  In this paper we use radiative transfer + N-body simulations to explore the
feasibility of measurements of cross-correlations between the 21cm field
observed by the Square Kilometer Array (SKA) and high-z Lyman Alpha Emitters
(LAEs) detected in galaxy surveys with the Subaru Hyper Supreme Cam (HSC),
Subaru Prime Focus Spectrograph (PFS) and Wide Field Infrared Survey Telescope
(WFIRST). 21cm-LAE cross-correlations are in fact a powerful probe of the epoch
of reionization as they are expected to provide precious information on the
progress of reionization and the typical scale of ionized regions at different
redshifts. The next generation observations with SKA will have a noise level
much lower than those with its precursor radio facilities, introducing a
significant improvement in the measurement of the cross-correlations. We find
that an SKA-HSC/PFS observation will allow to investigate scales below ~10
Mpc/h and ~60 Mpc/h at z=7.3 and 6.6, respectively. WFIRST will allow to access
also higher redshifts, as it is expected to observe spectroscopically ~900 LAEs
per square degree and unit redshift in the range 7.5<z<8.5. Because of the
reduction of the shot noise compared to HSC and PFS, observations with WFIRST
will result in more precise cross-correlations and increased observable scales.
