Dear Colleagues,

Following the standard cosmological bottom-up scenario, structure forms as consequence of gravitational instability of tiny perturbations imprinted on the matter distribution during an inflationary epoch. The resulting haloes, mostly made of dark matter, evolve through a sequence of collapse at very high redshift, followed by continuous accretion and repeated mergers with other haloes. The potential wells created by haloes is where baryons gather into galaxies; galaxy clusters, being the most recent and most massive virialized systems to assemble, sit at the vertex of this hierarchical pyramid.

Understanding the formation of dark matter haloes is therefore a crucial step for a proper characterization of the galaxy distribution within the cosmic web. The primary tools in this task are N-body simulations, while analytical approaches have also been demonstrated to be extremely useful to gain insight on the physical processes at work in the formation of these haloes.

Over the last few decades, it became clear that the clustering of galaxies, and the haloes they live in, are not only interesting scientific question per se, but can actually be exploited as a powerful cosmological probe.

Ongoing and future wide field survey have the potential to dramatically change our understanding of the Universe, shedding light on the nature of dark energy and testing gravity to an unprecedented accuracy level, but realizing their promise will require an accurate description of galaxy properties as a function of redshift, environment, halo mass and structural properties (fundamental to assess selection effects) in order to use the data for a full cosmological inspection.

The aim of this Special Issue of Galaxies is to give a broad and organic review, in this very special stage where models are being adapted to fully exploit forthcoming percent accuracy in clustering and lensing measurements, of the modeling of dark matter haloes and its interaction with cosmology.

The first part of this Special Issue of Galaxies will focus on reviewing recent results from numerical simulations, approximate methods and perturbation theory about the characterization of halo properties as a function of mass, redshift and local environment. We will discuss why haloes with different mass are characterized by a different bias parameter, with respect to the underlying matter density field, and how the bias varies for same mass systems as a function of particular halo properties.

The second part will focus on how galaxies populate haloes, and how galaxy formation changes halo properties with respect to the widely used collisionless N-body simulations. We will summarize the developments of cosmological hydrodynamical simulations, semi-analytical models and Halo Occupation Distribution techniques.

Dr. Emanuele Castorina
Dr. Carlo Giocoli
Dr. Pierluigi Monaco
Guest Editors

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• numerical simulation
• cosmology
• galaxy formation
• dark matter haloes
• halo bias