Moench, G. L.: Methods of Examining Sterile Couples

Greenhill, J.P.

doi:10.1016/s0002-9378(15)31142-x

Cited by 4 publications

(4 citation statements)

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“…These wide-beam experiments should detect the onset of X-ray heating through the global brightness temperature evolution (see Fig. 9), provided that foregrounds are removed to the level of ∼tens of mK (Greenhill & Bernardi 2012).…”

Section: Discussionmentioning

confidence: 99%

Signatures of X-rays in the early Universe

Mesinger

Ferrara

Spiegel

2013

Monthly Notices of the Royal Astronomical Society

229

317

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With their long mean free paths and efficient heating of the intergalactic medium (IGM), X-rays could have a dramatic impact on the thermal and ionization history of the Universe. Here we run several semi-numeric simulations of the Dark Ages and the Epoch of Reionization (EoR), including both X-rays and UV radiation fields, attempting to provide an intuitive framework for interpreting upcoming observations. We explore the impact of X-rays on various signals: (i) Reionization history: including X-rays results in an earlier, slightly more extended EoR. However, efficient thermal feedback from X-ray heating could yield an extended epoch in which the Universe was ≈ 10% ionized. (ii) Reionization morphology: a sizable (∼10%) contribution of X-rays to reionization results in a more uniform morphology, though the impact is modest when compared at the same global neutral fraction,x HI . Specifically, X-rays produce a dearth of fully neutral regions and a suppression of smallscale (k ∼ > 0.1Mpc −1 ) ionization power by a factor of ∼ < 2. However, these changes in morphology cannot be countered by increasing the bias of the ionizing sources, making them a robust indicator of an X-ray contribution to the EoR. (iii) The kinetic Sunyaev-Zel'dovich (kSZ) effect: at a fixed reionization history, X-rays decrease the kSZ power at l = 3000 by ≈ 0.5µK 2 . Our extreme model in which X-rays entirely drive reionization is the only one which is marginally consistent with the recent upper limits on this signal from the South Pole Telescope, assuming no thermal Sunyaev-Zel'dovich (tSZ) -dusty galaxy cross-correlation. Since this extreme model is unlikely, we conclude that there should be a sizable tSZ-dusty galaxy cross-correlation. (iv) The redshifted 21cm signal: the impact of X-rays on the 21cm power spectrum during the advanced stages of reionization (x HI ∼ < 0.7) is modest, except in extreme, X-ray dominated models. The largest impact of X-rays is to govern the timing and duration of IGM heating. In fact, unless thermal feedback is efficient, the epoch of X-ray heating likely overlaps with the beginning of reionization. This results in a 21cm power spectrum which is ∼10-100 times higher atx HI ∼ > 0.9 than obtained from naive estimates ignoring this overlap. On the other hand, if thermal feedback is efficient, the resulting extended epoch between X-ray heating and reionization could provide a clean probe of the matter power spectrum in emission, at redshifts more accessible than the Dark Ages.

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Section: Discussionmentioning

confidence: 99%

Signatures of X-rays in the early Universe

Mesinger

Ferrara

Spiegel

2013

Monthly Notices of the Royal Astronomical Society

229

317

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“…Several ground-based experiments are underway (e.g. ; EDGES, SCI-HI, LEDA, BIGHORNS; Bowman & Rogers 2010;Voytek et al 2014;Greenhill & Bernardi 2012;Sokolowski et al 2015), though space-based observatories will be required to probe the cosmic dawn at z 30 (e.g., the Dark Ages Radio Explorer, (DARE); Burns et al 2012), as the Earth's ionosphere reflects and refracts radio signals at low frequencies (Vedantham et al 2013;Datta et al 2014). Interferometers are in principle capable of measuring the global 21-cm signal, so long as they are compact (Presley et al 2015;Singh et al 2015) or can overcome challenges in lunar occultation techniques (Vedantham et al 2014).…”

Section: Introductionmentioning

confidence: 99%

INTERPRETING THE GLOBAL 21-cm SIGNAL FROM HIGH REDSHIFTS. II. PARAMETER ESTIMATION FOR MODELS OF GALAXY FORMATION

Mirocha

Harker

Burns

2015

ApJ

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Following our previous work, which related generic features in the sky-averaged (global) 21-cm signal to properties of the intergalactic medium, we now investigate the prospects for constraining a simple galaxy formation model with current and near-future experiments. Markov-Chain Monte Carlo fits to our synthetic dataset, which includes a realistic galactic foreground, a plausible model for the signal, and noise consistent with 100 hours of integration by an ideal instrument, suggest that a simple four-parameter model that links the production rate of Lyman-α, Lyman-continuum, and X-ray photons to the growth rate of dark matter halos can be well-constrained (to ∼ 0.1 dex in each dimension) so long as all three spectral features expected to occur between 40 ν/MHz 120 are detected. Several important conclusions follow naturally from this basic numerical result, namely that measurements of the global 21-cm signal can in principle (i) identify the characteristic halo mass threshold for star formation at all redshifts z 15, (ii) extend z 4 upper limits on the normalization of the X-ray luminosity star-formation rate (L X -SFR) relation out to z ∼ 20, and (iii) provide joint constraints on stellar spectra and the escape fraction of ionizing radiation at z ∼ 12. Though our approach is general, the importance of a broad-band measurement renders our findings most relevant to the proposed Dark Ages Radio Explorer, which will have a clean view of the global 21-cm signal from ∼ 40 − 120 MHz from its vantage point above the radio-quiet, ionosphere-free lunar far-side.

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“…This is a concern for some instruments, since the principles of aperture synthesis and coherent integration with interferometers rely on the constancy of the radio sky throughout the integration. However, instruments such as the MWA and LEDA (Greenhill & Bernardi 2012) will implement snapshot imaging with subsequent combination in the image domain, an approach that might be made robust to this kind of variability.…”

Section: Discussionmentioning

confidence: 99%

Low-Frequency Observations of the Moon With the Murchison Widefield Array

McKinley

Briggs

Kaplan

et al. 2012

The Astronomical Journal

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A new generation of low frequency radio telescopes is seeking to observe the redshifted 21 cm signal from the Epoch of Reionization (EoR), requiring innovative methods of calibration and imaging to overcome the difficulties of widefield -2low frequency radio interferometry. Precise calibration will be required to separate the small expected EoR signal from the strong foreground emission at the frequencies of interest between 80 and 300 MHz. The Moon may be useful as a calibration source for detection of the EoR signature, as it should have a smooth and predictable thermal spectrum across the frequency band of interest. Initial observations of the Moon with the Murchison Widefield Array 32 tile prototype show that the Moon does exhibit a similar trend to that expected for a cool thermally emitting body in the observed frequency range, but that the spectrum is corrupted by reflected radio emission from Earth. In particular, there is an abrupt increase in the observed flux density of the Moon within the internationally recognised Frequency Modulated (FM) radio band. The observations have implications for future low frequency surveys and EoR detection experiments that will need to take this reflected emission from the Moon into account. The results also allow us to estimate the equivalent isotropic power emitted by the Earth in the FM band and to determine how bright the Earth might appear at metre wavelengths to an observer beyond our own solar system.

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Moench, G. L.: Methods of Examining Sterile Couples

Cited by 4 publications

References 0 publications

Signatures of X-rays in the early Universe

Signatures of X-rays in the early Universe

INTERPRETING THE GLOBAL 21-cm SIGNAL FROM HIGH REDSHIFTS. II. PARAMETER ESTIMATION FOR MODELS OF GALAXY FORMATION

Low-Frequency Observations of the Moon With the Murchison Widefield Array

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