Reconstructing the Nature of the First Cosmic Sources from the Anisotropic 21-cm Signal

Fialkov, Anastasia; Barkana, Rennan; Cohen, Aviad

doi:10.1103/physrevlett.114.101303

Cited by 34 publications

(43 citation statements)

References 30 publications

(39 reference statements)

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“…Neutral hydrogen is all-pervasive until its (re)ionization completes and it complements (i.e. anti-correlates) with sources of ionization, with the CMB and with the IR/X-ray background (although see Fialkov et al, 2015). Moreover due to the line-nature of the 21-cm hyperfine transition, redshift (and velocity) information can be gained directly from 21-cm emission by fine-tuning observations to different radio frequencies [i.e.…”

Section: Current Constraints On the Cosmic Dawn And Epoch Of Reionizamentioning

confidence: 99%

“…To first order, the power-spectrum is isotropic and can be spherically averaged (where the frequency direction over some limited bandwidth is a proxy for comoving distance, hence inverse wavenumber), although in the case of SKA (possibly even before) the sensitivity if sufficient to measure anisotropy in the power-spectrum which can be an exciting measure of underlying physics (e.g. Fialkov et al, 2015). Hence it is often better to express the power-spectrum in two dimensions, separating the wave vector in a component perpendicular to the line of sight and a component parallel to it, in particular to study peculiar velocities, the light-cone effect, as well as potentially identify still-remaining systematic errors in the data-processing.…”

Section: Pos(aaska14)001mentioning

confidence: 99%

See 1 more Smart Citation

The Cosmic Dawn and Epoch of Reionisation with SKA

Koopmans¹,

Pritchard²,

Mellema³

et al. 2015

Proceedings of Advancing Astrophysics With the Square Kilometre Array — PoS(AASKA14)

109

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Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-α emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from z ∼6-200 for astrophysical and cosmological studies, opening not only the Epoch of Reionization, but also its preceding Cosmic Dawn (z ∼30-15) and possibly even the later phases of the Dark Ages (z ∼200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the Epoch of Reionization, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array (SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range z ∼6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume. This is done within the framework of the current SKA1 baseline design and a nominal CD/EoR straw-man survey, consisting of a shallow, medium-deep and deep survey, the latter probing down to ∼1 mK brightness temperature on arc-minute scales at the end of reionization. Possible minor modifications to the design of SKA1 and the upgrade to SKA2 are discussed, in addition to science that could be done already during roll-out when SKA1 still has limited capabilities and/or core collecting area.Advancing Astrophysics with the Square Kilometre Array

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Section: Current Constraints On the Cosmic Dawn And Epoch Of Reionizamentioning

confidence: 99%

Section: Pos(aaska14)001mentioning

confidence: 99%

The Cosmic Dawn and Epoch of Reionisation with SKA

Koopmans¹,

Pritchard²,

Mellema³

et al. 2015

Proceedings of Advancing Astrophysics With the Square Kilometre Array — PoS(AASKA14)

109

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show abstract

“…Based on several theoretical models the cosmological Global 21cm signal changes its shape and amplitude as a function of redshifted frequencies. Fialkov et al (2014Fialkov et al ( , 2015; Cohen et al (2017) have used a semi-numerical approach to model possible 21cm Global signals in the redshift range, z ∼ 6−40, and is flexible to explore the large dynamical range of astrophysical parameters. Parameterization of the cosmological signal has been done using physical parameters which are directly related to the IGM properties, from which we can infer the physics of the earliest sources.…”

