Large HI optical depth and Redshifted 21-cm signal from cosmic dawn

Abstract

The HI 21-cm optical depth (${\tau }_b$) can be considerably large as the kinetic and spin temperature of the inter-galactic medium (IGM) is expected to be very low during cosmic dawn. It will be particularly higher at regions with HI over-density. We revisit the validity of the widely used linearized equation for estimating the HI 21-cm differential brightness temperature ($T_b$) which assumes ${\tau }_b<<1$ and approximates $[1-\exp (-{\tau }_b)]$ as ${\tau }_b$. We consider two scenarios, one without any additional cooling mechanism or radio background (referred as the standard scenario) and the other (referred as the excess-cooling} scenario) assumes the EDGES-like absorption profile and an excess cooling mechanism. We find that given a measured global absorption signal, consistent with the standard (excess-cooling) scenario, the linearized equation overestimates the spin temperature by $\sim 5\%(10\%)$. Further, using numerical simulations, we study the impact that the large optical depth has on various signal statistics. We observe that the variance, skewness and kurtosis, calculated at simulation resolution ($\sim 0.5h^{-1}\mathrm{Mpc}$), are over-predicted up to $\sim 30\%$, $30\%$ and $15\%$ respectively for the standard and up to $\sim 90\%$, $50\%$ and $50\%$ respectively for the excess-cooling scenario. Moreover, we find that the probability distribution function of $T_b$ is squeezed and becomes more Gaussian in shape if no approximation is made. The spherically averaged HI power spectrum is overpredicted by up to $\sim 25\%$ and $80\%$ at all scales for the standard and excess-cooling scenarios respectively.

arXiv comment9 pages, 6 figures. Accepted for publication in the MNRAS

References in corpus (52)

• An absorption profile centred at 78 megahertz in the sky-averaged spectrum
• 21-cm cosmology
• Hydrogen Epoch of Reionization Array (HERA)
• Possible interaction between baryons and dark-matter particles revealed by the first stars
• How exactly did the Universe become neutral?
• Planck 2013 results. XVII. Gravitational lensing by large-scale structure
• Science with the Murchison Widefield Array
• Improved upper limits on the 21-cm signal power spectrum of neutral hydrogen at $\mathbf{z}\approx 9.1$ from LOFAR
• Upper limits on the 21-cm Epoch of Reionization power spectrum from one night with LOFAR
• Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal
• Deep multi-redshift limits on Epoch of Reionisation 21cm Power Spectra from Four Seasons of Murchison Widefield Array Observations
• A lower limit of dz > 0.06 for the duration of the reionization epoch
• The observable signature of late heating of the Universe during cosmic reionization
• Design and characterization of the Large-Aperture Experiment to Detect the Dark Age (LEDA) radiometer systems
• On using visibility correlations to probe the HI distribution from the dark ages to the present epoch I: Formalism and the expected signal
• Probing the Dark Ages at Z~20: The SCI-HI 21 cm All-Sky Spectrum Experiment
• The 21cm angular-power spectrum from the dark ages
• High Performance P3M N-body code: CUBEP3M
• Improving the Epoch of Reionization Power Spectrum Results from Murchison Widefield Array Season 1 Observations
• BIGHORNS - Broadband Instrument for Global HydrOgen ReioNisation Signal
• Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum
• 21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
• Light cone effect on the reionization 21-cm power spectrum
• Constraining the intergalactic medium at $z\approx$ 9.1 using LOFAR Epoch of Reionization observations
• Fast Large-Scale Reionization Simulations
• SARAS 2 constraints on global 21-cm signals from the Epoch of Reionization
• 21-cm Fluctuations from Charged Dark Matter
• Tight Constraints on the Excess Radio Background at $z=9.1$ from LOFAR
• High-redshift radio galaxies: a potential new source of 21-cm fluctuations
• Interpreting LOFAR 21-cm signal upper limits at z~9.1 in the context of high-z galaxy and reionisation observations
• The subtlety of Ly-a photons: changing the expected range of the 21-cm signal
• The Epoch of Reionization
• Imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA
• Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case
• Constraining the state of the intergalactic medium during the Epoch of Reionization using MWA 21-cm signal observations
• Detection and extraction of signals from the epoch of reionization using higher order one-point statistics
• 21-cm signal from cosmic dawn - II: Imprints of the light-cone effects
• SARAS measurement of the Radio Background at long wavelengths
• Prediction of the 21-cm signal from reionization: comparison between 3D and 1D radiative transfer schemes
• Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn
• HI Epoch of Reionization Arrays
• Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn
• Impact of Ly$\alpha$ heating on the global 21-cm signal from the Cosmic Dawn
• Redshifted 21-cm bispectrum II: Impact of the spin temperature fluctuations and redshift space distortions on the signal from the Cosmic Dawn
• Prospects of constraining reionization model parameters using Minkowski tensors and Betti numbers
• Demonstrating the Tapered Gridded Estimator (TGE) for the Cosmological HI 21-cm Power Spectrum using $150\mathrm{MHz}$ GMRT observations
• All sky angular power spectrum: I. Estimating brightness temperature fluctuations using TGSS 150 MHz survey
• First multi-redshift limits on post-Epoch of Reionization (post-EoR) 21 cm signal from z = 1.96 - 3.58 using uGMRT
• Extracting the 21 cm EoR signal using MWA drift scan data
• Cosmological implications of the composite spectra of galactic X-ray binaries constructed using MAXI data
• Maximum amplitude of the high-redshift 21-cm absorption feature
• Cosmic recombination history in light of EDGES measurements of the cosmic dawn 21-cm signal

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• PINION: Physics-informed neural network for accelerating radiative transfer simulations for cosmic reionization
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• The Effect of Large Optical Depths on the Non-Gaussian 21-cm signal from Cosmic Dawn