Volume 628, August 2019
|Number of page(s)||38|
|Section||Cosmology (including clusters of galaxies)|
|Published online||06 August 2019|
Toward a characterization of X-ray galaxy clusters for cosmology
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
2 Department of Physics, University of Helsinki, PO Box 64 00014 Helsinki, Finland
3 Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
4 Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Accepted: 21 June 2019
Context. In the framework of the hierarchical model the intra-cluster medium properties of galaxy clusters are tightly linked to structure formation, which makes X-ray surveys well suited for cosmological studies. To constrain cosmological parameters accurately by use of galaxy clusters in current and future X-ray surveys, a better understanding of selection effects related to the detection method of clusters is needed.
Aims. We aim at a better understanding of the morphology of galaxy clusters to include corrections between the different core types and covariances with X-ray luminosities in selection functions. In particular, we stress the morphological deviations between a newly described surface brightness profile characterization and a commonly used single β-model.
Methods. We investigated a novel approach to describe surface brightness profiles, where the excess cool-core emission in the centers of the galaxy clusters is modeled using wavelet decomposition. Morphological parameters and the residuals were compared to classical single β-models, fitted to the overall surface brightness profiles.
Results. Using single β-models to describe the ensemble of overall surface brightness profiles leads on average to a non-zero bias (0.032 ± 0.003) in the outer part of the clusters, that is an approximate 3% systematic difference in the surface brightness at large radii. Furthermore, β-models show a general trend toward underestimating the flux in the outskirts for smaller core radii. Fixing the β parameter to 2/3 doubles the bias and increases the residuals from a single β-model up to more than 40%. Modeling the core region in the fitting procedure reduces the impact of these two effects significantly. In addition, we find a positive scaling between shape parameters and temperature, as well as a negative correlation of approximately −0.4 between extent and luminosity.
Conclusion. We demonstrate the caveats in modeling galaxy clusters with single β-models and recommend using them with caution, especially when the systematics are not taken into account. Our non-parametric analysis of the self-similar scaled emission measure profiles indicates no systematic core-type differences of median profiles in the galaxy cluster outskirts.
Key words: X-rays: galaxies: clusters / galaxies: clusters: general / cosmology: observations
© F. Käfer et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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