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

Abstract

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 $\sim$1,300 ${\text{deg}}^2$ on the sky and covering the redshift range $0.06\lesssim z\lesssim 0.10$. 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 $12.5\sigma$ for the 10-mode and $13.5\sigma$ for the 20-mode removed maps at the profile peak. We jointly fit for the observed halo mass $M_{\mathrm{v}}$ and the normalisation $c_{0,\mathrm{HI}}$ for the HI concentration parameter against the reconstructed profiles, using functional forms for the HI halo abundance proposed in the literature. We find ${\log }_{10}(M_{\mathrm{v}}/{\text{M}}_{\odot })=16.1_{-0.2}^{+0.1}$, $c_{0,\mathrm{HI}}=3.5_{-1.0}^{+0.7}$ for the 10-mode and ${\log }_{10}(M_{\mathrm{v}}/{\text{M}}_{\odot })=16.5_{-0.2}^{+0.1}$, $c_{0,\mathrm{HI}}=5.3_{-1.7}^{+1.1}$ 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.

20 pages, 13 figures. Accepted for publication in MNRAS

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• Probing the Diffuse Lyman-alpha Emission on Cosmological Scales: Lyα Emission Intensity Mapping Using the Complete SDSS-IV eBOSS Survey
• Emission-line Stacking of 21cm Intensity Maps with MeerKLASS: Inference Pipeline and Application to the L-band Deep-field Data
• Prospects for cosmological research with the FAST array: 21-cm intensity mapping survey observation strategies
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