Why does the clustering of haloes depend on their formation history

Abstract

We discuss in the framework of the excursion set formalism a recent discovery from N-body simulations that the clustering of haloes of given mass depends on their formation history. We review why the standard implementation of this formalism is unable to explain such dependencies, and we show that this can, in principle, be rectified by implementing in full an ellipsoidal collapse model where collapse depends not only on the overdensity but also on the shape of the initial density field. We also present an alternative remedy for this deficiency, namely the inclusion of collapse barriers for pancakes and filaments, together with the assumption that formation history depends on when these barriers are crossed. We implement both these extensions in a generalised excursion set method, and run large Monte Carlo realisations to quantify the effects. Our results suggest that effects as large as those found in simulations can only arise in the excursion set formalism if the formation history of a halo does indeed depend on the size of its progenitor filaments and pancakes. We also present conditional distributions of progenitor pancakes and filaments for low-mass haloes identified at present epoch, and discuss a recent claim by Mo et.al. that most low-mass haloes were embedded in massive pancakes at $z\sim 2$.

11 pages, 8 figures, submitted to MNRAS

References in corpus (3)

• The spin and shape of dark matter haloes in the Millennium simulation of a LambdaCDM universe
• Halo assembly bias and its effects on galaxy clustering
• The Clustering of Massive Halos

Cited by in corpus (14)

• On Halo Formation Times and Assembly Bias
• The baryon fraction of LambdaCDM haloes
• Environmental Dependence of Dark Matter Halo Growth I: Halo Merger Rates
• Non-local Lagrangian bias
• Environmental dependence in the ellipsoidal collapse model
• Environmental Effects on Real-Space and Redshift-Space Galaxy Clustering
• Excursion Set Halo Mass Function and Bias in a Stochastic Barrier Model of Ellipsoidal Collapse
• Relating the structure of dark matter halos to their assembly and environment
• Close Pairs as Proxies for Galaxy Cluster Mergers
• Environmental Effects of Dark Matter Haloes: The Clustering-Substructure relation of Group-size Haloes
• Evaluating the origins of the secondary bias based on the correlation of halo properties with the linear density field
• Accurate halo mass functions from the simplest excursion set theory
• Excursion Sets with a "Perfect" Collapse Model
• The role of energy shear in the collapse of protohaloes