Abstract
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.
Highlights
Halo models of the large scale structure of matter are very popular, as simple searches on the Internet show: for example, a Google search with the three words “halo model cosmology” produces4,680,000 results, and an ArXiv search for “halo model” yields “too many hits” and recommends a more specific search
The modern report on halo models by Cooray and Sheth [1] traces the appearance of these models to 1952, in a paper about the spatial distribution of galaxies written by Neyman and Scott [2], Galaxies 2013, 1 where they argue that it is “useful to think of the galaxy distribution as being made up of distinct clusters with a range of sizes.”
It seems inevitable to conclude that the presence of an intrinsic scale in cosmological N-body simulations, namely, the discreteness scale N −1/3, severely affects the type of mass distribution that is produced below that scale, to the extent that the smooth halos with a range of sizes about that scale that are commonly seen in these simulations are probably an artifact of insufficient resolution
Summary
Halo models of the large scale structure of matter are very popular, as simple searches on the Internet show: for example, a Google search with the three words “halo model cosmology” produces. Our main concern is to find out if halo models of the large scale structure are well justified, if smooth halos with a range of sizes are well justified by cosmological N-body simulations. Regarding this problem, we have to assess the spherical collapse and virialization model that is supposed to lead to the formation of halos. The large scale distribution of matter, whether made up by halos or not, displays definite features, namely, filaments and walls, which constitute the famous “cosmic web” structure This structure is reproduced by the adhesion model, which is worth studying. Some critical conclusions are presented and discussed
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