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High-resolution spectroscopy in soft X-rays will open a new window to map multiphase gas in galaxy clusters and probe physics of the intracluster medium (ICM), including chemical enrichment histories, circulation of matter and energy during large-scale structure evolution, stellar and black hole feedback, halo virialization, and gas mixing processes. An eV-level spectral resolution, large field of view, and effective area are essential to separate cluster emissions from the Galactic foreground and efficiently map the cluster outskirts. Several mission concepts that meet these criteria have been proposed recently, e.g. LEM, HUBS, and Super DIOS. This theoretical study explores what information on ICM physics could be recovered with such missions and the associated challenges. We emphasize the need for a comprehensive comparison between simulations and observations to interpret the high-resolution spectroscopic observations correctly. Using Line Emission Mapper (LEM) characteristics as an example, we demonstrate that it enables the use of soft X-ray emission lines (e.g. O  vii / viii and Fe-L complex) from the cluster outskirts to measure the thermodynamic, chemical, and kinematic properties of the gas up to r 200 and beyond. By generating mock observations with full backgrounds, analysing their images/spectra with observational approaches, and comparing the recovered characteristics with true ones from simulations, we develop six key science drivers for future missions, including the exploration of multiphase gas in galaxy clusters (e.g. temperature fluctuations, phase-space distributions), metallicity, ICM gas bulk motions and turbulence power spectra, ICM-cosmic filament interactions, and advances for cluster cosmology. [ABSTRACT FROM AUTHOR]

We study the impact of resonantly scattered X-ray line emission on the observability of the hot circumgalactic medium (CGM) of galaxies. We apply a Monte Carlo radiative transfer post-processing analysis to the high-resolution TNG50 cosmological magnetohydrodynamical galaxy formation simulation. This allows us to model the resonant scattering of  O  vii (r) X-ray photons within the complex, multiphase, multiscale CGM. The resonant transition of the O  vii He-like triplet is one of the brightest, and most promising, X-ray emission lines for detecting the hot CGM and measuring its physical properties. We focus on galaxies with stellar masses |$10.0\lt \log {(M_\star /\rm {M_\odot })}\lt 11.0$| at z ≃ 0. After constructing a model for  O  vii (r) emission from the central galaxy, as well as from CGM gas, we forward model these intrinsic photons to derive observable surface brightness maps. We find that scattering significantly boosts the observable  O  vii (r) surface brightness of the extended and diffuse CGM. This enhancement can be large – an order of magnitude on average at a distance of 200 projected kpc for high-mass M ⋆ = 1010.7 M⊙ galaxies. The enhancement is larger for lower mass galaxies and can even reach a factor of 100, across the extended CGM. Galaxies with higher star formation rates, AGN luminosities, and central  O  vii (r) luminosities all have larger scattering enhancements, at fixed stellar mass. Our results suggest that next-generation X-ray spectroscopic missions, including XRISM, LEM, ATHENA, and HUBS – which aim to detect the hot CGM in emission – could specifically target haloes with significant enhancements due to resonant scattering. [ABSTRACT FROM AUTHOR]

We present a Chandra study of surface brightness fluctuations in the diffuse intracluster medium of the Perseus Cluster. Our study utilizes deep, archival imaging of the cluster core as well as a new mosaic of 29 short |$\, 5\,$| -ks observations extending in eight different directions out to radii of |$r_{500} \sim 2.2\, r_{2500}$|⁠. Under the assumption that the distribution of densities at a given radius is log-normally distributed, two important quantities can be derived from the width of the log-normal density distribution on a given spatial scale: the density bias, that is equal to the square root of the clumping factor C ; and the one-component turbulent velocity, v k ,1D. We forward-model all contributions to the measured surface brightness, including astrophysical and particle background components, and account for the Poisson nature of the measured signal. Measuring the distribution of surface brightness fluctuations in 1 arcmin2 regions, spanning the radial range |$0.3\rm {-}2.2\, r_{2500}$| (⁠|$7.8\rm {-}57.3\,$|  arcmin), we find a small to moderate average density bias of around |$3{{\ \rm per\ cent}}$| at radii below |$1.6\, r_{2500}$|⁠. We also infer an average turbulent velocity at these radii of V 1D < 400 km s−1. Direct confirmation of our results on turbulent velocities inferred from surface brightness fluctuations should be possible using the X-ray calorimeter spectrometers to be flown aboard the XRISM and Athena observatories. [ABSTRACT FROM AUTHOR]

When a subcluster merges with a larger galaxy cluster, a bow shock is driven ahead of the subcluster. At a later merger stage, this bow shock separates from the subcluster, becoming a 'runaway' shock that propagates down the steep density gradient through the cluster outskirts and approximately maintains its strength and the Mach number. Such shocks are plausible candidates for producing radio relics in the periphery of clusters. We argue that, during the same merger stage, a secondary shock is formed much closer to the main cluster centre. A close analogue of this structure is known in the usual hydrodynamics as N -waves, where the trailing part of the ' N ' is the result of the non-linear evolution of a shock. In merging clusters, spherical geometry and stratification could further promote its development. Both the primary and the secondary shocks are the natural outcome of a single merger event and often both components of the pair should be present. However, in the radio band, the leading shock could be more prominent, while the trailing shock might conversely be more easily seen in X-rays. The latter argument implies that for some of the (trailing) shocks found in X-ray data, it might be difficult to identify their 'partner' leading shocks or the merging subclusters, which are farther away from the cluster centre. We argue that the Coma cluster and A2744 could be two examples in a post-merger state with such well-separated shock pairs. [ABSTRACT FROM AUTHOR]