Halo concentration, galaxy red fraction, and gas properties of optically defined merging clusters

Abstract

We present multi-wavelength studies of optically-defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers, which is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple-peaks and single clusters with single-peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of the merging clusters is categorized into major mergers. The average halo concentration for the merging clusters is ∼ 70% smaller than that of the single-peak clusters, which agrees well with predictions of numerical simulations. The spatial distribution of subhalos is less centrally concentrated than the mass distribution of the main halo. The fractions of red galaxies in the merging clusters are not higher than those of the single-peak clusters. We find a signature of the merger boost of the ICM from stacked Planck Sunyaev-Zeldovich effect and ROSAT X-ray luminosity, but not in optical richness. The stacked X-ray surface brightness distribution, aligned with the main-subhalo pairs of low redshift and massive clusters, shows that the central gas core is elongated along the merger axis and overall gas distribution is misaligned by ∼ 60 deg. The homogeneous, unbiased sample of cluster mergers and multi-wavelength follow-up studies provide a unique opportunity to make a complete picture of merger physics over the whole process.

Weak-lensing Analysis of X-Ray-selected XXL Galaxy Groups and Clusters with Subaru HSC Data

“…The level of contamination by cluster members depends on and increases with the cluster mass or richness (Medezinski et al 2018b). For our sample that is dominated by low-mass clusters and groups, we thus expect a less significant degree of dilution of the weak-lensing signal compared to previous HSC cluster weak-lensing studies (e.g., Medezinski et al 2018b,a;Miyaoka et al 2018;Miyatake et al 2019;Okabe et al 2019).…”

“…We use this subsample for our testing purposes. We note that it is appropriate to assume a log-uniform prior, instead of a uniform prior, for a positive-definite quantity, especially when the quantity spans a wide dynamic range (e.g., Sereno & Covone 2013;Umetsu et al 2014Umetsu et al , 2016Umetsu et al , 2018Okabe et al 2019). Such a treatment is also self-consistent with our scaling relation analysis, where we work with logarithmic quantities, log M ∆ and log c 200 (Section 5).…”

“…In our ensemble analysis of the XXL sample, we will include a 1% systematic uncertainty on the residual multiplicative bias (see Section 4.2; Mandelbaum et al 2018b;Hikage et al 2019). We also conservatively correct for additive residual shear bias by subtracting off the weighted mean offset from Equation (4) (see Mandelbaum et al 2018a;Miyaoka et al 2018;Okabe et al 2019). The shear responsivity R(R i ) is calculated as (see also Mandelbaum et al.…”

Discovery of a supercluster in the eROSITA Final Equatorial Depth Survey: X-ray properties, radio halo, and double relics

“…Radio relics are elongated (∼Mpc), steep-spectrum (α −1) synchrotron sources that sit preferentially at the edges of galaxy clusters (e.g., Enßlin et al 1998;van Weeren et al 2010van Weeren et al , 2019Brunetti & Jones 2014;Pearce et al 2017). There is a consensus that radio relics are produced by large shock waves but many aspects, including the cause for the apparently high particle acceleration efficiency, remain unclear (e.g., Botteon et al 2016bBotteon et al , 2020bvan Weeren et al 2016b;Hoang et al 2017Hoang et al , 2018Okabe et al 2019Okabe et al , 2021Brüggen & Vazza 2020). Another type of extended synchrotron radio source, namely halos, is often found in the central region of galaxy clusters.…”

Cluster–galaxy weak lensing

“…In general, it is appropriate to assume a log-uniform prior, instead of a uniform prior, for a positivedefinite quantity such as M 200c and c 200c , especially when the quantity spans a wide dynamic range(Umetsu et al 2014(Umetsu et al , 2020Okabe et al 2019). Such a treatment is also self-consistent with mass-scaling relation analysis, where one often works with logarithmic quantities (e.g., ln M D ; ln c D ).…”