Universality of dark matter haloes shape over six decades in mass: insights from the Millennium XXL and SBARBINE simulations
Résumé
For the last 30 yr many observational and theoretical evidences have shown that galaxy clusters are not spherical objects, and that their shape is much better described by a triaxial geometry. With the advent of multiwavelength data of increasing quality, triaxial investigations of galaxy clusters is gathering a growing interest from the community, especially in the time of `precision cosmology'. In this work, we aim to provide the first statistically significant predictions in the unexplored mass range above 3 x 10(14) M(circle dot)h(-1), using haloes from two redshift snapshots (z = 0 and z = 1) of the Millennium XXL simulation. The size of this cosmological dark matter-only simulation (4.1 Gpc) allows the formation of a statistically significant number of massive cluster scale haloes (approximate to 500 with M \textgreater 2 x 10(15) M(circle dot)h(-1), and 780 000 with M \textgreater 10(14) M(circle dot)h(-1)). Besides, we aim to extend this investigation to lower masses in order to look for universal predictions across nearly six orders of magnitude in mass, from 10(10) to almost 10(16) M(circle dot)h(-1). For this purpose we use the SBARBINE simulations, allowing us to model haloes of masses starting from approximate to 10(10) M-circle dot h(-1). We use an elliptical overdensity method to select haloes and compute the shapes of the unimodal ones (approximately 50 per cent), while we discard the more unrelaxed. The minor to major and intermediate to major axis ratio distributions are found to be well described by simple universal functional forms that do not depend on cosmology or redshift. Our results extend the findings of Jing & Suto to a higher precision and a wider range of mass. This `recipe' is made available to the community in this paper and in a dedicated web page.
Domaines
Astrophysique [astro-ph]
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