Constraining cosmological parameters using the splashback radius of galaxy clusters

Constraining cosmological parameters using the splashback radius of galaxy clusters
Roan Haggar, Yuba Amoura, Charlie T. Mpetha, James E. Taylor, Kris Walker, Chris Power
arXiv:2406.17849v1 Announce Type: new
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.arXiv:2406.17849v1 Announce Type: new
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.