scholarly journals The first power spectrum limit on the 21-cm signal of neutral hydrogen during the Cosmic Dawn at z = 20–25 from LOFAR

2019 ◽  
Vol 488 (3) ◽  
pp. 4271-4287 ◽  
Author(s):  
B K Gehlot ◽  
F G Mertens ◽  
L V E Koopmans ◽  
M A Brentjens ◽  
S Zaroubi ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Neutral Hydrogen ◽  
Hyperfine Line ◽  
The North ◽  
Upper Limits ◽  
Gain Errors ◽  
The Universe ◽  
Early Phases ◽  
Additional Variance ◽  
Spectrum Limit

ABSTRACT Observations of the redshifted 21-cm hyperfine line of neutral hydrogen from early phases of the Universe such as Cosmic Dawn and the Epoch of Reionization promise to open a new window onto the early formation of stars and galaxies. We present the first upper limits on the power spectrum of redshifted 21-cm brightness temperature fluctuations in the redshift range z = 19.8–25.2 (54–68 MHz frequency range) using 14 h of data obtained with the LOFAR-Low Band Antenna (LBA) array. We also demonstrate the application of a multiple pointing calibration technique to calibrate the LOFAR-LBA dual-pointing observations centred on the North Celestial Pole and the radio galaxy 3C220.3. We observe an unexplained excess of $\sim 30\!-\!50{{\ \rm per\ cent}}$ in Stokes / noise compared to Stokes V for the two observed fields, which decorrelates on ≳12 s and might have a physical origin. We show that enforcing smoothness of gain errors along frequency direction during calibration reduces the additional variance in Stokes I compared Stokes V introduced by the calibration on sub-band level. After subtraction of smooth foregrounds, we achieve a 2σ upper limit on the 21-cm power spectrum of $\Delta _{21}^2 \lt (14561\, \text{mK})^2$ at $k\sim 0.038\, h\, \text{cMpc}^{-1}$ and $\Delta _{21}^2 \lt (14886\, \text{mK})^2$ at $k\sim 0.038 \, h\, \text{cMpc}^{-1}$ for the 3C220 and NCP fields respectively and both upper limits are consistent with each other. The upper limits for the two fields are still dominated by systematics on most k modes.

scholarly journals Using strong gravitational lensing to probe the post-reionization H i power spectrum

2020 ◽  
Vol 498 (3) ◽  
pp. 3275-3282
Author(s):  
Urvashi Arora ◽  
Prasun Dutta
Keyword(s):  
Power Spectrum ◽  
Gravitational Lensing ◽  
Neutral Hydrogen ◽  
Point Sources ◽  
Dark Matter Halo ◽  
Strong Gravitational Lensing ◽  
The Galaxy ◽  
Formation And Evolution ◽  
The Universe ◽  
Expected Signal

ABSTRACT Probing statistical distribution of the neutral hydrogen (H i) using the redshifted 21-cm hyperfine-transition spectral line holds the key to understand the formation and evolution of the matter density in the Universe. The two-point statistics of the H i distribution can be estimated by measuring the power spectrum of the redshifted 21-cm signal using visibility correlation. A major challenge in this regard is that the expected signal is weak compared to the foreground contribution from the Galactic synchrotron emission and extragalactic point sources in the observing frequencies. In this work, we investigate the possibility of detecting the power spectrum of the redshifted 21-cm signal by using strong gravitational lensing of the galaxy clusters. This method has the advantage that it only enhances the H i signal and not the diffuse Galactic foreground. Based on four simple models of the cluster potentials, we show that the strong lenses at relatively lower redshifts with more than one dark matter halo significantly enhance the 21-cm signal from the post-reionization era. We discuss the merits and demerits of the method and the future studies required for further investigations.

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

2020 ◽  
Vol 493 (2) ◽  
pp. 1662-1685 ◽  
Author(s):  
F G Mertens ◽  
M Mevius ◽  
L V E Koopmans ◽  
A R Offringa ◽  
G Mellema ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Gaussian Process Regression ◽  
Spectral Structure ◽  
Signal Power ◽  
Spectral Correlation ◽  
Upper Limit ◽  
Upper Limits ◽  
Excess Power

ABSTRACT A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h 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 $\Delta ^2_{21} \lt (73)^2\, \mathrm{mK^2}$ at $k = 0.075\, \mathrm{h\, cMpc^{-1}}$ 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 radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.

scholarly journals Calibration requirements for epoch of reionization 21-cm signal observations – I. Effect of time-correlated gains

2020 ◽  
Vol 495 (4) ◽  
pp. 3683-3694
Author(s):  
Jais Kumar ◽  
Prasun Dutta ◽  
Nirupam Roy
Keyword(s):  
Power Spectrum ◽  
Dynamic Range ◽  
Neutral Hydrogen ◽  
High Dynamic Range ◽  
Time Correlation ◽  
Brightness Distribution ◽  
Gain Error ◽  
High Dynamic ◽  
Gain Errors ◽  
Compact Sources

