Abstract We report the detection of 21 cm emission at an average redshift z ¯ = 2.3 in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements ...of the Ly α forest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 < z < 2.5) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales with k ∥ ≲ 0.13 Mpc −1 at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Ly α forest flux transmission spectra to estimate the 21 cm–Ly α cross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9 σ detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼6–10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and they set the stage for future 21 cm intensity mapping analyses at z > 1.8.
We report the detection of 21 cm emission at an average redshift $\bar{z} =
2.3$ in the cross-correlation of data from the Canadian Hydrogen Intensity
Mapping Experiment (CHIME) with measurements of ...the Lyman-$\alpha$ forest from
eBOSS. Data collected by CHIME over 88 days in the $400-500$~MHz frequency band
($1.8 < z < 2.5$) are formed into maps of the sky and high-pass delay filtered
to suppress the foreground power, corresponding to removing cosmological scales
with $k_\parallel \lesssim 0.13\ \text{Mpc}^{-1}$ at the average redshift.
Line-of-sight spectra to the eBOSS background quasar locations are extracted
from the CHIME maps and combined with the Lyman-$\alpha$ forest flux
transmission spectra to estimate the 21 cm-Lyman-$\alpha$ cross-correlation
function. Fitting a simulation-derived template function to this measurement
results in a $9\sigma$ detection significance. The coherent accumulation of the
signal through cross-correlation is sufficient to enable a detection despite
excess variance from foreground residuals $\sim6-10$ times brighter than the
expected thermal noise level in the correlation function. These results are the
highest-redshift measurement of \tcm emission to date, and set the stage for
future 21 cm intensity mapping analyses at $z>1.8$.
We report the detection of 21 cm emission at an average redshift \(\bar{z} = 2.3\) in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements ...of the Lyman-\(\alpha\) forest from eBOSS. Data collected by CHIME over 88 days in the \(400-500\)~MHz frequency band (\(1.8 < z < 2.5\)) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales with \(k_\parallel \lesssim 0.13\ \text{Mpc}^{-1}\) at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyman-\(\alpha\) forest flux transmission spectra to estimate the 21 cm-Lyman-\(\alpha\) cross-correlation function. Fitting a simulation-derived template function to this measurement results in a \(9\sigma\) detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals \(\sim6-10\) times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of \tcm emission to date, and set the stage for future 21 cm intensity mapping analyses at \(z>1.8\).
