An analysis of galaxy cluster mis-centring using cosmological hydrodynamic simulations. (arXiv:1912.06663v1 [astro-ph.CO])

An analysis of galaxy cluster mis-centring using cosmological hydrodynamic simulations. (arXiv:1912.06663v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yan_Z/0/1/0/all/0/1">Z. Yan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Raza_N/0/1/0/all/0/1">N. Raza</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Waerbeke_L/0/1/0/all/0/1">L. Van Waerbeke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mead_A/0/1/0/all/0/1">A. J. Mead</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCarthy_I/0/1/0/all/0/1">I. G. McCarthy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Troester_T/0/1/0/all/0/1">T. Troester</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hinshaw_G/0/1/0/all/0/1">G. Hinshaw</a>

The choice of which position to assign as the centre of a galaxy cluster can
have a significant impact on the inferred physical properties. Centre
definitions based on the galactic or gas component of the clusters are easier
to measure, but invariably introduce biases due to mis-centring. Using data
from the BAHAMAS cosmological hydrodynamic simulations we study this bias in
both two and three dimensions for 2000 clusters over the $10^{13} – 10^{15}
~mathrm{M_{odot}}$ mass range. We quantify and model the offset distributions
between observationally-motivated centres and the `true’ centre of the cluster,
which is taken to be the most gravitationally bound particle measured in the
simulation. We fit the cumulative distribution function of offsets with 6
different analytical models and find that a combination of an exponential
distribution and a Gamma distribution fit well with most of the centroid
definitions. The galaxy-based centres can be seen to be divided into a
mis-centred group and a well-centred group, with the well-centred group making
up about $60%$ of all the clusters. Gas-based centres are not as clearly
divided into two groups, but are overall less scattered than galaxy-based
centres. We also find a cluster-mass dependence of the offset distribution of
gas-based centres, with generally larger offsets for smaller mass clusters. We
then measure cluster density profiles centred at each choice of the centres and
fit them with empirical models. Stacked, mis-centred density profiles fit to
the Navarro-Frenk-White dark-matter profile and Komatsu-Seljak gas profile show
that recovered shape and size parameters can significantly deviate from the
true values. For the galaxy-based centres, this can lead to cluster masses
being underestimated by up to 10 per cent.

The choice of which position to assign as the centre of a galaxy cluster can
have a significant impact on the inferred physical properties. Centre
definitions based on the galactic or gas component of the clusters are easier
to measure, but invariably introduce biases due to mis-centring. Using data
from the BAHAMAS cosmological hydrodynamic simulations we study this bias in
both two and three dimensions for 2000 clusters over the $10^{13} – 10^{15}
~mathrm{M_{odot}}$ mass range. We quantify and model the offset distributions
between observationally-motivated centres and the `true’ centre of the cluster,
which is taken to be the most gravitationally bound particle measured in the
simulation. We fit the cumulative distribution function of offsets with 6
different analytical models and find that a combination of an exponential
distribution and a Gamma distribution fit well with most of the centroid
definitions. The galaxy-based centres can be seen to be divided into a
mis-centred group and a well-centred group, with the well-centred group making
up about $60%$ of all the clusters. Gas-based centres are not as clearly
divided into two groups, but are overall less scattered than galaxy-based
centres. We also find a cluster-mass dependence of the offset distribution of
gas-based centres, with generally larger offsets for smaller mass clusters. We
then measure cluster density profiles centred at each choice of the centres and
fit them with empirical models. Stacked, mis-centred density profiles fit to
the Navarro-Frenk-White dark-matter profile and Komatsu-Seljak gas profile show
that recovered shape and size parameters can significantly deviate from the
true values. For the galaxy-based centres, this can lead to cluster masses
being underestimated by up to 10 per cent.

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