The Cosmic Thermal History Probed by Sunyaev-Zeldovich Effect Tomography

TL;DR

This paper measures the evolution of the universe's thermal energy using Sunyaev-Zeldovich effect tomography, revealing a significant increase in electron temperature and energy density up to redshift 1, and providing new constraints on cosmic thermal history.

Contribution

It presents the first high-redshift measurements of the thermal Sunyaev-Zeldovich effect using cross-correlated sky maps and spectroscopic redshifts, constraining the evolution of the universe's thermal energy density.

Findings

Detected a threefold increase in electron temperature from z=1 to today.

Measured the build-up of 70% of present-day thermal energy density since z=1.

Estimated the mean Compton parameter y as 1.2×10⁻⁶, consistent with future spectral distortion tests.

Abstract

The cosmic thermal history, quantified by the evolution of the mean thermal energy density in the universe, is driven by the growth of structures as baryons get shock heated in collapsing dark matter halos. This process can be probed by redshift-dependent amplitudes of the thermal Sunyaev-Zeldovich (SZ) effect background. To do so, we cross-correlate eight sky intensity maps in the $\it{Planck}$ and Infrared Astronomical Satellite missions with two million spectroscopic redshift references in the Sloan Digital Sky Surveys. This delivers snapshot spectra for the far-infrared to microwave background light as a function of redshift up to $z\sim3$. We decompose them into the SZ and thermal dust components. Our SZ measurements directly constrain $\langle bP_{\rm e} \rangle$, the halo bias-weighted mean electron pressure, up to $z\sim 1$. This is the highest redshift achieved to date, with uncorrelated redshift bins thanks to the spectroscopic references. We detect a threefold increase in the density-weighted mean electron temperature $\bar{T}_{\rm{e}}$ from $7\times 10^5~{\rm K}$ at $z=1$ to $2\times 10^6~{\rm K}$ today. Over $z=1$-$0$, we witness the build-up of nearly $70\%$ of the present-day mean thermal energy density $\rho_{\rm{th}}$, with the corresponding density parameter $\Omega_{\rm th}$ reaching $1.5 \times10^{-8}$. We find the mass bias parameter of $\it{Planck}$'s universal pressure profile of $B=1.27$ (or $1-b=1/B=0.79$), consistent with the magnitude of non-thermal pressure in gas motion and turbulence from mass assembly. We estimate the redshift-integrated mean Compton parameter $y\sim1.2\times10^{-6}$, which will be tested by future spectral distortion experiments. More than half of which originates from the large-scale structure at $z<1$, which we detect directly.