FLAMINGO: The thermal history of the Universe from tSZ effect cross-correlations and its dependencies on cosmology and baryon physics

Abstract

The cross-correlation between tracers of large-scale structure, such as galaxies or quasars, and the thermal Sunyaev-Zel'dovich (tSZ) signal yields a measure of the bias-weighted mean electron pressure, $⟨b_{\mathrm{h}}{P}_{\mathrm{e}}⟩$, where $b_{\mathrm{h}}$ is the halo bias and $P_{\mathrm{e}}$ is the electron pressure. With a model for the bias, one can derive the thermal history, $\mathrm{d}y/\mathrm{d}z$, where $y$ is the Compton parameter and $z$ is redshift. We explore how these quantities depend on redshift, cosmology, and the physics of galaxy formation using the FLAMINGO suite of cosmological hydrodynamical simulations, which spans a range of cosmological parameters and baryonic feedback implementations in volumes of up to $(2.8\text{Gpc}{)}^3$. We find that $⟨b_{\mathrm{h}}{P}_{\mathrm{e}}⟩$ depends steeply on $S_8\equiv {\sigma }_8\sqrt{{\Omega }_{\mathrm{m}}/0.3}$, with an effective scaling $⟨b_{\mathrm{h}}{P}_{\mathrm{e}}⟩\propto S_8^{\epsilon (z)}$, where the exponent $\epsilon (z)\approx 3$ over the redshift range $0.1\le z\le 1$. Compared with existing cross-correlation measurements using tracer samples from SDSS, BOSS, eBOSS, DES, and DESI cross-correlated with tSZ measurements from Planck, we find that models with a low-$S_8$ cosmology and strong feedback are preferred, with a joint fit yielding $S_8=0.72_{-0.03}^{+0.03}$ and a normalised group-mass halo baryon fraction $f_b(10^{13}{M}_{\odot },z=0.1)/({\Omega }_b/{\Omega }_m)=0.10_{-0.05}^{+0.09}$ . Contrary to most probes of feedback which sample smaller scales (e.g., X-ray measurements), we show that feedback boosts $⟨b_{\mathrm{h}}{P}_{\mathrm{e}}⟩$, thus providing a novel test of feedback models. Overall, our results show the thermal history provides a route to jointly constrain cosmological parameters and test models of galaxy formation.

Submitted to MNRAS. 22 pages, 15 figures