNRAS

References in corpus (35)

• The cosmological simulation code GADGET-2
• Profiles of dark haloes: evolution, scatter, and environment
• The Inner Structure of LambdaCDM Halos III: Universality and Asymptotic Slopes
• MultiDark simulations: the story of dark matter halo concentrations and density profiles
• Cold dark matter haloes in the Planck era: evolution of structural parameters for Einasto and NFW profiles
• Dark matter halo concentrations in the Wilkinson Microwave Anisotropy Probe year 5 cosmology
• The statistics of LCDM Halo Concentrations
• Halo concentrations in the standard LCDM cosmology
• Formation and evolution of galaxy dark matter halos and their substructure
• The redshift dependence of the structure of massive LCDM halos
• Accurate universal models for the mass accretion histories and concentrations of dark matter halos
• The Growth and Structure of Dark Matter Haloes
• The Universal Mass Accretion History of CDM Haloes
• CLASH: Joint Analysis of Strong-Lensing, Weak-Lensing Shear and Magnification Data for 20 Galaxy Clusters
• The pseudo-evolution of halo mass
• The MUSIC of CLASH: predictions on the concentration-mass relation
• Hierarchical Formation of Dark Matter Halos and the Free Streaming Scale
• The Robustness of Dark Matter Density Profiles in Dissipationless Mergers
• Not too big, not too small: the dark halos of the dwarf spheroidals in the Milky Way
• Major Mergers of Galaxy Haloes: Cuspy or Cored Inner Density Profile?
• The origin and tidal evolution of cuspy triaxial haloes
• The shape of dark matter subhalos in the Aquarius simulations
• Multimass spherical structure models for N-body simulations
• Satellite Galaxy Number Density Profiles in the Sloan Digital Sky Survey
• What Do Dark Matter Properties Tell Us About Their Mass Assembly Histories?
• Dynamical Evolution of Primordial Dark Matter Haloes through Mergers
• The phase-space structure of tidally stripped halos
• On relaxation processes in collisionless mergers
• The Spectroscopy and H-band Imaging of Virgo cluster galaxies (SHIVir) Survey: Scaling Relations and the Stellar-to-Total Mass Relation
• The haloes of merger remnants
• Pushing down the low-mass halo concentration frontier with the Lomonosov cosmological simulations
• Major mergers between dark matter haloes -- I. Predictions for size, shape, and spin
• Evolution of Dark Matter Phase-Space Density Distributions in Equal-Mass Halo Mergers
• Searching for dark matter annihilation from individual halos: uncertainties, scatter and signal-to-noise ratios
• Preservation of Cuspy Profiles in Disk Galaxy Mergers

Cited by in corpus (17)

• Quantifying the impact of the Large Magellanic Cloud on the structure of the Milky Way's dark matter halo using Basis Function Expansions
• Breaking a dark degeneracy: The gamma-ray signature of early matter domination
• The Secondary Spin Bias of Dark Matter Haloes
• Mass loss in tidally stripped systems; the energy-based truncation method
• ProFuse: Physical Multi-Band Structural Decomposition of Galaxies and the Mass-Size-Age Plane
• Lensing constraints on ultradense dark matter halos
• The Three Hundred project: galaxy cluster mergers and their impact on the stellar component of brightest cluster galaxies
• Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination
• Major mergers between dark matter haloes -- I. Predictions for size, shape, and spin
• Dark matter cores in massive high-$z$ galaxies formed by baryonic clumps
• How an era of kination impacts substructure and the dark matter annihilation rate
• A universal model for the evolution of tidally stripped systems
• Cluster Assembly Times as a Cosmological Test
• Toward More Realistic Mass Functions For Ultradense Dark Matter Halos
• Dissociation of dark matter and gas in cosmic large-scale structure
• 21-cm Constraints on Dark Matter Annihilation after an Early Matter-Dominated Era
• Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection