Cross-correlating 21cm intensity maps with Lyman Break Galaxies in the post-reionization era

TL;DR

This study forecasts the detectability of the cross-correlation between Lyman Break Galaxies and 21cm intensity maps at redshifts 3-5, demonstrating a significantly higher signal-to-noise ratio compared to the 21cm auto-spectrum, with robustness against foreground contamination.

Contribution

It presents the first detailed forecast of LBG-21cm cross-spectrum detection at high redshifts using simulations, highlighting its advantages over auto-spectrum measurements and foreground robustness.

Findings

Cross-correlation can be detected with high SNR (~10)

Cross-spectrum is more robust to foreground contamination

Detection is feasible across a range of redshifts and galaxy populations

Abstract

We investigate the cross-correlation between the spatial distribution of Lyman Break Galaxies (LBGs) and the 21cm intensity mapping signal at $z\sim[3-5]$. At these redshifts, galactic feedback is supposed to only marginally affect the matter power spectrum, and the neutral hydrogen distribution is independently constrained by quasar spectra. Using a high resolution N-body simulation, populated with neutral hydrogen a posteriori, we forecast for the expected LBG-21cm cross-spectrum and its error for a 21cm field observed by the Square Kilometre Array (SKA1-LOW and SKA1-MID), combined with a spectroscopic LBG survey with the same volume. The cross power can be detected with a signal-to-noise ratio (SNR) up to ~10 times higher (and down to ~4 times smaller scales) than the 21cm auto-spectrum for this set-up, with the SNR depending only very weakly on redshift and the LBG population. We also show that while both the 21cm auto- and LBG-21cm cross-spectra can be reliably recovered after the cleaning of smooth-spectrum foreground contamination, only the cross-power is robust to problematic non-smooth foregrounds like polarized synchrotron emission.