First Results on the Epoch of Reionization from First Light with SARAS 2

Singh, Saurabh; Subrahmanyan, R.; Shankar, N. Udaya; Rao, Mayuri Sathyanarayana; Fialkov, Anastasia; Cohen, Aviad; Barkana, Rennan; Girish, B. S.; Raghunathan, A.; Somashekar, R.K.; Srivani, K. S.

doi:10.3847/2041-8213/aa831b

Cited by 139 publications

(120 citation statements)

References 48 publications

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“…To produce this set of models, ΛCDM cosmology was assumed and the following astrophysical parameters were varied in the broadest range allowed by observations: f * , V c , f X , τ and R mfp ; in addition, hard versus soft X-ray SEDs were explored. Earlier, 25 models out of this set, sharing low X-ray efficiency (f X = 0 or f X = 0.1) and rapid reionization, were found inconsistent with SARAS 2 data in the 110-200 MHz frequency range (Singh et al 2017;Singh et al 2018). Extending the dataset of astrophysical models and varying, in addition to the above-mentioned parameters, the slope of the X-ray spectrum and the minimum frequency of X-ray photons, a larger set of models was produced and examined with the EDGES high-band data (Cohen et al in prep.…”

Section: Discussionmentioning

confidence: 57%

The Redshifted 21 cm Signal in the EDGES Low-band Spectrum

Singh

Subrahmanyan

2019

ApJ

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141

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The EDGES collaboration reported the finding of an unexpectedly deep absorption in the radio background at 78 MHz and interpreted the dip as a first detection of redshifted 21-cm from Cosmic Dawn. We have attempted an alternate analysis, adopting a maximally smooth function approach to model the foreground. A joint fit to the spectrum using such a function together with a flattened absorption profile yields a best fit absorption amplitude of 921 ± 35 mK. The depth of the 21-cm absorption inferred by the EDGES analysis required invoking non-standard cosmology or new physics or new sources at Cosmic Dawn and this tension with accepted models is compounded by our analysis that suggests absorption of greater depth. Alternatively, the measured spectrum may be equally-well fit assuming that there exists a residual unmodeled systematic sinusoidal feature and we explore this possibility further by examining for any additional 21-cm signal. The data then favors an absorption with Gaussian model parameters of amplitude 133 ± 60 mK, best width at half-power 9 ± 3 MHz and center frequency 72.5 ± 0.8 MHz. We also examine the consistency of the measured spectrum with plausible redshifted 21-cm models: a set of 3 of the 265 profiles in the global 21-cm atlas of Cohen et al. (2017) are favored by the spectrum. We conclude that the EDGES data may be consistent with standard cosmology and astrophysics, without invoking excess radio backgrounds or baryon-dark matter interactions.

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Section: Discussionmentioning

confidence: 57%

The Redshifted 21 cm Signal in the EDGES Low-band Spectrum

Singh

Subrahmanyan

2019

ApJ

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141

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“…Besides estimating the change ∆P Lyα (k, z) in Lymanα forest power spectrum due to reionization effects, we consider how 21 cm observations could be used to predict ∆P(k, z) and mitigate this systematic effect. The H i 21 cm hyperfine transition is a potentially powerful probe of reionization, and global measurements of the signal have already ruled out some models (Monsalve et al 2017;Singh et al 2017Singh et al , 2018. We find that there is a quantitative relation between ∆P Lyα (k, z) and the full history of the cross-correlation of the matter and the ionization fraction.…”

Section: Introductionmentioning

confidence: 65%

Impact of inhomogeneous reionization on the Lyman-α forest

Montero-Camacho

Hirata

Martini

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The Lyman-α forest at high redshifts is a powerful probe of reionization. Modeling and observing this imprint comes with significant technical challenges: inhomogeneous reionization must be taken into account while simultaneously being able to resolve the web-like small-scale structure prior to reionization. In this work we quantify the impact of inhomogeneous reionization on the Lyman-α forest at lower redshifts (2 < z < 4), where upcoming surveys such as DESI will enable precision measurements of the flux power spectrum. We use both small box simulations capable of handling the small-scale structure of the Lyman-α forest and semi-numerical large box simulations capable of representing the effects of inhomogeneous reionization. We find that inhomogeneous reionization could produce a measurable effect on the Lyman-α forest power spectrum. The deviation in the 3D power spectrum at z obs = 4 and k = 0.14 Mpc −1 ranges from 19 -36%, with a larger effect for later reionization. The corrections decrease to 2.0 -4.1% by z obs = 2. The impact on the 1D power spectrum is smaller, and ranges from 3.3 -6.5% at z obs = 4 to 0.35 -0.75% at z obs = 2, values which are comparable to the statistical uncertainties in current and upcoming surveys. Furthermore, we study how can this systematic be constrained with the help of the quadrupole of the 21 cm power spectrum.1 More precisely, the optical depth is proportional to the neutral hydrogen density, which in turn depends on the density and temperature of the gas and the photoionization rate. This is then smeared by the Doppler width of the Lyman-α line.

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“…A number of observational programs are currently underway, or have recently been completed that aimed to detect the 21cm brightness temperature from the EoR and CD. The 21cm global experiments, such as EDGES 1 (Bowman et al 2018) or SARAS 2 (Singh et al 2017) aim to measure the sky-averaged spectrum of the 21-cm signal. The tentative detection of the global 21-cm signal reported by the EDGES team (Bowman et al 2018) has unexpected properties.…”

Section: Introductionmentioning

confidence: 99%

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

Mertens

Mevius

Koopmans

et al. 2020

Monthly Notices of the Royal Astronomical Society

292

274

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A new upper limit on the 21-cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 hours of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally-smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally-weighted power spectrum inference. Previously seen 'excess power' due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25 − 0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-σ upper limit of ∆ 2 21 < (73) 2 mK 2 at k = 0.075 h cMpc −1 is found, an improvement by a factor ≈ 8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radio-frequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.

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First Results on the Epoch of Reionization from First Light with SARAS 2

Cited by 139 publications

References 48 publications

The Redshifted 21 cm Signal in the EDGES Low-band Spectrum

The Redshifted 21 cm Signal in the EDGES Low-band Spectrum

Impact of inhomogeneous reionization on the Lyman-α forest

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

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