The Cosmic Thermal History Probed by Sunyaev–Zeldovich Effect Tomography

Abstract

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 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 ∼ 3. We decompose them into the SZ and thermal dust components. Our SZ measurements directly constrain 〈 bP e 〉 , the halo bias-weighted mean electron pressure, up to z ∼ 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 T ¯ e from 7 × 105 K at z = 1 to 2 × 106 K today. Over z = 1–0, we witness the build-up of nearly 70% of the present-day mean thermal energy density ρ th, with the corresponding density parameter Ωth reaching 1.5 × 10−8. We find the mass bias parameter of Planck's universal pressure profile of B = 1.27 (or 1 − b = 1/B = 0.79), consistent with the magnitude of nonthermal pressure in gas motion and turbulence from mass assembly. We estimate the redshift-integrated mean Compton parameter y ∼ 1.2 × 10−6, which will be tested by future spectral distortion experiments. More than half originates from the large-scale structure at z < 1, which we detect directly.