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 |$21\rm cm$| emission on |$100 \, {\rm deg}^2$| 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 |$\Omega _{\rm {H\,\small {I}}} b_{\rm {H\,\small {I}}} r_{\rm {H\,\small {I}},{\rm opt}}$| at an effective scale k _eff, where |$\Omega _\rm {H\,\small {I}}$| is the H   i density fraction, |$b_\rm {H\,\small {I}}$| is the H  i bias, and |$r_{\rm {H\,\small {I}},{\rm opt}}$| the galaxy–hydrogen correlation coefficient, which is dependent on the H   i content of the optical galaxy sample. At |$k_{\rm eff}=0.31 \, h\,{\rm Mpc^{-1}}$| we find |$\Omega _{\rm {H\,\small {I}}} b_{\rm {H\,\small {I}}} r_{\rm {H\,\small {I}},{\rm Wig}} = [0.58 \pm 0.09 \, {\rm (stat) \pm 0.05 \, {\rm (sys)}}] \times 10^{-3}$| for GBT-WiggleZ, |$\Omega _{\rm {H\,\small {I}}} b_{\rm {H\,\small {I}}} r_{\rm {H\,\small {I}},{\rm ELG}} = [0.40 \pm 0.09 \, {\rm (stat) \pm 0.04 \, {\rm (sys)}}] \times 10^{-3}$| for GBT-ELG, and |$\Omega _{\rm {H\,\small {I}}} b_{\rm {H\,\small {I}}} r_{\rm {H\,\small {I}},{\rm LRG}} = [0.35 \pm 0.08 \, {\rm (stat) \pm 0.03 \, {\rm (sys)}}] \times 10^{-3}$| for GBT-LRG, at z ≃ 0.8. We also report results at |$k_{\rm eff}=0.24$| and |$k_{\rm eff}=0.48 \, h\,{\rm Mpc^{-1}}$|⁠. 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. [ABSTRACT FROM AUTHOR]