Cosmology at low frequencies: The 21 cm transition and the high-redshift Universe

By S. Furlanetto, S. Oh, Frank H. Briggs. 2006

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Abstract Observations of the high-redshift Universe with the 21 cm hyperfine line of neutral hydrogen promise to open an entirely new window onto the early phases of cosmic structure formation. Here we review the physics of the 21 cm transition, focusing on processes relevant at high redshifts, and describe the insights to be gained from such observations. These include measuring the matter power spectrum at z ∼ 50 , observing the formation of the cosmic web and the first luminous sources, and mapping the reionization of the intergalactic medium. The epoch of reionization is of particular interest, because large HII regions will seed substantial fluctuations in the 21 cm background. We also discuss the experimental challenges involved in detecting this signal, with an emphasis on the Galactic and extragalactic foregrounds. These increase rapidly toward low frequencies and are especially severe for the highest redshift applications. Assuming that these difficulties can be overcome, the redshifted 21 cm line will offer unique insight into the high-redshift Universe, complementing other probes but providing the only direct, three-dimensional view of structure formation from z ∼ 200 to 6.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d83ac169f2b593cdf519ed3a598886d630c9544b

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Citations in the corpus

Studying reionization with Lyα emitters (2007, background): “However, 21cm observations must first overcome terrestrial radio broadcasts as well as galactic foregrounds that are four orders of magnitude larger than the signal (e.g., Zaldarriaga et al. 2004; McQuinn et al. 2006; Furlanetto et al. 2006).”
Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE) (2008, background): “This transition originates from magnetic moments or spins of the proton and electron – if the angular momenta are aligned, the atom lies at a slightly higher energy than if they are antialigned (Furlanetto et al., 2006).”
Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7 (2018, methodology): “We initialize the IGM temperature in ionized regions to the values from the hydrodynamical simulation skewer, and assume that the IGM is initially cold (2000 K) inside of neutral regions (e.g. Furlanetto et al. 2006).”
Upper Limits on the 21 cm Epoch of Reionization Power Spectrum from One Night with LOFAR (2017, background): “C It has been long recognized that the redshifted 21-cm emission line provides a very promising probe to observe neutral hydrogen during the EoR (see e.g. Madau et al. 1997; Shaver et al. 1999; Furlanetto et al. 2006; Pritchard & Loeb 2012; Zaroubi 2013).”
The physics of the intergalactic medium (2007, methodology): “Since then, there have been numerous estimates of their contribution to the UV metagalactic background (Bechtold et al., 1987; Fardal et al., 1998; Giroux and Shapiro, 1996; Haardt and Madau, 1996, 2001; Madau, 1992; Meiksin and Madau, 1993; Miralda-Escudé and Ostriker, 1990, 1992; Sargent et al., ”
Signatures of X-rays in the early Universe (2012, neutral): “…in terms of the offset of the 21cm brightness temperature from the CMB temperature, Tγ , along a line of sight (LOS) at observed frequency ν (c.f. Furlanetto et al. 2006): δTb(ν) = TS − Tγ 1 + z (1− e−τν0 ) ≈ 27xHI(1 + δnl) ( H dvr/dr +H )( 1− Tγ TS ) × ( 1 + z 10 0.15 ΩMh2 )1/2( Ωbh…”
21-cm fluctuations from inhomogeneous X-ray heating before reionization (2006, methodology): “Fluctuations in the 21-cm signal may be expanded as (Furlanetto et al. 2006) δTb = βδ + βxδx + βαδα + βTδT − δ∂v, (5) where each δi describes the fractional variation in the quantity i: δα for fluctuations in the Lyα coupling coefficient, δx for the neutral fraction, δT for TK and δ∂v for the…”
Fast large volume simulations of the 21-cm signal from the reionization and pre-reionization epochs (2009, background): “The radiative coupling is given by xα = SαJα Jc , (9) with Jc ≈ 5.552 × 10−8(1 + z) m−2s−1Hz−1sr−1 and Sα is a correction factor of order unity (Chen & Miralda-Escudé 2004; Hirata 2006; Chuzhoy & Shapiro 2007; Furlanetto & Pritchard 2006; Furlanetto et al. 2006).”
Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries (2016, background): “Because of inhomogeneities in the gas density field, hydrogen ionized fraction, and spin temperature, and of velocity gradients along the line of sight, the 21-cm signal will display angular structure, as well as structure in redshift space (see Furlanetto et al. 2006, for a review).”
Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude (2018, background): “The redshifted 21 cm line of neutral hydrogen (H I) offers a promising tool for mapping our universe’s “cosmic dawn,” when the first luminous sources formed (see Barkana & Loeb 2001; Furlanetto et al. 2006; Morales & Wyithe 2010; Pritchard & Loeb 2012; McQuinn 2016 for reviews).”
Science with a lunar low-frequency array: From the dark ages of the Universe to nearby exoplanets (2009, background): “The exploitation of cosmological 21-cm emission is subject of a rapidly developing literature, which is reviewed by Furlanetto et al. (2006).”
THE PRECISION ARRAY FOR PROBING THE EPOCH OF RE-IONIZATION: EIGHT STATION RESULTS (2009, methodology): “The most incisive probe of EoR is direct observation of the neutral IGM using the hydrogen 21cm line (Furlanetto et al. 2006; Barkana & Loeb 2005a).”
FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7 (2016, methodology): “(For reviews, see Furlanetto et al. 2006, Morales & Wyithe 2010, Zaroubi 2013, Loeb & Furlanetto 2013, and Pritchard & Loeb 2012) The first generation of instruments with primary science goals to detect the highly redshift 21cm signal have been built, including the GMRT (Giant Metrewave Radio…”
The morphology of H ii regions during reionization (2006, background): “This small difference is partly because Furlanetto et al. (2006a) underestimate the free path a photon will take inside a bubble.”
Early Cosmological H II/He III Regions and Their Impact on Second-Generation Star Formation (2006, background): “Finally, it has been long known that neutral hydrogen at high redshift may be directly detectable through the redshifted 21 cm line (see Furlanetto et al. 2006b for a recent review).”