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

Abstract

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 21cm21cm emission on 100deg2100deg2 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 ΩHIbHIrHI,optΩHIbHIrHI,opt at an effective scale keff, where ΩHIΩHI is the H I density fraction, bHIbHI is the H I bias, and rHI,optrHI,opt the galaxy–hydrogen correlation coefficient, which is dependent on the H I content of the optical galaxy sample. At keff=0.31hMpc−1keff=0.31hMpc−1 we find ΩHIbHIrHI,Wig=[0.58±0.09(stat)±0.05(sys)]×10−3ΩHIbHIrHI,Wig=[0.58±0.09(stat)±0.05(sys)]×10−3 for GBT-WiggleZ, ΩHIbHIrHI,ELG=[0.40±0.09(stat)±0.04(sys)]×10−3ΩHIbHIrHI,ELG=[0.40±0.09(stat)±0.04(sys)]×10−3 for GBT-ELG, and ΩHIbHIrHI,LRG=[0.35±0.08(stat)±0.03(sys)]×10−3ΩHIbHIrHI,LRG=[0.35±0.08(stat)±0.03(sys)]×10−3 for GBT-LRG, at z ≃ 0.8. We also report results at keff=0.24keff=0.24 and keff=0.48hMpc−1keff=0.48hMpc−1⁠. With little information on H I parameters beyond our local Universe, these are amongst the most precise constraints on neutral hydrogen density fluctuations in an underexplored redshift range