Constraints on the Sunyaev-Zel'dovich signal from the Warm Hot Intergalactic Medium from WMAP and SPT data

TL;DR

This study investigates the contribution of the Warm Hot Intergalactic Medium to the CMB anisotropies using WMAP and SPT data, setting upper limits on its signal and constraining its physical properties.

Contribution

It provides the first constraints on the WHIM's Sunyaev-Zel'dovich signal using combined WMAP and SPT data, and links these constraints to the physical state of the diffuse gas.

Findings

Marginal evidence for WHIM contribution with A_WHIM=10-20 μK^2

Upper limit on WHIM contribution: A_WHIM < 43 μK^2 (95.4% C.L.)

Baryon fraction in the WHIM estimated between 0.43 and 0.47

Abstract

The fraction of ionized gas in the Warm Hot Intergalactic Medium induces temperature anisotropies on the Cosmic Microwave Background similar to those of clusters of galaxies. The Sunyaev-Zel'dovich anisotropies due to these low density, weakly non-linear, baryon filaments can not be distinguished from that of clusters using frequency information, but they can be separated since their angular scales are very different. To determine the relative contribution of the WHIM SZ signal to the radiation power spectrum of temperature anisotropies, we explore the parameter space of the concordance LCDM model using Monte Carlo Markov Chains and the Wilkinson Microwave Anisotropy Probe 7yr and South Pole Telescope data. We find marginal evidence of a contribution by diffuse gas, with amplitudes of A_WHIM=10-20 muK^2, but the results are also compatible with a null contribution from the WHIM, allowing to set an upper limit of A_WHIM < 43 muK^2 (95.4% C.L.). The signal produced by galaxy clusters remains at A_CL=4.5 muK^2, a value similar to what is obtained when no WHIM is included. From the measured WHIM amplitude we constrain the temperature-density phase diagram of the diffuse gas, and find it to be compatible with numerical simulations. The corresponding baryon fraction in the WHIM varies from 0.43 to 0.47, depending on model parameters. Planck data could set tighter constraints on the temperature-density relation.