Probing large-scale filaments with H I and 3He II

Abstract

We explore the observability of the neutral hydrogen (H i) and the singly-ionized isotope helium-3 ( 3 He ii) in the intergalactic medium (IGM) from the Epoch of Reionization down to the local Universe. The hyperfine transition of 3 He ii, which is not as well known as the H i transition, has energy splitting corresponding to 8 cm. It also has a larger spontaneous decay rate than that of neutral hydrogen, whereas its primordial abundance is much smaller. Although both species are mostly ionized in the IGM, the balance between ionization and recombination in moderately high density regions renders them abundant enough to be observed. We estimate the emission signal of both hyperfine transitions from large scale filamentary structures and discuss the prospects for observing them with current and future radio telescopes. We conclude that H i in filaments is possibly observable even with current telescopes after 100 hours of observation. On the other hand, 3 He ii is only detectable with future telescopes, such as SKA, after the same amount of time.

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

“…There have been subsequent studies focused on the prediction of properties of the neutral baryonic component based on numerical simulations (Duffy et al 2012;Cunnama et al 2014), although most of them do not target specifically the study of HI in filaments. The detectability of filamentary neutral gas using 21-cm observations has been investigated by Takeuchi et al (2014). In that work the evolution of the abundance of different hydrogen ionisation states and the gas temperature in the IGM are at first computed analytically; the results enable the prediction of the typical HI brightness temperature and column density expected in filaments.…”

Filament hunting: integrated H i 21 cm emission from filaments inferred by galaxy surveys

“…To test the effect of the spin temperature correction term on the resulting signal of a filament, we assume a simple 0 1 2 3 4 5 z 10 0 10 1 10 2 10 3 10 4 constant density slab model. The signal from such a slab is calculated through a small adjustment of Equation 7, giving (Takeuchi et al 2014)…”

“…However, shielding from ionizing radiation due to recombinations in the denser pockets of gas still allows some of this gas to have a higher neutral fraction and emit potentially observable HI 21 cm radiation. Generally, the neutral fraction in these regions is well below a percent of the total gas content (Popping & Braun 2011;Takeuchi et al 2014). Nonetheless, its existence has been proved observationally through Lyman alpha forest absorption in the spectra of high redshift quasars (Gunn & Peterson 1965).…”

Probing primordial 3He from hyperfine line afterglows around supercritical black holes

“…Balser & Bania 2018;Bania et al 2010;Balser et al 2006). Takeuchi et al (2014) studied the possibility of detecting the hyperfine line in emission from the intergalactic low-overdensity gas exposed to the cumulative ionizing background at z < ∼ 10 (see also Bell 2000; Bagla & Loeb 2009). In this paper, we study the emission of this line from ionized regions surrounding growing black holes in the redshift range 12 < z < 25 and investigate its detectebility using the upcoming radio interferometer SKA1-MID.…”