Constraints on the temperature of the intergalactic medium at z = 8.4 with 21-cm observations

Abstract

We compute robust lower limits on the spin temperature, TS, of the z = 8.4 intergalactic medium (IGM), implied by the upper limits on the 21-cm power spectrum recently measured by PAPER-64. Unlike previous studies which used a single epoch of reionization (EoR) model, our approach samples a large parameter space of EoR models: the dominant uncertainty when estimating constraints on TS. Allowing TS to be a free parameter and marginalizing over EoR parameters in our Markov ChainMonte Carlo code 21CMMC, we infer TS ≥ 3 K (corresponding approximately to 1σ) for a mean IGM neutral fraction of xHI ≳ 0.1. We further improve on these limits by folding-in additional EoR constraints based on: (i) the ..