Searching for H i 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 ∼ 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 b 10.3 µK for the 10-mode and at T b 4.8 µK for the 20-mode removed maps at the 95% confidence level. These estimates translate into upper limits for the local filament HI density parameter, Ω (f) HI 7.0 × 10 −5 and Ω (f) HI 3.2 × 10 −5 respectively, and for the HI column density, N HI 4.6 × 10 15 cm −2 and N HI 2.1 × 10 15 cm −2 respectively. These column density constraints are consistent with previous detections of HI in the warm-hot intergalactic medium obtained observing broad Ly α 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.

The population of galaxies that contribute to the H i mass function

“…Most of the HI observations using the stacking method were 1 http://cesam.lam.fr/zCosmos/ 2 https://cesam.lam.fr/vvds/ done with the Giant Metrewave Radio Telescope (GMRT). More recently stacking has been applied to estimate the HI content in filaments (Tramonte, et al 2019). However at higher redshifts (z ∼ 1.3) the stacking method did not result in a detection of star forming galaxies in the DEEP2 3 field (Kanekar, Sethi & Dwarakanath 2016) whereas positive detections have been reported by cross-correlating the HI Intensity map with an optical survey at z ∼ 0.8 (Chang, et al 2010;Masui, et al 2013).…”

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

“…Our choice reverted therefore to a set of 21-cm maps obtained with the Parkes telescope over the volume spanned by the 2dF galaxy catalogue, covering a large sky area of ∼ 1, 300 deg 2 over the redshift range 0.06 z 0.08. The same data set proved effective in Tramonte et al (2019) for a similar search of neutral gas in cosmic web filaments.…”

Detection of Cosmological 21 cm Emission with the Canadian Hydrogen Intensity Mapping Experiment

“…HI stacking analyses have previously been carried out on interferometric data from the Westerbork Synthesis Radio Telescope (Rhee et al 2013;Hu et al 2019Hu et al , 2020, the Giant Metrewave Radio Telescope (Lah et al 2007;Kanekar et al 2016;Rhee et al 2016Rhee et al , 2018Bera et al 2019;Chowdhury et al 2020) and the Very Large Array (Chen et al 2021a), as well as on single-antenna data from Parkes (Delhaize et al 2013;Tramonte et al 2019;Tramonte & Ma 2020) and the Arecibo Legacy Fast ALFA Survey (Guo et al 2020). The primary motivation of many of these studies was to improve our understanding of galaxy evolution by probing the reservoirs of HI that serve as fuel for star formation.…”