Forecasting the cross-correlation of the CSST galaxy survey with the FAST H i Intensity Map

Abstract

ABSTRACT The cross-correlation of optical galaxies with the neutral hydrogen (H i) radiation intensity can enhance the signal-to-noise ratio (SNR) of the H i intensity measurement. In this paper, we investigate the cross-correlation of the galaxy samples obtained by the spectroscopic survey of the China Space Station Telescope (CSST) with the H i Intensity mapping (IM) survey of the Five-hundred-meter Aperture Spherical Telescope (FAST). Using the IllusitrisTNG simulation result at redshift 0.2 ∼ 0.3, we generate mock data of the CSST survey and a FAST L-band drift scan survey. The CSST spectroscopic survey can yield a sample of galaxies with a high comoving number density of $10^{-2}\, ({\ \rm Mpc}\,h^{ -1})^{-3}$ at z ∼ 0.3. We cross-correlate the foreground-removed radio intensity with the CSST galaxies, including both the whole sample, and red and blue galaxy subsamples separately. We find that in all cases the H i and optical galaxies are well correlated. The total H i abundance can be measured with a high precision from this correlation. A relative error of $\sim 0.6{{\ \rm per\ cent}}$ for $\Omega _{\rm H\, \small {I}}$ could be achieved at z ∼ 0.3 for an overlapping survey area of $10\,000\, {\ \rm deg}^2$.