The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space study

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Mesinger, Andrei, McQuinn, Matthew, Spergel, David N.
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Papers; South Pole; South pole
• Online Access: http://mnras.oxfordjournals.org/cgi/content/short/422/2/1403; https://doi.org/10.1111/j.1365-2966.2012.20713.x

Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev–Zel’dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time, with projected 1 μ K2-level sensitivity to the dimensionless kSZ power spectrum around a multipole of l = 3000, [Δ l 3000 ]2. Indeed, recent SPT measurements place a bound of [Δ l 3000 ]2 < 2.8 μ K2 at 95 per cent confidence level, which degrades to [Δ l 3000 ]2 < 6 μ K2 if a significant correlation between the thermal Sunyaev–Zel’dovich (tSZ) effect and the cosmic infrared background (CIB) is allowed. To interpret these and upcoming observations, we compute the kSZ signal from a suite of ≈100 reionization models using the publicly available code <scp>21cmfast</scp>. Our physically motivated reionization models are parametrized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of haloes capable of hosting stars, and the ionizing photon mean free path – a parametrization motivated by previous theoretical studies of reionization. We predict the contribution of patchy reionization to the l = 3000 kSZ power to be <f> </f> 1.5–3.5 μ K2. Therefore, even when adopting the lowest estimate in the literature for the post-reionization signal of <f> </f>, none of our models are consistent with the aggressive 2σ SPT bound that does not include correlations. This implies the following: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g. very high energy X-rays or exotic particles contributed significantly and/or (ii) that there is a significant correlation between the CIB and the tSZ. The later is perhaps not surprising, as massive haloes should host both hot gas and star-forming galaxies. ...