21CMMC with a 3D light-cone: the impact of the co-evolution approximation on the astrophysics of reionisation and cosmic dawn

TL;DR

This paper extends 21CMMC to analyze 3D light-cones of the 21cm signal, enabling more realistic parameter estimation for upcoming observations and assessing biases from the co-evolution approximation.

Contribution

It introduces a light-cone version of 21CMMC for direct parameter estimation on 3D data, bridging the gap between theory and tomographic observations.

Findings

Ignoring light-cone effects generally does not bias parameters significantly.

Significant biases can occur with rapid signal evolution and idealized data conditions.

Underestimation of uncertainties is common when neglecting light-cone effects.

Abstract

We extend 21CMMC, a Monte Carlo Markov Chain sampler of 3D reionisation simulations, to perform parameter estimation directly on 3D light-cones of the cosmic 21cm signal. This brings theoretical analysis closer to the tomographic 21-cm observations achievable with next generation interferometers like HERA and the SKA. Parameter recovery can therefore account for modes which evolve with redshift/frequency. Additionally, simulated data can be more easily corrupted to resemble real data. Using the light-cone version of 21CMMC, we quantify the biases in the recovered astrophysical parameters if we use the 21cm power spectrum from the co-evolution approximation to fit a 3D light-cone mock observation. While ignoring the light-cone effect under most assumptions will not significantly bias the recovered astrophysical parameters, it can lead to an underestimation of the associated uncertainty. However significant biases ($\sim$few -- 10 $\sigma$) can occur if the 21cm signal evolves rapidly (i.e. the epochs of reionisation and heating overlap significantly) and: (i) foreground removal is very efficient, allowing large physical scales ($k\lesssim0.1$~Mpc$^{-1}$) to be used in the analysis or (ii) theoretical modelling is accurate to within $\sim10$ per cent in the power spectrum amplitude.