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• 1
Article
Language: English
In: Monthly Notices of the Royal Astronomical Society, 06/11/2018, Vol.477(1), pp.864-866
Keywords: Meteorology & Climatology ; Astronomy & Astrophysics;
ISSN: 0035-8711
E-ISSN: 1365-2966
Source: Oxford University Press (via CrossRef)
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• 2
Article
In: Monthly Notices of the Royal Astronomical Society, 2017, Vol. 474(4), pp.4487-4499
Description: We present a baseline sensitivity analysis of the Hydrogen Epoch of Reionization Array (HERA) and its build-out stages to one-point statistics (variance, skewness, and kurtosis) of redshifted 21 cm intensity fluctuation from the Epoch of Reionization (EoR) based on realistic mock observations. By developing a full-sky 21 cm light-cone model, taking into account the proper field of view and frequency bandwidth, utilizing a realistic measurement scheme, and assuming perfect foreground removal, we show that HERA will be able to recover statistics of the sky model with high sensitivity by averaging over measurements from multiple fields. All build-out stages will be able to detect variance, while skewness and kurtosis should be detectable for HERA128 and larger. We identify sample variance as the limiting constraint of the measurements at the end of reionization. The sensitivity can also be further improved by performing frequency windowing. In addition, we find that strong sample variance fluctuation in the kurtosis measured from an individual field of observation indicates the presence of outlying cold or hot regions in the underlying fluctuations, a feature that can potentially be used as an EoR bubble indicator.
Keywords: Methods: Statistical ; Dark Ages, Reionization, First Stars ; Cosmology: Observations
ISSN: 0035-8711
E-ISSN: 1365-2966
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• 3
Article
In: The Astrophysical Journal, 09/20/2017, Vol.847(1), p.64
Description: We report constraints on the global $21$ cm signal due to neutral hydrogen at redshifts $14.8 \geq z \geq 6.5$. We derive our constraints from low foreground observations of the average sky brightness spectrum conducted with the EDGES High-Band instrument between September $7$ and October $26$, $2015$. Observations were calibrated by accounting for the effects of antenna beam chromaticity, antenna and ground losses, signal reflections, and receiver parameters. We evaluate the consistency between the spectrum and phenomenological models for the global $21$ cm signal. For tanh-based representations of the ionization history during the epoch of reionization, we rule out, at $\geq2\sigma$ significance, models with duration of up to $\Delta z = 1$ at $z\approx8.5$ and higher than $\Delta z = 0.4$ across most of the observed redshift range under the usual assumption that the $21$ cm spin temperature is much larger than the temperature of the cosmic microwave background (CMB) during reionization. We also investigate a `cold' IGM scenario that assumes perfect Ly$\alpha$ coupling of the $21$ cm spin temperature to the temperature of the intergalactic medium (IGM), but that the IGM is not heated by early stars or stellar remants. Under this assumption, we reject tanh-based reionization models of duration $\Delta z \lesssim 2$ over most of the observed redshift range. Finally, we explore and reject a broad range of Gaussian models for the $21$ cm absorption feature expected in the First Light era. As an example, we reject $100$ mK Gaussians with duration (full width at half maximum) $\Delta z \leq 4$ over the range $14.2\geq z\geq 6.5$ at $\geq2\sigma$ significance.
Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Instrumentation And Methods For Astrophysics;
ISSN: The Astrophysical Journal
ISSN: 0004637X
E-ISSN: 1538-4357
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• 4
Article
Language: English
In: The Astrophysical Journal, 2018, Vol.863(1), p.11 (11pp)
Description: We use the sky-average spectrum measured by EDGES High-band (90–190 MHz) to constrain parameters of early galaxies independent of the absorption feature at 78 MHz reported by Bowman et al. These parameters represent traditional models of cosmic dawn and the epoch of reionization produced with the 21cmFAST simulation code. The parameters considered are (1) the UV ionizing efficiency ( ζ ); (2) minimum halo virial temperature hosting efficient star-forming galaxies ( ); (3) integrated soft-band X-ray luminosity ( ); and (4) minimum X-ray energy escaping the first galaxies ( E 0 ), corresponding to a typical H i column density for attenuation through the interstellar medium. The High-band spectrum disfavors high values of and ζ , which correspond to signals with late absorption troughs and sharp reionization transitions. It also disfavors intermediate values of , which produce relatively deep and narrow troughs within the band. Specifically, we rule out (95% C.L.). We then combine the EDGES High-band data with constraints on the electron-scattering optical depth from Planck and the hydrogen neutral fraction from high- z quasars. This produces a lower degeneracy between ζ and than that reported by Greig & Mesinger using the Planck and quasar constraints alone. Our main result in this combined analysis is the estimate (95% C.L.). We leave the evaluation of 21 cm models using simultaneously data from EDGES Low- and High-band for future work.
Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Astrophysics Of Galaxies;
ISSN: 0004-637X
E-ISSN: 1538-4357
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• 5
Article
Language: English
In: The Astrophysical Journal, 2006, Vol.648(2), pp.767-773
Description: Statistical observations of the epoch of reionization using the 21 cm line of neutral hydrogen have the potential to revolutionize our understanding of structure formation and the first luminous objects. However, these observations are complicated by a host of strong foreground sources. Several foreground-removal techniques have been proposed in the literature, and it has been assumed that these would be used in combination to reveal the epoch of reionization (EOR) signal. By studying the characteristic subtraction errors of the proposed foreground-removal techniques, we identify an additional subtraction stage that can further reduce the EOR foreground contamination, and study the interactions between the foreground-removal algorithms. This enables us to outline a comprehensive foreground-removal strategy that incorporates all previously proposed subtraction techniques. Using this foreground-removal framework and the characteristic subtraction errors, we discuss the complementarity of different foreground-removal techniques and the implications for array design and the analysis of EOR data.
Keywords: Astrophysics;
ISSN: 0004-637X
E-ISSN: 1538-4357
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• 6
Article
Language: English
In: The Astrophysical Journal, 2014, Vol.793(1), p.28 (13pp)
Description: Detection of the epoch of reionization (EoR) in the redshifted 21 cm line is a challenging task. Here, we formulate the detection of the EoR signal using the drift scan strategy. This method potentially has better instrumental stability compared to the case where a single patch of sky is tracked. We demonstrate that the correlation time between measured visibilities could extend up to 1-2 hr for an interferometer array such as the Murchison Widefield Array, which has a wide primary beam. We estimate the EoR power based on a cross-correlation of visibilities over time and show that the drift scan strategy is capable of detecting the EoR signal with a signal to noise that is comparable/better compared to the tracking case. We also estimate the visibility correlation for a set of bright point sources and argue that the statistical inhomogeneity of bright point sources might allow their separation from the EoR signal.
Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics;
ISSN: 0004-637X
E-ISSN: 1538-4357
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• 7
Article
Language: English
In: The Astrophysical Journal Letters, 2015, Vol.807(2), p.L28 (5pp)
Description: We confirm our recent prediction of the “pitchfork” foreground signature in power spectra of high-redshift 21 cm measurements where the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be the most sensitive to the cosmological H i signal. In our recent paper, many signatures from the simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data, but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through the coherent averaging of 12 independent snapshots with identical instrument settings and provide the first confirmation of the prediction with a signal-to-noise ratio . This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures that have been proposed for future instruments such as the Hydrogen Epoch of Reionization Array and the Square Kilometre Array indicate they should suppress foreground leakage from the pitchfork by ∼40 dB relative to the MWA and significantly increase the likelihood of cosmological signal detection in these critical Fourier modes in the three-dimensional power spectrum.
Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Instrumentation And Methods For Astrophysics;
ISSN: 2041-8205
E-ISSN: 2041-8213
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• 8
Article
Language: English
In: The Astrophysical Journal, 2016, Vol.833(2), p.213 (16pp)
Description: The detection of redshifted 21 cm emission from the epoch of reionization (EoR) is a challenging task owing to strong foregrounds that dominate the signal. In this paper, we propose a general method, based on the delay spectrum approach, to extract H i power spectra that are applicable to tracking observations using an imaging radio interferometer ("Delay Spectrum with Imaging Arrays"). Our method is based on modeling the H i signal taking into account the impact of wide field effects such as the w -term, which are then used as appropriate weights in cross-correlating the measured visibilities. Our method is applicable to any radio interferometer that tracks a phase center and could be utilized for arrays such as the Murchison Widefield Array (MWA), Low Frequency Array (LOFAR), Giant Meterwave Radio Telescope (GMRT), Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), and HERA. In the literature the delay spectrum approach has been implemented for near-redundant baselines using drift scan observations. In this paper we explore the scheme for non-redundant tracking arrays. This is the first application of delay spectrum methodology to such data to extract the H i signal. We analyze 3 hr of MWA tracking data on the EoR1 field. We present both two-dimensional ( ) and one-dimensional (k) power spectra from the analysis. Our results are in agreement with the findings of other pipelines developed to analyze the MWA EoR data.
Keywords: Astronomy & Astrophysics ; Physics;
ISSN: 0004-637X
E-ISSN: 1538-4357
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• 9
Article
Language: English
In: The Astrophysical Journal, 2016, Vol.833(1), p.102 (19pp)
Description: The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques, such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two-dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hours of MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of mK 2 at k = 0.27 h Mpc −1 and z = 7.1, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis, we have identified a list of improvements to be made to our EoR data analysis strategies. These improvements will be implemented in the future and detailed in upcoming publications.
Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics;
ISSN: 0004-637X
E-ISSN: 1538-4357
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• 10
Article
Language: English
In: The Astrophysical Journal, 2015, Vol.804(1), p.14 (15pp)
Description: Detection of 21 cm emission of H i from the epoch of reionization, at redshifts , is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the H i signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic pitchfork signature on the “foreground wedge” in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor of ∼100 with negligible loss of sensitivity.
Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics;
ISSN: 0004-637X
E-ISSN: 1538-4357
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