neutral hydrogen distribution in large-scale haloes from 21-cm intensity maps | Monthly Notices of …


We detect the neutral hydrogen (HI) radial brightness temperature profile in large-scale haloes by stacking 48,430 galaxies selected from the 2dFGRS catalogue onto a set of 21-cm intensity maps obtained with the Parkes radio telescope, spanning a total area of ∼1,300 deg2 on the sky and covering the redshift range 0.06 ≲ z ≲ 0.10. Maps are obtained by removing both 10 and 20 foreground modes in the principal component analysis. We perform the stack at the map level and extract the profile from a circularly symmetrised version of the halo emission. We detect the HI halo emission with the significance 12.5σ for the 10-mode and 13.5σ for the 20-mode removed maps at the profile peak. We jointly fit for the observed halo mass Mv and the normalisation |$c_{0,rm HI}$| for the HI concentration parameter against the reconstructed profiles, using functional forms for the HI halo abundance proposed in the literature. We find |$log _{10}{(M_{rm v}/text{M}_{odot })}= 16.1^{+0.1}_{-0.2}$|⁠, |$c_{0,rm HI}=3.5^{+0.7}_{-1.0}$| for the 10-mode and |$log _{10}{(M_{rm v}/text{M}_{odot })}= 16.5^{+0.1}_{-0.2}$|⁠, |$c_{0,rm HI}=5.3^{+1.1}_{-1.7}$| for the 20-mode removed maps. These estimates show the detection of the integrated contribution from multiple galaxies located inside very massive haloes. We also consider sub-samples of 13,979 central and 34,361 satellite 2dF galaxies separately, and obtain marginal differences suggesting satellite galaxies are HI-richer. This work shows for the first time the feasibility of testing theoretical models for the HI halo content directly on profiles extracted from 21-cm maps and opens future possibilities for exploiting upcoming HI intensity-mapping data.

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© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

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