Constrained simulations and excursion sets: understanding the risks and benefits of `genetically modified' haloes

Abstract

Constrained realisations of Gaussian random fields are used in cosmology to design special initial conditions for numerical simulations. We review this approach and its application to density peaks providing several worked-out examples. We then critically discuss the recent proposal to use constrained realisations to modify the linear density field within and around the Lagrangian patches that form dark-matter haloes. The ambitious concept is to forge `genetically modified' haloes with some desired properties after the non-linear evolution. We demonstrate that the original implementation of this method is not exact but approximate because it tacitly assumes that protohaloes sample a set of random points with a fixed mean overdensity. We show that carrying out a full genetic modification is a formidable and daunting task requiring a mathematical understanding of what determines the biased locations of protohaloes in the linear density field. We discuss approximate solutions based on educated guesses regarding the nature of protohaloes. We illustrate how the excursion-set method can be adapted to predict the non-linear evolution of the modified patches and thus fine tune the constraints that are necessary to obtain preselected halo properties. This technique allows us to explore the freedom around the original algorithm for genetic modification. We find that the quantity which is most sensitive to changes is the halo mass-accretion rate at the mass scale on which the constraints are set. Finally we discuss constraints based on the protohalo angular momenta.

16 pages, 5 figures, accepted for publication in MNRAS

References in corpus (28)

• Ellipsoidal collapse and an improved model for the number and spatial distribution of dark matter haloes
• How Filaments are Woven into the Cosmic Web
• Ahf: Amiga's Halo Finder
• Halo Assembly Bias in Hierarchical Structure Formation
• The Excursion Set Theory of Halo Mass Functions, Halo Clustering, and Halo Growth
• Testing Tidal-Torque Theory: I. Spin Amplitude and Direction
• Evolution of the angular momentum of protogalaxies from tidal torques: Zel'dovich approximation
• Cosmic Shear from Galaxy Spins
• Testing Tidal-Torque Theory: II. Alignment of Inertia and Shear and the Characteristics of Proto-haloes
• Constraining Peaks in Gaussian Primordial Density Fields: an Application of the Hoffman-Ribak Method
• Enrichment of the ICM of galaxy clusters due to ram-pressure stripping
• Collapse Barriers and Halo Abundance: Testing the Excursion Set Ansatz
• Baryon acoustic signature in the clustering of density maxima
• One step beyond: The excursion set approach with correlated steps
• The Peaks Formalism and the Formation of Cold Dark Matter Haloes
• Genetically modified halos: towards controlled experiments in $\Lambda$CDM galaxy formation
• Ellipsoidal halo finders and implications for models of triaxial halo formation
• The spatial and velocity bias of linear density peaks and proto-haloes in the Lambda cold dark matter cosmology
• A Cosmological Kinetic Theory for the Evolution of Cold Dark Matter Halos with Substructure: Quasi-Linear Theory
• Velocity bias in the distribution of dark matter halos
• The formation of CDM haloes I: Collapse thresholds and the ellipsoidal collapse model
• The Dark Side of QSO Formation at High Redshifts
• Constrained Cosmological Simulations of Dark Matter Halos
• The formation of CDM haloes II: collapse time and tides
• The locations of halo formation and the peaks formalism
• Shear Fields and the Evolution of Galactic-Scale Density Peaks
• Effective Window Function for Lagrangian Halos
• Lagrangian Statistics of Dark Halos in a LCDM Cosmology

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• Large-Scale Galaxy Bias
• Quadratic genetic modifications: a streamlined route to cosmological simulations with controlled merger history
• The early growth of supermassive black holes in cosmological hydrodynamic simulations with constrained Gaussian realizations
• Growing the First Galaxies' Merger Trees
• Not all peaks are created equal: the early growth of Supermassive Black Holes