Cross-correlation of the cosmic 21-cm signal and Lyman Alpha Emitters during reionization

TL;DR

This paper investigates the cross-correlation between Lyman Alpha Emitters and the 21-cm signal during reionization, demonstrating its robustness and potential to distinguish different ionization states with current and future radio telescopes.

Contribution

It provides a systematic analysis of LAE-21cm cross-correlation as a robust probe of reionization, assessing detectability with LOFAR and SKA1 under various assumptions.

Findings

LOFAR can distinguish fully ionized from partially neutral universe with 1000h observation.

SKA1 can differentiate between ionization states with 100h survey despite uncertainties.

LAE-21cm cross-correlation is insensitive to LAE host assignment prescriptions.

Abstract

Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal-to-noise, limited by systematics. To confirm a putative 21-cm detection, and check the accuracy of 21-cm data analysis pipelines, it would be very useful to cross-correlate against a genuine cosmological signal. The most promising cosmological signals are wide-field maps of Lyman alpha emitting galaxies (LAEs), expected from the Subaru Hyper-Suprime Cam (HSC) Ultra-Deep field. Here we present estimates of the correlation between LAE maps at z~7 and the 21-cm signal observed by both the Low Frequency Array (LOFAR) and the planned Square Kilometer Array Phase 1 (SKA1). We adopt a systematic approach, varying both: (i) the prescription of assigning LAEs to host halos; and (ii) the large-scale structure of neutral and ionized regions (i.e. EoR morphology). We find that the LAE-21cm cross-correlation is insensitive to (i), thus making it a robust probe of the EoR. A 1000h observation with LOFAR would be sufficient to discriminate at >1 standard deviation a fully ionized Universe from one with a mean neutral fraction of xHI~0.50, using the LAE-21cm cross-correlation function on scales of R~3-10 Mpc. Unlike LOFAR, whose detection of the LAE-21cm cross-correlation is limited by noise, SKA1 is mostly limited by ignorance of the EoR morphology. However, the planned 100h wide-field SKA1-Low survey will be sufficient to discriminate an ionized Universe from one with xHI~0.25, even with maximally pessimistic assumptions.