Internal and External Alignment of the Shapes and Angular Momenta of ΛCDM Halos

By Jeremy Bailin, Matthias Steinmetz. 2004

312 citations recorded by the source corpus.

We investigate how the shapes and angular momenta of galaxy and group mass dark matter halos in a ΛCDM N-body simulation are correlated internally and how they are aligned with respect to the location and properties of surrounding halos. We explore these relationships down to halos of much lower mass (1011 h-1 M☉) than previous studies. The halos are triaxial, with c/a ratios of 0.6 ± 0.1 and a mean two-dimensional projected ellipticity of = 0.24. More massive halos are more flattened. The axis ratios rise out to 0.6rvir, beyond which they drop. The principal axes, in particular the minor axes, are very well aligned within 0.6 rvir. High-mass halos show particularly strong internal alignment. The angular momentum vectors are also reasonably well aligned except between the very outermost and very innermost regions of the halo. The angular momentum vectors tend to align with the minor axes, with a mean misalignment of ~25°, and lie perpendicular to the major and intermediate axes. The properties of a halo at 0.4 rvir are quite characteristic of the properties at most other radii within the halo. There is a very strong tendency for the minor axes of halos to lie perpendicular to large-scale filaments, and a much weaker tendency for the major axes to lie along the filaments. This alignment extends to much larger separations for group and cluster mass halos than for galaxy mass halos. As a consequence, the intrinsic alignments of galaxies are likely weaker than previous predictions, which were based on the shapes of cluster mass halos. The angular momenta of the highest concentration halos tend to point toward other halos. The angular momenta of galaxy mass halos point parallel to filaments, while those of group and cluster mass halos show a very strong tendency to point perpendicular to the filaments. This suggests that group and cluster mass halos acquire most of their angular momentum from major mergers along filaments, while the accretion history of mass and angular momentum onto galaxy mass halos has been smoother.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/b8ac775fef7b8222fdbd4e039912a4deafb641a6

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Citations in the corpus

Baryonic pinching of galactic dark matter halos (2006, background): “[53] J.”
Statistics of Physical Properties of Dark Matter Clusters (2005, background): “Another way in which the shape of simulated dark matter halos can be classified is in terms of their triaxiality, T (Warren et al. 1992; Bailin & Steinmetz 2005), defined as T a 2 b2 a2 c2 : ð15Þ The full range of triaxiality falls into three regimes: oblate (or ‘‘pancake-like’’) halos correspond…”
THE SPIN AND ORIENTATION OF DARK MATTER HALOS WITHIN COSMIC FILAMENTS (2009, result): “This behavior is in good agreements with previous findings obtained, e.g., by Faltenbacher et al. (2002), Bailin & Steinmetz (2005); Allgood et al. (2006) and Bett et al. (2007).”
The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology (2014, background): “The high-mass galaxy misalignment is due to the merger of galaxies and was suggested by Aubert et al. (2004); Bailin and Steinmetz (2005).”
Spin alignments within the cosmic web: a theory of constrained tidal torques near filaments (2015, methodology): “It has been shown in simulations (Bailin & Steinmetz 2005; Aragón-Calvo et al. 2007; Paz et al. 2008; Zhang et al. 2009; Codis et al. 2012; Libeskind et al. 2013; Forero-Romero et al. 2014, among others) that the spin of dark haloes is correlated to the direction of the filaments of the cosmic web…”
The spin and shape of dark matter haloes in the Millennium simulation of a Λ cold dark matter universe (2006, methodology): “The distribution agrees qualitatively with previous work such as that by Frenk et al. (1988), Warren et al. (1992), Cole & Lacey (1996), Faltenbacher et al. (2002) and Bailin & Steinmetz (2005).”
The Causes of Halo Shape Changes Induced by Cooling Baryons: Disks versus Substructures (2007, background): “…generally triaxial with mean axial ratios b/a ∼ 0.6 and c/a ∼ 0.4, where c < b < a are the short, intermediate, and long axes, respectively (Bardeen et al. 1986; Barnes & Efstathiou 1987; Frenk et al. 1988; Dubinski & Carlberg 1991; Jing & Suto 2002; Bailin & Steinmetz 2005; Allgood et al. 2006).”
The APOSTLE simulations: solutions to the Local Group's cosmic puzzles (2015, methodology): “To characterize the anisotropy of each satellite system, we compute the ratio of the minimal to maximal eigenvalues, c and a, of the reduced inertia tensor (e.g. Bailin & Steinmetz 2005) defined by the 11 brightest satellites, Iα,β = ∑11 i=1 ri,αri,β/r 2 i .”
Connecting the cosmic web to the spin of dark haloes: implications for galaxy formation (2012, background): “It also helps reconciling the findings of Porciani et al. (2002); Lee & Erdogdu (2007) which rely on the tidal tensor with those of Bailin & Steinmetz (2005); Aragón-Calvo et al. (2007); Hahn et al. (2007a); Paz et al. (2008) which involve the density field filamentary structure.”
The evolution of dark matter halo properties in clusters, filaments, sheets and voids (2007, methodology): “We finally compute the spin-spin and spin-orbit correlation functions using the definitions of Porciani et al. (2002) and Bailin & Steinmetz (2005).”
Concentration, spin and shape of dark matter haloes: Scatter and the dependence on mass and environment (2006, result): “We find that more massive haloes are on average more flattened (more prolate), in qualitative agreement with previous studies (Jing & Suto 2002; Bailin & Steinmetz 2005; Kasun & Evrard 2005; Allgood et al. 2006).”
Structure finding in cosmological simulations: the state of affairs (2013, methodology): “Note that the simplest method determines the shape and orientation of a halo using all particles within a spherical volume or shell at a given radius (e.g. Frenk et al. 1988; Bailin & Steinmetz 2005; Hopkins, Bahcall & Bode 2005; Kasun & Evrard 2005).”
CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY (2015, background): “The misalignment angle of the angular momentum vectors at different radii was studied in more detail by Bailin & Steinmetz (2005), who showed that with increasing separation of the radii the misalignment of the vectors increases.”
Bar formation and evolution in disc galaxies with gas and a triaxial halo: morphology, bar strength and halo properties (2012, background): “Yet cosmological simulations (e.g. Dubinski & Carlberg 1991; Jing & Suto 2002; Bailin & Steinmetz 2005; Allgood et al. 2006; Novak et al. 2006; Vera-Ciro et al. 2011; Schneider, Frenk & Cole 2012) have shown that in cases with no baryons the haloes are strongly triaxial, as could be expected by the…”
Evidence for spin alignment of spiral and elliptical/S0 galaxies in filaments (2012, background): “E-mail: elmo@aai.ee During the last years, correlations between dark matter haloes and their host filaments have been detected in N-body simulations (Hatton & Ninin 2001; Faltenbacher et al. 2002; Bailin & Steinmetz 2005; Altay, Colberg & Croft 2006; Brunino et al. 2007; Wang et al. 2011).”
Properties of dark matter haloes in clusters, filaments, sheets and voids (2006, unknown): “We define the spin–spin correlation function as (Porciani, Dekel & Hoffman 2002a; Bailin & Steinmetz 2005) ξJ·J(r ) = 〈 Ĵ(x) · Ĵ(x + r )〉, (20) where J is the intrinsic angular momentum of each halo, and the average is taken over all pairs of haloes which are separated by a distance r and reside…”