The neutral hydrogen distribution in large-scale haloes from 21-cm intensity maps

We detect the neutral hydrogen (H I) radial brightness temperature profile in large-scale haloes by stacking 48 430 galaxies selected from the 2dFGRS catalogue on to a set of 21-cm intensity maps obtained with the Parkes radio telescope, spanning a total area of ∼1300 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 symmetrized version of the halo emission. We detect the H I 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 normalization c0,H I for the H I concentration parameter against the reconstructed profiles, using functional forms for the H I halo abundance proposed in the literature. We find log10 (Mv/M) = 16.1+−00.12, c0,H I = 3.5+−01.70 for the 10-mode and log10 (Mv/M) = 16.5+−00.12, c0,H I = 5.3+−11.17 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 subsamples of 13 979 central and 34 361 satellite 2dF galaxies separately, and obtain marginal differences suggesting satellite galaxies are H I-richer. This work shows for the first time the feasibility of testing theoretical models for the H I halo content directly on profiles extracted from 21-cm maps and opens future possibilities for exploiting upcoming H I intensity-mapping data.