Abstract
Abstract Galaxy cluster outskirts mark the transition region from the mildly non-linear cosmic web to the highly non-linear, virialised, cluster interior. It is in this transition region that the intra-cluster medium (ICM) begins to influence the properties of accreting galaxies and groups, as ram pressure impacts a galaxy’s cold gas content and subsequent star formation rate. Conversely, the thermodynamical properties of the ICM in this transition region should also feel the influence of accreting substructure (i.e. galaxies and groups), whose passage can drive shocks. In this paper, we use a suite of cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn from the nIFTy comparison project, to study how the dynamics of substructure accreted from the cosmic web influences the thermodynamical properties of the ICM in the cluster’s outskirts. We demonstrate how features evident in radial profiles of the ICM (e.g. gas density and temperature) can be linked to strong shocks, transient and short-lived in nature, driven by the passage of substructure. The range of astrophysical codes and galaxy formation models in our comparison are broadly consistent in their predictions (e.g. agreeing when and where shocks occur, but differing in how strong shocks will be); this is as we would expect of a process driven by large-scale gravitational dynamics and strong, inefficently radiating, shocks. This suggests that mapping such shock structures in the ICM in a cluster’s outskirts (via e.g. radio synchrotron emission) could provide a complementary measure of its recent merger and accretion history.
Highlights
Galaxy clusters are the most massive virialized objects in the Universe, and are widely used as a powerful testbed for our theories of dark matter, dark energy, and galaxy formation and evolution, as well as cosmological parameter estimation (e.g. Kravtsov & BorganiC 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society2012; Mantz et al 2014, 2016; Sartoris et al 2016)
We focus on radial profiles of gas density, temperature, and radial velocity in the regime 0.3 ≤ R/R200 3, and investigate in detail the relationship between structures evident in these profiles, which we interpret as arising from shocks, and the orbital motions of substructures (Section 3.2) and accretion from the cosmic web (Section 3.3)
We have used a suite of cosmological hydrodynamical zoom simulations of a single galaxy cluster, run with a range of astrophysical codes and galaxy formation models as part of the NIFTY comparison project, to study how the thermodynamical properties of the intracluster medium (ICM) in a galaxy cluster’s outskirts (0.3 ≤ R/R200 3) at z = 0 are influenced by the accretion of substructure from the cosmic web
Summary
Galaxy clusters are the most massive virialized objects in the Universe, and are widely used as a powerful testbed for our theories of dark matter, dark energy, and galaxy formation and evolution, as well as cosmological parameter estimation Keshet et al 2003; Keshet, Waxman & Loeb 2004; Zandanel, Pfrommer & Prada 2014) to radio continuum emission in the form of synchrotron radiation as electrons spiral along magnetic fields (Hoeft et al 2008; Vazza, Brunetti & Gheller 2009) Both observations and simulations show trends between a cluster’s merging and mass accretion history – which, observationally, are inferred from estimates of its dynamical state – and properties of its ICM, such as gas ellipticity
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