The Sunyaev-Zeldovich effect in superclusters of galaxies using gasdynamical simulations: the case of Corona Borealis

TL;DR

This study uses gasdynamical simulations to analyze the Sunyaev-Zel'dovich effect in superclusters, specifically the Corona Borealis Supercluster, and assesses the likelihood of various gas components causing observed CMB temperature decrements.

Contribution

It provides the first detailed simulation-based analysis of SZ effects in superclusters, evaluating the contributions of WHIM and galaxy groups to observed signals.

Findings

WHIM produces a much smaller SZ effect than observed.

Small clusters and galaxy groups cannot fully explain the SZ signal.

Probability that WHIM causes the observed SZ effect is less than 1%.

Abstract

[Abridged] We study the thermal and kinetic Sunyaev-Zel'dovich (SZ) effect associated with superclusters of galaxies using the MareNostrum Universe SPH simulation. We consider superclusters similar to the Corona Borealis Supercluster (CrB-SC). This paper is motivated by the detection at 33GHz of a strong temperature decrement in the CMB towards the core of this supercluster. Multifrequency observations with VSA and MITO suggest the existence of a thermal SZ effect component in the spectrum of this cold spot, which would account for roughly 25% of the total observed decrement. We identify nine regions containing superclusters similar to CrB-SC, obtain the associated SZ maps and calculate the probability of finding such SZ signals arising from hot gas within the supercluster. Our results show that WHIM produces a thermal SZ effect much smaller than the observed value. Neither can summing the contribution of small clusters and galaxy groups in the region explain the amplitude of the SZ signal. When we take into account the actual posterior distribution from the observations, the probability that WHIM can cause a thermal SZ signal like the one observed is <1%, rising up to a 3.2% when the contribution of small clusters and galaxy groups is included. If the simulations provide a suitable description of the gas physics, then we conclude that the thermal SZ component of the CrB spot most probably arises from an unknown galaxy cluster along the line of sight. The simulations also show that the kinetic SZ signal associated with the supercluster cannot provide an explanation for the remaining 75% of the observed cold spot in CrB.