Hydrogen 2<i>p</i>–2<i>s</i>Transition: Signals from the Epochs of Recombination and Reionization

Sethi, Shiv K.; Subrahmanyan, R.; Roshi, D. Anish

doi:10.1086/518650

Cited by 6 publications

(9 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In particular, bright quasars that are luminous in the restframe soft-UV (10.2 eV < Eγ < 13.6 eV) may indirectly photoexcite the 2s state of neutral hydrogen gas in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) to levels such that τF S ∼ 10 −5 for CMB photons passing through these regions (Sethi et al 2007). The resulting brightness temperature of ∆T b ∼ tens of µK could be detected with existing radio telescopes (e.g.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

Dijkstra

Lidz

Pritchard

et al. 2008

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

A soft ultraviolet radiation field, 10.2 < hν < 13.6 eV, that permeates neutral intergalactic gas during the epoch of reionization (EoR) excites the 2p (directly) and 2s (indirectly) states of atomic hydrogen. Because the 2s state is metastable, the lifetime of atoms in this level is relatively long, which may cause the 2s state to be overpopulated relative to the 2p state. It has recently been proposed that for this reason, neutral intergalactic atomic hydrogen gas may be detected in absorption in its 3‐cm fine‐structure line (2s1/2→ 2p3/2) against the cosmic microwave background out to very high redshifts. In particular, the optical depth in the fine‐structure line through neutral intergalactic gas surrounding bright quasars during the EoR may reach τFS∼ 10−5. The resulting surface brightness temperature of tens of μK (in absorption) may be detectable with existing radio telescopes. Motivated by this exciting proposal, we perform a detailed analysis of the transfer of Lyβ, γ, δ, … radiation, and reanalyse the detectability of the fine‐structure line in neutral intergalactic gas surrounding high‐redshift quasars. We find that proper radiative transfer modelling causes the fine‐structure absorption signature to be reduced tremendously to τFS≲ 10−10. We therefore conclude that neutral intergalactic gas during the EoR cannot reveal its presence in the 3‐cm fine‐structure line to existing radio telescopes.

show abstract

Section: Discussionmentioning

confidence: 99%

“…It has recently been proposed that it may be possible to observe neutral atomic hydrogen gas during the epoch of reionization (EoR), in absorption against the cosmic microwave background (CMB) in its 3‐cm fine‐structure line (2s 1/2 → 2p 3/2 , Sethi, Subrahmanyan & Roshi 2007, hereafter S07).…”

Section: Introductionmentioning

confidence: 99%

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

Dijkstra

Lidz

Pritchard

et al. 2008

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…We search for any atom or molecule that may be present in the high redshift Universe. This includes molecules that form from the primordial elements H, D, He and Li (Steigman 2007) Sethi et al 2007;Chluba et al 2007;Rubiño-Martín et al 2008). Prior to the reionisation at z > ∼ 6 the universe was, however, opaque to for instance Lyα radiation (Becker et al 2001).…”

Section: Interesting Speciesmentioning

confidence: 99%

“…This includes molecules that form from the primordial elements H, D, He and Li (Steigman, 2007) such as: H 2 , H + 2 , H 2 D + , HD, HD + , HeH + , LiH and LiH + . There are also suggestions that lines from neutral hydrogen H and helium He could be seen during the time of respective recombination and at later times (Rubiño-Martín et al, 2006;Sethi et al, 2007;Chluba et al, 2007;Rubiño-Martín et al, 2008). Prior to the reionisation at z 6 the universe was, however, opaque to for instance Lyα radiation (Becker et al, 2001).…”

