H i constraints from the cross-correlation of eBOSS galaxies and Green Bank Telescope intensity maps

We present the joint analysis of Neutral Hydrogen (H i) Intensity Mapping observations with three galaxy samples: the Luminous Red Galaxy (LRG) and Emission Line Galaxy (ELG) samples from the eBOSS survey, and the WiggleZ Dark Energy Survey sample. The H i intensity maps are Green Bank Telescope observations of the redshifted 21 cm emission on 100, deg2 covering the redshift range 0.6 < z < 1.0. We process the data by separating and removing the foregrounds present in the radio frequencies with FastI ICA. We verify the quality of the foreground separation with mock realizations, and construct a transfer function to correct for the effects of foreground removal on the H i signal. We cross-correlate the cleaned H i data with the galaxy samples and study the overall amplitude as well as the scale dependence of the power spectrum. We also qualitatively compare our findings with the predictions by a semianalytical galaxy evolution simulation. The cross-correlations constrain the quantity Ω HI b HI r HI, opt at an effective scale keff, where Ω HI is the HI density fraction, bHI is the HI bias, and r HI, opt the galaxy-hydrogen correlation coefficient, whicHIs dependent on the HI content of the optical galaxy sample. At k eff=0.31 \, h, Mpc-1 we find Ω HI b HI r HI Wig = [0.58 ± 0.09 (stat) ± 0.05 (sys)] × 10-3 for GBT-WiggleZ, Ω HI b HI r HI, ELG = [0.40 ± 0.09 (stat) ± 0.04 (sys)] × 10-3 for GBT-ELG, and Ω HI b HI r HI,LRG = [0.35 ± 0.08 (stat) ± 0.03 (sys)] × 10-3 for GBT-LRG, at z 0.8. We also report results at k eff=0.24 and k eff=0.48 h Mpc-1. With little information on HI parameters beyond our local Universe, these are amongst the most precise constraints on neutral hydrogen density fluctuations in an underexplored redshift range.