Cross correlation with Tianlai 21cm survey & DESI

The density fluctuations in the matter distribution are only visible through tracers (e.g. galaxies and photons) and precise measurements require large survey area and number density. Neutral hydrogen emits radio waves at 21cm and provides an economic way to trace 3D distribution of matter through a so-called “intensity mapping” method. However, the 21cm signal is strongly contaminated by foregrounds. Tianlai is an intensity mapping experiment of cylinders and dishes, covering the 700-800 MHz range and mapping HI density on the northern sky. We simulated cross-correlation of HI radio emission from Tianlai with optical galaxies from DESI, showing that detection is enhanced, and effect of foregrounds alleviated.