paper

Virgo: an unlikely cluster of galaxies because of its environment

arXiv:1904.07253 · doi:10.1093/mnras/stz1080

Abstract

Galaxy clusters constitute powerful cosmological probes thanks to comparisons between observed and simulated clusters. As such Virgo constitutes a formidable source for detailed observations facilitated by its proximity. However, the diversity of clusters complicates the comparisons on a one-to-one basis. Simulated clusters must be carefully selected, a daunting task since most properties are unknown. Alternatively, lookalikes produced in the proper large scale environment can be used. Additionally, their statistical study give access to the mean properties of the observed cluster including its most probable history as well as its deviation from an average cluster. This paper presents such a statistical study with 200 Virgo-like and 400+ cluster-size random dark matter halos. Only 18%(0.5%) of these random halos comply within 3(2)-sigma with the mean values (radius, velocity dispersion, number of substructures, spin, velocity, concentration, center of mass offset with respect to the spherical center) of Virgo halos at z=0 and abide by a similar merging history up to redshift 4. None are within 1-sigma because of environmentally induced properties (number of substructures and velocity). For further comparisons, random halos are selected to reproduce the mass distribution of the lookalikes to cancel mass bias effects. Redshift 1 appears then as a turning point: random to Virgo-like property ratios are alternatively smaller/larger than 1. This highlights the importance of studying clusters within their proper large scale environment: simulated galaxy population, grandly affected by the cluster history, can then be compared with the observed one in details. Direct lookalikes simplify grandly the challenge.

Accepted for publication in MNRAS, 12 pages, 7 figures, 5 tables

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