The effects of halo alignment and shape on the clustering of galaxies

Abstract

We investigate the effects of halo shape and its alignment with larger scale structure on the galaxy correlation function. We base our analysis on the galaxy formation models of Guo et al., run on the Millennium Simulations. We quantify the importance of these effects by randomizing the angular positions of satellite galaxies within haloes, either coherently or individually, while keeping the distance to their respective central galaxies fixed. We find that the effect of disrupting the alignment with larger scale structure is a ~2 per cent decrease in the galaxy correlation function around r=1.8 Mpc/h. We find that sphericalizing the ellipsoidal distributions of galaxies within haloes decreases the correlation function by up to 20 per cent for r<1 Mpc/h and increases it slightly at somewhat larger radii. Similar results apply to power spectra and redshift-space correlation functions. Models based on the Halo Occupation Distribution, which place galaxies spherically within haloes according to a mean radial profile, will therefore significantly underestimate the clustering on sub-Mpc scales. In addition, we find that halo assembly bias, in particular the dependence of clustering on halo shape, propagates to the clustering of galaxies. We predict that this aspect of assembly bias should be observable through the use of extensive group catalogues.

8 pages, 6 figures. Accepted for publication in MNRAS. Minor changes relative to v1. Note: this is an revised and considerably extended resubmission of http://arxiv.org/abs/1110.4888; please refer to the current version rather than the old one

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• Cosmic web anisotropy is the primary indicator of halo assembly bias
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• Five-percent measurements of the growth rate from simulation-based modelling of redshift-space clustering in BOSS LOWZ
• The halo model for cosmology: a pedagogical review
• Reconstructing the distribution of haloes and mock galaxies below the resolution limit in cosmological simulations
• Clues on void evolution III: Structure and dynamics in void shells
• The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias
• The nature of assembly bias - III. Observational properties
• Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters: Marginalizing over the Physics of Galaxy Formation
• Galactic conformity measured in semi-analytic models
• The galaxy correlation function as a constraint on galaxy formation physics
• Subhaloes gone Notts: Subhaloes as tracers of the dark matter halo shape
• Using galaxy pairs to investigate the three-point correlation function in the squeezed limit
• Testing the Impact of Satellite Anisotropy on Large and Small Scale Intrinsic Alignments using Hydrodynamical Simulations
• Anisotropic Halo Model
• The importance of the cosmic web and halo substructure for power spectra
• Mass accretion rates and multi-scale halo environment in cold and warm dark matter cosmologies
• The SRG/eROSITA All-Sky Survey: Exploring halo assembly bias with X-ray selected superclusters
• A Random Walk Model for Halo Triaxiality