Sunyaev-Zel'dovich clusters in Millennium Gas simulations

TL;DR

This study uses Millennium Gas simulations to analyze the Sunyaev-Zel'dovich effect in galaxy clusters, confirming the tight Y_{500}-M_{500} relation's insensitivity to gas physics and its evolution, with implications for observational bias and cluster physics.

Contribution

First comprehensive analysis of SZ cluster properties across models with different gas physics using large simulations, confirming the relation's stability and agreement with recent observational data.

Findings

Y_{500}-M_{500} relation has very little scatter (~0.04) and is insensitive to gas physics.

Scaling relations agree with recent Planck and XMM-Newton data.

Projection effects do not bias the integrated SZ signal, but increase scatter in pre-heating models.

Abstract

We have exploited the large-volume Millennium Gas cosmological N-body hydrodynamics simulations to study the SZ cluster population at low and high redshift, for three models with varying gas physics. We confirm previous results using smaller samples that the intrinsic (spherical) Y_{500}-M_{500} relation has very little scatter (sigma_{log_{10}Y}~0.04), is insensitive to cluster gas physics and evolves to redshift one in accord with self-similar expectations. Our pre-heating and feedback models predict scaling relations that are in excellent agreement with the recent analysis from combined Planck and XMM-Newton data by the Planck Collaboration. This agreement is largely preserved when r_{500} and M_{500} are derived using the hydrostatic mass proxy, Y_{X,500}, albeit with significantly reduced scatter (sigma_{log_{10}Y}~0.02), a result that is due to the tight correlation between Y_{500} and Y_{X,500}. Interestingly, this assumption also hides any bias in the relation due to dynamical activity. We also assess the importance of projection effects from large-scale structure along the line-of-sight, by extracting cluster Y_{500} values from fifty simulated 5x5 square degree sky maps. Once the (model-dependent) mean signal is subtracted from the maps we find that the integrated SZ signal is unbiased with respect to the underlying clusters, although the scatter in the (cylindrical) Y_{500}-M_{500} relation increases in the pre-heating case, where a significant amount of energy was injected into the intergalactic medium at high redshift. Finally, we study the hot gas pressure profiles to investigate the origin of the SZ signal and find that the largest contribution comes from radii close to r_{500} in all cases. The profiles themselves are well described by generalised Navarro, Frenk & White profiles but there is significant cluster-to-cluster scatter.