The Three Hundred Project: Correcting for the hydrostatic-equilibrium mass bias in X-ray and SZ surveys

Abstract

Accurate and precise measurements of masses of galaxy clusters are key to derive robust constraints on cosmological parameters. Rising evidence from observations, however, confirms that X-ray masses, obtained under the assumption of hydrostatic equilibrium, might be underestimated, as previously predicted by cosmological simulations. We analyse more than 300 simulated massive clusters, from 'The Three Hundred Project', and investigate the connection between mass bias and several diagnostics extracted from synthetic X-ray images of these simulated clusters. We find that the azimuthal scatter measured in 12 sectors of the X-ray flux maps is a statistically significant indication of the presence of an intrinsic (i.e. 3D) clumpy gas distribution. We verify that a robust correction to the hydrostatic mass bias can be inferred when estimates of the gas inhomogeneity from X-ray maps (such as the azimuthal scatter or the gas ellipticity) are combined with the asymptotic external slope of the gas density or pressure profiles, which can be respectively derived from X-ray and millimetric (Sunyaev-Zeldovich effect) observations. We also obtain that mass measurements based on either gas density and temperature or gas density and pressure result in similar distributions of the mass bias. In both cases, we provide corrections that help reduce both the dispersion and skewness of the mass bias distribution. These are effective even when irregular clusters are included leading to interesting implications for the modelling and correction of hydrostatic mass bias in cosmological analyses of current and future X-ray and SZ cluster surveys.

Measuring H0 using X-ray and SZ effect observations of dynamically relaxed galaxy clusters

“…As noted above, our fits are constrained almost entirely from data probing the radial range 0.1-1.0 500 , where such clumping is expected to be at a minimum from both simulations (e.g., Battaglia et al 2015;Planelles et al 2017) and observations (e.g., Simionescu et al 2011;Urban et al 2014;Eckert et al 2015). For these radii, simulations place the expected bias due to clumping at ∼ 3-5 per cent in R (Roncarelli et al 2013;Ansarifard et al 2020). Observational limits on the combined impact of clumping and turbulent density fluctuations in comparable regions of the Coma cluster are at the ∼ 4 ± 1 per cent level at scales of tens of kpc (Zhuravleva et al 2019); since Coma is a merging system, this suggests that clumping in relaxed clusters may be somewhat smaller than the predictions from simulations.…”

“…We adopt a uniform prior between −0.1 to 0.0 for HSE , a range comfortably including the predictions of hydrodynamical simulations specifically of massive, relaxed clusters at radii ∼ 2500 (Nagai et al 2007;Ansarifard et al 2020). The ratio of weak lensing to X-ray masses at the same radius for clusters satisfying the same relaxation criterion as our sample was measured to be wl−x = 0.96 ± 0.12, accounting for both statistical and lensing systematic uncertainties (Applegate et al 2016).…”

The Three Hundred Project: Substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters

“…The hydrodynamical clusters consist of dark matter and gas particles, and star particles of variable masses, typically with mstar ∼ 4 × 10 7 h −1 M , produced by the stochastic star-formation that is implemented by gadgetX (Tornatore et al 2007;Murante et al 2010;Rasia et al 2015). TheThreeHundred dataset is described in more extensive detail in Cui et al (2018), and has been used in previous studies to examine cluster density profiles (Mostoghiu et al 2019;Li et al 2020), environments (Wang et al 2018;Kuchner et al 2020), ram pressure (Arthur et al 2019), the hydrostatic equilibrium mass bias (Ansarifard et al 2020), backsplash galaxies (Haggar et al 2020), and the shapes and alignments of galaxies (Knebe et al 2020). Table 1.…”

The Cluster HEritage project withXMM-Newton: Mass Assembly and Thermodynamics at the Endpoint of structure formation

“…The theoretical picture is also uncertain. A significant upward revision of the total mass would imply that cluster baryon fractions were significantly lower than the universal value, at odds with expectations from numerical simulations (e.g., Planelles et al 2017;Ansarifard et al 2020). Similarly, while simulations predict some turbulence and non-thermal pressure support from gas motions generated by the hierarchical assembly process, they do not indicate that clusters are strongly out of equilibrium on average (e.g., Biffi et al 2016;Ansarifard et al 2020;Angelinelli et al 2020).…”