Cosmic recombination history in light of EDGES measurements of the cosmic dawn 21-cm signal

Abstract

The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest that the kinetic temperature of the inter-galactic medium (IGM) might be significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of DM-baryonic interaction model which is widely used to explain the depth of the EDGES 21-cm signal. We find that, in general, the hydrogen ionisation fraction gets suppressed during the dark ages and cosmic dawn and the suppression gradually increases at lower redshifts until X-ray heating turns on. However, accurate estimation of the ionisation fraction requires knowledge of the entire thermal history of the IGM, from the epoch of thermal decoupling of hydrogen gas and the CMBR to the cosmic dawn. It is possible that two separate scenarios which predict very similar HI differential temperature during the cosmic dawn and are consistent with the EDGES 21-cm signal might have very different IGM temperature during the dark ages. The evolutions of the ionisation fraction in these two scenarios are quite different. This prohibits us to accurately calculate the ionisation fraction during the cosmic dawn using the EDGES 21-cm signal alone. We find that the changes in the ionisation fraction w.r.t the standard scenario at redshift $z\sim 17$ could be anything between $\sim 0\%$ to $\sim 36\%$. This uncertainty may be reduced if measurements of HI 21-cm differential temperature at multiple redshifts are simultaneously used.

arXiv comment10 pages, 8 figures. The revised version now includes X-ray heating. Revised version accepted for publication in Phys. Rev. D

References in corpus (29)

• Planck 2015 results. XIII. Cosmological parameters
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• An absorption profile centred at 78 megahertz in the sky-averaged spectrum
• A New Calculation of the Recombination Epoch
• Possible interaction between baryons and dark-matter particles revealed by the first stars
• How exactly did the Universe become neutral?
• ARCADE 2 Measurement of the Extra-Galactic Sky Temperature at 3-90 GHz
• The Global 21 Centimeter Background from High Redshifts
• Insights on Dark Matter from Hydrogen during Cosmic Dawn
• 21 cm fluctuations from inhomogeneous X-ray heating before reionization
• Enhanced global signal of neutral hydrogen due to excess radiation at cosmic dawn
• Concerns about Modelling of the EDGES Data
• Early-Universe Constraints on Dark Matter-Baryon Scattering and their Implications for a Global 21cm Signal
• Reionization by Hard Photons: I. X-rays from the First Star Clusters
• What does the first highly-redshifted 21-cm detection tell us about early galaxies?
• Constraining Baryon--Dark Matter Scattering with the Cosmic Dawn 21-cm Signal
• New Physics in the Rayleigh-Jeans Tail of the CMB
• Heating of Baryons due to Scattering with Dark Matter During the Dark Ages
• The EDGES 21 cm Anomaly and Properties of Dark Matter
• The Radio Background Below 100 MHz
• The Effects of Dark Matter-Baryon Scattering on Redshifted 21 cm Signals
• Bounds on Dark Matter annihilations from 21 cm data
• A new light on 21 cm intensity fluctuations from the dark ages
• Is there an unaccounted excess Extragalactic Cosmic Radio Background?
• Primordial magnetic fields and the HI signal from the epoch of reionization
• Baryon-Dark matter interaction in presence of magnetic fields in light of EDGES signal
• Primordial magnetic fields during the cosmic dawn in light of EDGES 21-cm signal
• Hydrogen spin oscillations in a background of axions and the 21-cm brightness temperature
• Impact of inhomogeneous CMB heating of gas on the HI 21-cm signal during dark ages

Cited by in corpus (5)

• Lyman-$\alpha$ coupling and heating at Cosmic Dawn
• Probing Interacting Dark Energy and Scattering of Baryons with Dark Matter in Light of EDGES 21cm Signal
• Primordial magnetic fields during the cosmic dawn in light of EDGES 21-cm signal
• Impact of cosmic rays on the global 21-cm signal during cosmic dawn
• Large HI optical depth and Redshifted 21-cm signal from cosmic dawn