The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared ( NIR ) background light from the high-redshift galaxies promises to be a powerful probe of cosmic reionization .
In this paper , we investigate the cross power spectrum during the epoch of reionization .
We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model : metal-free stars and metal-poor stars .
The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements .
Then the intensity of NIR background is estimated by collecting emission from stars in the first-light galaxies .
On large scales , we find the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization .
However , these two radiation backgrounds quickly become anti-correlated as reionization proceeds .
The maximum absolute value of the cross power spectrum is | \Delta ^ { 2 } _ { 21 ,NIR } | \sim 10 ^ { -4 } mK nW m ^ { -2 } sr ^ { -1 } reached at \ell \sim 1000 , when the mean fraction of ionized hydrogen is \bar { x } _ { i } \sim 0.9 .
We find that SKA can measure the 21 cm-NIR cross power spectrum in conjunction with mild extensions to the existing CIBER survey , provided that the integration time independently adds up to 1000 and 1 hours for 21 cm and NIR observations , and that the sky coverage fraction of CIBER survey is extended from 4 \times 10 ^ { -4 } to 0.1 .
Measuring the cross-correlation signal as a function of redshift provides valuable information on reionization and helps confirm the origin of the “ missing ” NIR background .