The 21-cm signature of the first stars during the Lyman-Werner feedback era

TL;DR

This paper models the joint evolution of X-ray and Lyman-Werner backgrounds during the first stars era, revealing delayed heating and promising 21-cm fluctuation signals detectable with upcoming instruments.

Contribution

It introduces a semi-numerical hybrid method that includes the effects of streaming velocities and Lyman-Werner feedback on early star formation and 21-cm signals.

Findings

Lyman-Werner feedback delays X-ray heating by Δz ~ 2.

Large-scale 21-cm fluctuations are detectable at z ~ 18-23.

Predicted signal-to-noise ratio of 3-4 at z ~ 18.

Abstract

The formation of the first stars is an exciting frontier area in astronomy. Early redshifts z ~ 20 have become observationally promising as a result of a recently recognized effect of a supersonic relative velocity between the dark matter and gas. This effect produces prominent structure on 100 comoving Mpc scales, which makes it much more feasible to detect 21-cm fluctuations from the epoch of first heating. We use semi-numerical hybrid methods to follow for the first time the joint evolution of the X-ray and Lyman-Werner radiative backgrounds, including the effect of the supersonic streaming velocity on the cosmic distribution of stars. We incorporate self-consistently the negative feedback on star formation induced by the Lyman-Werner radiation, which dissociates molecular hydrogen and thus suppresses gas cooling. We find that the feedback delays the X-ray heating transition by a Delta z ~ 2, but leaves a promisingly large fluctuation signal over a broad redshift range. The large-scale power spectrum is predicted to reach a maximal signal-to-noise ratio of S/N ~ 3-4 at z ~ 18 (for a projected first-generation instrument), with S/N > 1 out to z ~ 22-23. We hope to stimulate additional numerical simulations as well as observational efforts focused on the epoch prior to cosmic reionization.