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The cross-correlation between the 21 cm emission from the high-redshiftintergalactic medium and the near-infrared (NIR) background light from thehigh-redshift galaxies promises to be a powerful probe of cosmic reionization.In this paper, we investigate the cross power spectrum during the epoch ofreionization. We employ an improved halo approach to derive the distribution ofthe density field and consider two stellar populations in the star formationmodel: metal-free stars and metal-poor stars. The reionization history isfurther generated to be consistent with the electron-scattering optical depthfrom cosmic microwave background measurements. Then the intensity of NIRbackground is estimated by collecting emission from stars in the first-lightgalaxies. On large scales, we find the 21 cm and NIR radiation backgrounds arepositively correlated during the very early stages of reionization. However,these two radiation backgrounds quickly become anti-correlated as reionizationproceeds. The maximum absolute value of the cross power spectrum is$|\Delta^2_{\rm{21,NIR}}|\sim10^{-4}$ mK nW $\rm{m}^{-2}$ $\rm{sr}^{-1}$reached at $\ell\sim1000$, when the mean fraction of ionized hydrogen is$\bar{x}_{i}\sim0.9$. We find that SKA can measure the 21 cm-NIR cross powerspectrum in conjunction with mild extensions to the existing CIBER survey,provided that the integration time independently adds up to 1000 and 1 hoursfor 21 cm and NIR observations, and that the sky coverage fraction of CIBERsurvey is extended from $4\times10^{-4}$ to 0.1. Measuring thecross-correlation signal as a function of redshift provides valuableinformation on reionization and helps confirm the origin of the "missing" NIRbackground.

Probing reionization with the cross power spectrum of 21 cm and near-infrared radiation backgrounds