http://arxiv.org/abs/1312.4629
It is common practice to describe formal size and mass scales of dark matter haloes as spherical overdensities with respect to an evolving density threshold. Here, we critically investigate the evolutionary effects of several such commonly used definitions and compare them to the halo evolution within fixed physical scales as well as to the evolution of other intrinsic physical properties of dark matter haloes. It is shown that, in general, the traditional way of characterising sizes and masses of haloes dramatically overpredicts the degree of evolution in the last 10 Gyr, especially for low mass haloes. This pseudo-evolution is leading to the illusion of growth even though there are no major changes within fixed physical scales. Such formal size definitions also serve as proxies for the virialised region of a halo in the literature. In general, those spherical overdensity scales do not coincide with the virialised region. A physically more precise nomenclature would be to just characterise them by their very definition instead of calling such formal size and mass definitions ‘virial’. In general, we find a discrepancy between the evolution of the underlying physical structure of dark matter haloes seen in cosmological structure formation simulations and pseudo-evolving formal virial quantities. We question the importance of the role of formal virial quantities currently ubiquitously used in descriptions, models and relations that involve properties of dark matter structures. Concepts and relations based on pseudo-evolving formal virial quantities do not properly reflect the actual evolution of dark matter haloes and lead to an inaccurate picture of the physical evolution of our Universe.
Wed, 18 Dec 13
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