Section: Interesting Speciesmentioning

confidence: 99%

The first spectral line surveys searching for signals from the dark ages

Persson¹,

Maoli

Encrenaz

et al. 2010

A&A

View full text Add to dashboard Cite

Aims. Our aim is to observationally investigate the cosmic Dark Ages in order to constrain star and structure formation models, as well as the chemical evolution in the early Universe. Methods. Spectral lines from atoms and molecules in primordial perturbations at high redshifts can give information about the conditions in the early universe before and during the formation of the first stars in addition to the epoch of reionisation. The lines may arise from moving primordial perturbations before the formation of the first stars (resonant scattering lines), or could be thermal absorption or emission lines at lower redshifts. The difficulties in these searches are that the source redshift and evolutionary state, as well as molecular species and transition are unknown, which implies that an observed line can fall within a wide range of frequencies. The lines are also expected to be very weak. Observations from space have the advantages of stability and the lack of atmospheric features which is important in such observations. We have therefore, as a first step in our searches, used the Odin satellite to perform two sets of spectral line surveys towards several positions. The first survey covered the band 547−578 GHz towards two positions, and the second one covered the bands 542.0−547.5 GHz and 486.5−492.0 GHz towards six positions selected to test different sizes of the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz with 1 GHz bandwidth were also performed towards one position. The two lowest rotational transitions of H 2 will be redshifted to these frequencies from z ∼ 20−30, which is the predicted epoch of the first star formation. Results. No lines are detected at an rms level of 14−90 and 5−35 mK for the two surveys, respectively, and 2−7 mK in the deep searches with a channel spacing of 1−16 MHz. The broad bandwidth covered allows a wide range of redshifts to be explored for a number of atomic and molecular species and transitions. From the theoretical side, our sensitivity analysis show that the largest possible amplitudes of the resonant lines are about 1 mK at frequencies < ∼ 200 GHz, and a few μK around 500−600 GHz, assuming optically thick lines and no beam-dilution. However, if existing, thermal absorption lines have the potential to be orders of magnitude stronger than the resonant lines. We make a simple estimation of the sizes and masses of the primordial perturbations at their turnaround epochs, which previously has been identified as the most favourable epoch for a detection. This work may be considered as an important pilot study for our forthcoming observations with the Herschel Space Observatory.

show abstract

“…We therefore conclude that the use of the radiometer equation for gauging the detectability of the 21cm signal is justified by the flood of noise photons from the sky that accompanies the seeked-after signal. It is important to keep this point in mind when considering the detectability of other spectral lines [22,23,24,25] or continuum emission [26,27] from the diffuse cosmic gas, especially at wavelengths shorter than a millimeter -where the Wien tail of the CMB or other foregrounds are not as bright.…”

mentioning

confidence: 99%

Is a classical language adequate in assessing the detectability of the redshifted 21 cm signal from the early Universe?

Loeb

2008

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

The classical radiometer equation is commonly used to calculate the detectability of the 21cm emission by diffuse cosmic hydrogen at high redshifts. However, the classical description is only valid in the regime where the occupation number of the photons in phase space is much larger than unity and they collectively behave as a classical electromagnetic field. At redshifts z 20, the spin temperature of the intergalactic gas is dictated by the radiation from galaxies and the brightness temperature of the emitting gas is in the range of mK, independently from the existence of the cosmic microwave background. In regions where the observed brightness temperature of the 21cm signal is smaller than the observed photon energy, hν = 68(1 + z) −1 mK, the occupation number of the signal photons is smaller than unity. Nevertheless, the radiometer equation can still be used in this regime because the weak signal is accompanied by a flood of foreground photons with a high occupation number (involving the synchrotron Galactic emission and the cosmic microwave background). As the signal photons are not individually distinguishable, the combined signal+foreground population of photons has a high occupation number, thus justifying the use of the radiometer equation. PACS numbers: 95.30Dr, 95.55Jz, A black-body radiation field of temperature T and a photon occupation number n = (exp{hν/kT } − 1) −1 , is characterized by fluctuations in the number of photons per quantum state with a root-mean-square amplitude of [1], ∆n rms = n(n + 1) = n 2 + n.(1)

show abstract

Hydrogen 2p–2sTransition: Signals from the Epochs of Recombination and Reionization

Cited by 6 publications

References 27 publications

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

The first spectral line surveys searching for signals from the dark ages

Is a classical language adequate in assessing the detectability of the redshifted 21 cm signal from the early Universe?

Contact Info

Product

Resources

About