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arXiv · 2406.17849

Constraining cosmological parameters using the splashback radius of galaxy clusters

Roan Haggar·Yuba Amoura·Charlie T. Mpetha·James E. Taylor·Kris Walker·Chris Power
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Abstract

Cosmological parameters such as $\Omega_{\rm{M}}$ and $\sigma_{8}$ can be measured indirectly using various methods, including galaxy cluster abundance and cosmic shear. These measurements constrain the composite parameter $S_{8}$, leading to degeneracy between $\Omega_{\rm{M}}$ and $\sigma_{8}$. However, some structural properties of galaxy clusters also correlate with cosmological parameters, due to their dependence on a cluster's accretion history. In this work, we focus on the splashback radius, an observable cluster feature that represents a boundary between a cluster and the surrounding Universe. Using a suite of cosmological simulations with a range of values for $\Omega_{\rm{M}}$ and $\sigma_{8}$, we show that the position of the splashback radius around cluster-mass halos is greater in cosmologies with smaller values of $\Omega_{\rm{M}}$ or larger values of $\sigma_{8}$. This variation breaks the degeneracy between $\Omega_{\rm{M}}$ and $\sigma_{8}$ that comes from measurements of the $S_{8}$ parameter. We also show that this variation is, in principle, measurable in observations. As the splashback radius can be determined from the same weak lensing analysis already used to estimate $S_{8}$, this new approach can tighten low-redshift constraints on cosmological parameters, either using existing data, or using upcoming data such as that from Euclid and LSST.

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Roan Haggar, Yuba Amoura, Charlie T. Mpetha, James E. Taylor, Kris Walker, Chris Power. 2024-06-25. Constraining cosmological parameters using the splashback radius of galaxy clusters. https://arxiv.org/abs/2406.17849

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