Reconstructing large scales at cosmic dawn

The cosmic microwave background (CMB) serves as a backlight to large-scale structure during the epoch of reionization, where Thomson scattering gives rise temperature anisotropies on small angular scales from kinetic Sunyaev Zel'dovich (kSZ) effect. In this paper, we demonstrate that technique kSZ tomography (velocity reconstruction), based cross correlations between CMB and 21cm surveys, can significantly improve constraints models inhomogeneous reionization provide information about modes are poorly characterized by measurements themselves due foreground contamination.