ABSTRACT The residual gain errors add to the systematics of the radio interferometric observations. In case of the high dynamic range observations, these systematic effects dominates over the thermal noise of the observation. In this work, we investigate the effect of time-correlated residual gain errors in the estimation of the power spectrum of the sky brightness distribution in high dynamic range observations. Particularly, we discuss a methodology to estimate the bias in the power spectrum estimator of the redshifted 21-cm signal from neutral hydrogen in the presence of bright extragalactic compact sources. We find, that for the visibility-based power spectrum estimators, particularly those use nearby baseline correlations to avoid noise bias, the bias in the power spectrum arises mainly from the time correlation in the residual gain error. The bias also depends on the baseline distribution for a particular observation. Analytical calculations show that the bias is dominant for certain types of baseline pairs used for the visibility correlation. We perform simulated observation of extragalactic compact sources in the presence of residual gain errors with the Giant Metrewave Radio Telescope like array and estimate the bias in the power spectrum. Our results indicate that in order to estimate the redshifted 21-cm power spectrum, better calibration techniques, and estimator development are required.

scholarly journals Quantifying density-ionization correlations with the 21-cm power spectrum

2020 ◽  
Vol 498 (1) ◽  
pp. 373-384
Author(s):  
Michael Pagano ◽  
Adrian Liu
Keyword(s):  
Power Spectrum ◽  
Intergalactic Medium ◽  
Neutral Hydrogen ◽  
Upper Limits ◽  
Error Bars ◽  
Rule Out

ABSTRACT The epoch of reionization (EoR) – when neutral hydrogen in the intergalactic medium was systematically ionized – is a period in our Universe’s history that is currently poorly understood. However, a key prediction of most models is a correlation between the density and ionization field during the EoR. This has consequences for the 21-cm power spectrum. Here, we propose a parametrization for the density-ionization correlation and study the dependence of the 21-cm power spectrum on this parametrization. We use this formalism to forecast the ability of current and future observations to constrain these correlations. We find that upper limits on the dimensionless power spectrum at redshifts 7.5 < z < 8.5 using k bins between $0.1 \lt k \lt 0.75\, \textrm {Mpc}^{-1}$ with error bars at the level of ${\sim\! }20\, \textrm {mK}^2$ about our fiducial model would rule out uncorrelated reionization at $99{{\ \rm per\ cent}}$ credibility. Beyond upper limits, we find that at its full sensitivity, the Hydrogen Epoch of Reionization Array (HERA) will be able to place strong constraints on the sign and magnitude of density-ionization correlations.

scholarly journals Demonstrating the Tapered Gridded Estimator (TGE) for the Cosmological HI 21-cm Power Spectrum using 150 MHz GMRT observations

2020 ◽  
Author(s):  
Srijita Pal ◽  
Somnath Bharadwaj ◽  
Abhik Ghosh ◽  
Samir Choudhuri
Keyword(s):  
Power Spectrum ◽  
Unbiased Estimate ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Statistical Error ◽  
Temperature Fluctuations ◽  
Radio Frequency Interference ◽  
Rectangular Region ◽  
Angular Power Spectrum ◽  
The Mean

Abstract We apply the Tapered Gridded Estimator (TGE) for estimating the cosmological 21-cm power spectrum from 150 MHz GMRT observations which corresponds to the neutral hydrogen (HI) at redshift z = 8.28. Here TGE is used to measure the Multi-frequency Angular Power Spectrum (MAPS) Cℓ(Δν) first, from which we estimate the 21-cm power spectrum P(k⊥, k∥). The data here are much too small for a detection, and the aim is to demonstrate the capabilities of the estimator. We find that the estimated power spectrum is consistent with the expected foreground and noise behaviour. This demonstrates that this estimator correctly estimates the noise bias and subtracts this out to yield an unbiased estimate of the power spectrum. More than $47\%$ of the frequency channels had to be discarded from the data owing to radio-frequency interference, however the estimated power spectrum does not show any artifacts due to missing channels. Finally, we show that it is possible to suppress the foreground contribution by tapering the sky response at large angular separations from the phase center. We combine the k modes within a rectangular region in the ‘EoR window’ to obtain the spherically binned averaged dimensionless power spectra Δ2(k) along with the statistical error σ associated with the measured Δ2(k). The lowest k-bin yields Δ2(k) = (61.47)2 K2 at k = 1.59 Mpc−1, with σ = (27.40)2 K2. We obtain a 2 σ upper limit of (72.66)2 K2 on the mean squared HI 21-cm brightness temperature fluctuations at k = 1.59 Mpc−1.

