Virgo: an unlikely cluster of galaxies because of its environment. (arXiv:1904.07253v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Sorce_J/0/1/0/all/0/1">Jenny G. Sorce</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blaizot_J/0/1/0/all/0/1">Jérémy Blaizot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dubois_Y/0/1/0/all/0/1">Yohan Dubois</a>
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.
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.
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