Relativistic SZ temperatures and hydrostatic mass bias for massive clusters in the FLAMINGO simulations

Abstract

The relativistic Sunyaev-Zel'dovich (SZ) effect can be used to measure intracluster gas temperatures independently of X-ray spectroscopy. Here, we use the large-volume FLAMINGO simulation suite to determine whether SZ $y$-weighted temperatures lead to more accurate hydrostatic mass estimates in massive ($M_{500c}>7.5\times 10^{14}{\mathrm{M}}_{\odot }$) clusters than when using X-ray spectroscopic-like temperatures. We find this to be the case, on average. The median bias in the SZ mass at redshift zero is $⟨b⟩\equiv 1-⟨M_{500c,\mathrm{hse}}/M_{500c,\mathrm{true}}⟩=-0.05\pm 0.01$, over 4 times smaller in magnitude than the X-ray spectroscopic-like case, $⟨b⟩=0.22\pm 0.01$. However, the scatter in the SZ bias, ${\sigma }_b\approx 0.2$, is around 40 per cent larger than for the X-ray case. We show that this difference is strongly affected by clusters with large pressure fluctuations, as expected from shocks in ongoing mergers. Selecting the clusters with the best-fitting generalized NFW pressure profiles, the median SZ bias almost vanishes, $⟨b⟩=-0.009\pm 0.005$, and the scatter is halved to ${\sigma }_b\approx 0.1$. We study the origin of the SZ/X-ray difference and find that, at $R_{500c}$ and in the outskirts, SZ weighted gas better reflects the hot, hydrostatic atmosphere than the X-ray weighted gas. The SZ/X-ray temperature ratio increases with radius, a result we find to be insensitive to variations in baryonic physics, cosmology and numerical resolution.

19 pages, 22 figures, submitted to MNRAS. Comments welcome