Section: Simulating the Global Signalmentioning

confidence: 99%

Extracting the 21cm Global Signal using Artificial Neural Networks

Choudhury

Datta

Chakraborty

2019

Monthly Notices of the Royal Astronomical Society

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The study of the cosmic Dark Ages, Cosmic Dawn, and Epoch of Reionization (EoR) using the all-sky averaged redshifted HI 21cm signal, are some of the key science goals of most of the ongoing or upcoming experiments, for example, EDGES, SARAS, and the SKA. This signal can be detected by averaging over the entire sky, using a single radio telescope, in the form of a Global signal as a function of only redshifted HI 21cm frequencies. One of the major challenges faced while detecting this signal is the dominating, bright foreground. The success of such detection lies in the accuracy of the foreground removal. The presence of instrumental gain fluctuations, chromatic primary beam, radio frequency interference (RFI) and the Earth's ionosphere corrupts any observation of radio signals from the Earth. Here, we propose the use of Artificial Neural Networks (ANN) to extract the faint redshifted 21cm Global signal buried in a sea of bright Galactic foregrounds and contaminated by different instrumental models. The most striking advantage of using ANN is the fact that, when the corrupted signal is fed into a trained network, we can simultaneously extract the signal as well as foreground parameters very accurately. Our results show that ANN can detect the Global signal with 92% accuracy even in cases of mock observations where the instrument has some residual time-varying gain across the spectrum.

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“…Recently, Fialkov et al (2015) [130] reconsidered the anisotropic 21-cm power spectrum using a semi-numerical simulation that covered a wide period of early cosmic history. Focusing on the dominant anisotropic term (P µ 2 ), they showed that the anisotropy is large and thus potentially measurable at most redshifts, and it acts as a model-independent cosmic clock that tracks the evolution of 21-cm fluctuations over various eras (see Figure 13).…”

Section: Anisotropy Of the 21-cm Signalmentioning

confidence: 99%

“…Indeed, a clear observational indication that this feature corresponds to a cosmic milestone is that the minima at all k > 0.5 Mpc −1 should occur at essentially the same redshift (namely the true redshift of the heating transition); lower wavenumbers correspond to larger scales than the typical X-ray mean free path, leading to a more complicated evolution and to minima delayed to lower redshifts (see also Figure 41). More generally, observations of the 21-cm power spectrum over a broad range of wavenumbers will clearly probe the X-ray spectrum of the sources of cosmic heating [92,260,261,130].…”

Section: Late Heating and Reionizationmentioning

confidence: 99%

The rise of the first stars: Supersonic streaming, radiative feedback, and 21-cm cosmology

Barkana

2016

Physics Reports

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111

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Understanding the formation and evolution of the first stars and galaxies represents one of the most exciting frontiers in astronomy. Since the universe was filled with hydrogen atoms at early times, the most promising method for observing the epoch of the first stars is to use the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on the cosmic reionization era, but observations of the pre-reionization cosmic dawn are also beginning and promise exciting discoveries. While observationally unexplored, theoretical studies predict a rich variety of observational signatures from the astrophysics of the early galaxies that formed during cosmic dawn. As the first stars formed, their radiation (plus that from stellar remnants) produced feedback that radically affected both the intergalactic medium and the character of newly-forming stars. Lyman-α radiation from stars generated a strong 21-cm absorption signal, observation of which is currently the only feasible method of detecting the dominant population of galaxies at redshifts as early as z ∼ 25. Another major player is cosmic heating; if due to soft X-rays, then it occurred fairly early (z ∼ 15) and produced the strongest pre-reionization signal, while if it is due to hard X-rays, as now seems more likely, then it occurred later and may have dramatically affected the 21-cm sky even during reionization. In terms of analysis, much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations, a rich dataset that can be used to reconstruct the astrophysical information of greatest interest. This does not, however, diminish the importance of finding additional probes that are complementary or amenable to a more model-independent analysis. Examples include the global (sky-averaged) 21-cm spectrum, and the line-of-sight anisotropy of the 21-cm power spectrum. Another striking feature may result from a recently recognized effect of a supersonic relative velocity between the dark matter and gas. This effect enhanced large-scale clustering and, if early 21-cm fluctuations were dominated by small galactic halos, it produced a prominent pattern on 100 Mpc scales. Work in this field, focused on understanding the whole era of reionization and cosmic dawn with analytical models and numerical simulations, is likely to grow in intensity and importance, as the theoretical predictions are finally expected to confront 21-cm observations in the coming years.

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Reconstructing the Nature of the First Cosmic Sources from the Anisotropic 21-cm Signal

Cited by 34 publications

References 30 publications

The Cosmic Dawn and Epoch of Reionisation with SKA

The Cosmic Dawn and Epoch of Reionisation with SKA

Extracting the 21cm Global Signal using Artificial Neural Networks

The rise of the first stars: Supersonic streaming, radiative feedback, and 21-cm cosmology

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