The global 21-centimeter background from high redshifts

By S. Furlanetto. 2006

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We consider the evolution of the sky-averaged 21-cm background during the early phases of structure formation. Using simple analytic models, we calculate the thermal and ionization histories, assuming that stellar photons dominate the radiation background. The resulting 21-cm spectra can constrain the properties of the first generations of stars and quasars. If Population II stars dominate, Lyα coupling renders the intergalactic medium (IGM) visible before it is heated by X-rays and long before reionization. Thus the 21-cm background has a strong absorption epoch followed by weaker emission that fades during reionization. The harder spectra of very massive Population III stars compress these transitions into a shorter time interval and decreases the signal amplitude. However, the reionization epoch will remain visible except in extreme cases. The global 21-cm signal will be challenging to observe because of astronomical foregrounds, but it offers an exciting opportunity to study the first sources of light. It also fixes the overall amplitude of the fluctuating background whose detection is a major goal of several next-generation low-frequency radio interferometers.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d008c10997c02ce43f03b9b9b18fb7e503397dd6

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Citations in the corpus

Hydrogen Epoch of Reionization Array (HERA) (2016, background): “The IGM is then expected to be heated by first generation X–ray binaries (Furlanetto 2006; Pritchard & Furlanetto 2007; Mesinger et al. 2013) or by the hot interstellar medium produced by the first supernovae (Pacucci et al. 2014), although the heating timing and magnitude is still very much…”
Efficient Simulations of Early Structure Formation and Reionization (2007, background): “The final approximation makes the standard assumption that TS ≫ Tγ for all redshifts of interest during reionization (e.g. Furlanetto 2006) and also that dvr/dr ≪ H .”
What does the first highly redshifted 21-cm detection tell us about early galaxies? (2018, methodology): “We employ a simple model for the global 21-cm signal in which the IGM is partitioned into two phases (e.g. Furlanetto 2006; Pritchard & Loeb 2010).”
Charting the parameter space of the global 21-cm signal (2016, methodology): “Its characteristic structure of peaks and troughs encodes information about global cosmic events (Furlanetto 2006).”
Comparison of reionization models: radiative transfer simulations and approximate, seminumeric models (2010, result): “We assume TS ≫ TCMB, which previous studies have concluded should be accurate throughout most of reionization (e.g., Furlanetto 2006; Pritchard & Furlanetto 2007).”
21cmfast: a fast, seminumerical simulation of the high‐redshift 21‐cm signal (2010, methodology): “For fiducial astrophysical models, this is likely a safe assumption during the bulk of reionization (Furlanetto 2006; Chen & Miralda-Escudé 2008; Santos et al. 2008; Baek et al. 2009).”
21-cm fluctuations from inhomogeneous X-ray heating before reionization (2006, methodology): “III (f esc = 0.1, f = 0.01, N ion = 30 000) stars (Furlanetto 2006), although we note that these values are highly uncertain.”
The Evolution of the Intergalactic Medium (2015, background): “…a relatively uniform ionization floor before ultraviolet photons finished the job, with empirically motivated models predicting a floor of 0.1−1% (Furlanetto 2006; Pober et al. 2015), although the modeling uncertainties are immense. over d3x dΩ dν ν2 yields ̄γ = Γn̄HI︷︸︸︷( ˙̄nHI + CαB,4…”
Inside-out or outside-in: the topology of reionization in the photon-starved regime suggested by Lyα forest data (2008, background): “…(a few percent) of the volume/mass has been ionized (Scott & Rees 1990; Tozzi et al. 2000; Ciardi & Madau 2003; Barkana & Loeb 2005; Sethi 2005; Furlanetto 2006; Furlanetto, Oh, & Briggs 2006; see Pritchard & Loeb 2008 for an extensive recent discussion of the expectedevolution of the spin…”
Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, unknown): “…expressed as the offset of the 21-cm brightness temperature, δTb(ν), relative to the temperature of the cosmic microwave background (CMB), TCMB (e.g. Furlanetto 2006): δTb ≈ 27xH i(1 + δnl) ( H dvr/dr + H ) ( 1 − TCMB TS ) × ( 1 + z 10 0.15 Ωmh2 )1/2 ( Ωbh2 0.023 ) , (14) where xH i is the…”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, background): “The positions of the various turning points would pin down the redshifts when the first galaxies and X-ray sources form and when reionization began and ended (Furlanetto 2006b; Pritchard & Loeb 2010).”
Signatures of X-rays in the early Universe (2012, methodology): “This run differs from the fiducial only in having an X-ray efficiency which is a factor of ≈5 higher, making it more in line with several previous works (e.g. Furlanetto 2006; Pritchard & Furlanetto 2007; Santos et al. 2008; Warszawski et al. 2009; Mack & Wyithe 2011; Valdés et al. 2012).”
Simulations and Analytic Calculations of Bubble Growth during Hydrogen Reionization (2006, background): “At the redshifts we consider presently, the 21 cm excitation temperature is likely coupled to the gas temperature, and much larger than the temperature of the CMB (e.g. Furlanetto 2006; Chen & Miralda-Escude 2004; Ciardi & Madau 2003), TS >> TCMB, implying δT ∝ (1 + δs)xH .”
The morphology of H ii regions during reionization (2006, background): “We also assume Ts TCMB in this section, likely a good approximation during the bulk of the reionization epoch (Ciardi & Madau 2003; Furlanetto 2006).”
Stellar black holes at the dawn of the universe (2011, methodology): “When modeling the impact of X-ray emission from galaxies at very high redshift, the following more general correlation is used (Furlanetto 2006): L2−10 = fX × 3.5 × 1040 × SFR erg s−1.”
Fundamental physics with the Square Kilometre Array (2018, background): “After thermal decoupling at z ∼ 150, the gas temperature is expected to cool adiabatically, with a phase of X-ray heating from galaxies warming the gas, before the photoionisation heating during reionisation raises the temperature to ∼ 104 K (e.g. Furlanetto, 2006; McQuinn & O’Leary, 2012).”