Probing the high-z IGM with the hyperfine transition of 3He+

Abstract

<jats:title>Abstract</jats:title> <jats:p>The hyperfine transition of 3He+ at 3.5 cm has been thought as a probe of the high-z IGM since it offers a unique insight into the evolution of the helium component of the gas, as well as potentially give an independent constraint on the 21 cm signal from neutral hydrogen. In this paper, we use radiative transfer simulations of reionization driven by sources such as stars, X-ray binaries, accreting black holes and shock heated interstellar medium, and simulations of a high-z quasar to characterize the signal and analyze its prospects of detection. We find that the peak of the signal lies in the range ∼1 − 50 μK for both environments, but while around the quasar it is always in emission, in the case of cosmic reionization a brief period of absorption is expected. As the evolution of HeII is determined by stars, we find that it is not possible to distinguish reionization histories driven by more energetic sources. On the other hand, while a bright QSO produces a signal in 21 cm that is very similar to the one from a large collection of galaxies, its signature in 3.5 cm is very peculiar and could be a powerful probe to identify the presence of the QSO. We analyze the prospects of the signal’s detectability using SKA1-mid as our reference telescope. We find that the noise power spectrum dominates over the power spectrum of the signal, although a modest S/N ratio can be obtained when the wavenumber bin width and the survey volume are sufficiently large.</jats:p>

Investigating X-ray sources during the epoch of reionization with the 21 cm signal

“…The simulations have been extensively discussed in Eide et al (2018) and Eide et al (2020b), hereafter E18 and E20 respectively, and have also been used to study e.g. the cross-correlation between the 21 cm signal and the Xray background (Ma et al 2018a), or the [OIII] emitters (Moriwaki et al 2019), as well as the modelling and observability of the 3 He + line from singly ionized helium (Khullar et al 2020). For more details about these simulations we refer the reader to Khandai et al (2015), E18 and E20, while here we just briefly summarize their main characteristics.…”

Nucleosynthetic signatures of primordial origin around supermassive black holes

“…In principle, the hyperfine transition of 3 He II at 8.66 GHz (3.5 cm) could be detected with future radio surveys and, in conjunction with HI 21 cm observations, could probe the primordial Helium abundance [17,18]. Although this signal is weak, future radio surveys with sufficient survey volume and wavenumber bandwidth could detect it during the epoch of reionization, when He II is abundant Ref.…”

“…Although this signal is weak, future radio surveys with sufficient survey volume and wavenumber bandwidth could detect it during the epoch of reionization, when He II is abundant Ref. [18]. In practice, in any surviving primordial gas near the quasar BH, Helium is likely to be doubly ionized (He III), unless it is shielded from the quasar's far-UV radiation, or the quasar is exceptionally young, making this detection unlikely.…”

Primordial helium-3 redux: The helium isotope ratio of the Orion nebula

“…Galactic H ii regions, it may be possible (but extremely challenging) to detect 3 He + emission around growing supermassive black holes at redshift z > 12 (Vasiliev et al 2019), provided that the quasar environment retains a primordial composition. Another possibility is to detect the 3 He + 8.7 GHz transition in absorption against the spectrum of a radio bright quasar during helium reionization (at redshift z ∼ 3; McQuinn & Switzer 2009;Takeuchi et al 2014;Khullar et al 2020). One advantage of this approach is that the gas in the intergalactic medium is largely unprocessed, and the 3 He/H value would therefore closely reflect the primordial value.…”