Searching for HI imprints in cosmic web filaments with 21-cm intensity mapping

Abstract

We investigate the possible presence of neutral hydrogen (HI) in intergalactic filaments at very low redshift ($z\sim 0.08$), by stacking a set of 274,712 2dFGRS galaxy pairs over 21-cm maps obtained with dedicated observations conducted with the Parkes radio telescope, over a total sky area of approximately 1,300 square degrees covering two patches in the northern and in the southern Galactic hemispheres. The stacking is performed by combining local maps in which each pair is brought to a common reference frame; the resulting signal from the edge galaxies is then removed to extract the filament residual emission. We repeat the analysis on maps cleaned removing either 10 or 20 foreground modes in a principal component analysis. Our study does not reveal any clear HI excess in the considered filaments in either case; we determine upper limits on the total filament HI brightness temperature at $T_{\mathrm{b}}\lesssim 10.3\mu \text{K}$ for the 10-mode and at $T_{\mathrm{b}}\lesssim 4.8\mu \text{K}$ for the 20-mode removed maps at the 95% confidence level. These estimates translate into upper limits for the local filament HI density parameter, ${\Omega }_{\mathrm{HI}}^{(\mathrm{f})}\lesssim 7.0\times 10^{-5}$ and ${\Omega }_{\mathrm{HI}}^{(\mathrm{f})}\lesssim 3.2\times 10^{-5}$ respectively, and for the HI column density, $N_{\mathrm{HI}}\lesssim 4.6\times 10^{15}{\text{cm}}^{-2}$ and $N_{\mathrm{HI}}\lesssim 2.1\times 10^{15}{\text{cm}}^{-2}$ respectively. These column density constraints are consistent with previous detections of HI in the warm-hot intergalactic medium obtained observing broad Ly $\alpha$ absorption systems. The present work shows for the first time how such constraints can be achieved using the stacking of galaxy pairs on 21-cm maps.

Accepted for publication by MNRAS. 18 pages, 11 figures

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• Probing Diffuse Gas with Fast Radio Bursts
• The neutral hydrogen distribution in large-scale haloes from 21-cm intensity maps
• Probing the Diffuse Lyman-alpha Emission on Cosmological Scales: Lyα Emission Intensity Mapping Using the Complete SDSS-IV eBOSS Survey
• The Population of Galaxies that Contribute to The HI Mass Function
• Emission-line Stacking of 21cm Intensity Maps with MeerKLASS: Inference Pipeline and Application to the L-band Deep-field Data
• Expanded Generalized Needlet Internal Linear Combination (eGNILC) Framework for the 21-cm Foreground Removal
• FAST drift scan survey for HI intensity mapping: simulation on hunting HI filament with pairwise stacking
• A 15 Mpc rotating galaxy filament at redshift z = 0.032
• Detection of HI filament: Pair Stacking vs. Filament Stacking
• Squared-field cross-correlation between kinetic Sunyaev-Zel'dovich effect and 21-cm intensity mapping