Robust Intensity Mapping Analysis against Foregrounds for the Epoch of
  Reionization
  Intensity mapping of the HI 21 cm line and the CO 2.61 mm line from the epoch
of reionization has emerged as powerful, complementary, probes of the
high-redshift Universe. However, both maps and their cross-correlation are
dominated by foregrounds. We propose a new analysis by which the signal is
unbiased by foregrounds, i.e. it can be measured without foreground mitigation.
We construct the antisymmetric part of the HI-CO cross-correlation, arising
because the statistical fluctuations of two fields have different evolution in
time. We show that the sign of this new signal can distinguish
model-independently whether inside-out reionization happens during some
interval of time.