Bismuth-bearing assemblages from the Northern Pennine Orefield

1996 ◽  
Vol 60 (399) ◽  
pp. 317-324 ◽  
Author(s):  
R. A. Ixer ◽  
B. Young ◽  
C. J. Stanley
Keyword(s):  
Qualitative Analysis ◽  
Fine Grained ◽  
Quartz Veins ◽  
The North ◽  
Data Form ◽  
Form Part ◽  
Native Bismuth ◽  
Monoclinic Pyrrhotite ◽  
Early Phases ◽  
And Tungsten

AbstractBismuthinite-bearing quartz veins from the Alston Block of the North Pennine Orefield are all close to, or above, the Rookhope and Tynehead cupolas of the buried Weardale Granite. They are uniform in composition and paragenesis and are earlier than the main fluorite-baryte-galena-sphalerite mineralization of the orefield. Rhythmical crystallization of quartz, chalcopyrite and minor pyrite is followed by fluorite-quartz-chalcopyrite-minor sphalerite-altered pyrrhotite mineralization. Early tin-bearing (up to 0.29 wt.% Sn) chalcopyrite encloses trace amounts of bismuthinite (Bi2S3), synchysite (CaREE(CO3)F2), argentopentlandite (Ag(FeNi)8S8) (close to being stoichiometric), pyrrhotite, cubanite and cosalite (Pb2Bi2S5), while early pyrite carries monoclinic pyrrhotite (close to Fe7S8) and tungsten-bearing cassiterite (up to 1.03 wt.% WO3). Bismuthinite is macroscopically visible and is associated with native bismuth and small, fine-grained, spherical aggregates that qualitative analysis suggests may be cosalite crystals. Synchysite and more rarely monazite, xenotime and adularia are intergrown with bismuthinite. These mineralogical data form part of the basis for an increasing awareness of the contribution of the Weardale Granite to the early phases of mineralization in the Alston Block.

scholarly journals Imaging the disc rim and a moving close-in companion candidate in the pre-transitional disc of V1247 Orionis

2018 ◽  
Vol 621 ◽  
pp. A7 ◽  
Author(s):  
Matthew Willson ◽  
Stefan Kraus ◽  
Jacques Kluska ◽  
John D. Monnier ◽  
Michel Cure ◽  
...  
Keyword(s):  
Dust Emission ◽  
Three Dimensional ◽  
Position Angle ◽  
Asymmetric Structures ◽  
North East ◽  
The North ◽  
Band Emission ◽  
Upper Limits ◽  
Multi Wavelength ◽  
Differential Imaging

Context. V1247 Orionis harbours a pre-transitional disc with a partially cleared gap. Earlier interferometric and polarimetric observations revealed strong asymmetries both in the gap region and in the outer disc. The presence of a companion was inferred to explain these asymmetric structures and the ongoing disc clearing. Aims. Using an extensive set of multi-wavelength and multi-epoch observations we aimed to identify the origin of the previously detected asymmetries. Methods. We have observed V1247 Ori at three epochs spanning ~678 days using sparse aperture masking interferometry with Keck/NIRC2 and VLT/NACO. In addition, we search for signs of accretion through VLT/SPHERE-ZIMPOL spectral differential imaging in Hα and R-band continuum. Our SMA sub-millimetre interferometry in 880 μm continuum and in the CO(3-2) line allows us to constrain the orientation and direction of rotation of the outer disc. Results. We find the L′-band emission to be dominated by static features which trace forward-scattered dust emission from the inner edge of the outer disc located to the north-east. In H- and K-bands, we see evidence for a companion candidate that moved systematically by 45° within the first ~345 days. The separation of the companion candidate is not well constrained, but the observed position angle change is consistent with Keplerian motion of a body located on a 6 au orbit. From the SMA CO moment map, the location of the disc rim, and the detected orbital motion, we deduced the three-dimensional orientation of the disc. We see no indication of accretion in Hα and set upper limits for an accreting companion. Conclusions. The measured contrast of the companion candidate in H and K is consistent with an actively accreting protoplanet. Hence, we identify V1247 Ori as a unique laboratory for studying companion–disc interactions and disc clearing.

scholarly journals Extragalactic optical and near-infrared foregrounds to 21-cm epoch of reionisation experiments

2017 ◽  
Vol 12 (S333) ◽  
pp. 183-190
Author(s):  
Matt J. Jarvis ◽  
Rebecca A.A. Bowler ◽  
Peter W. Hatfield
Keyword(s):  
Near Infrared ◽  
Neutral Hydrogen ◽  
Limiting Factors ◽  
Additional Information ◽  
Multi Wavelength ◽  
Infrared Surveys ◽  
Cross Correlations ◽  
Extragalactic Surveys ◽  
The Universe ◽  
Lower Redshift

AbstractForeground contamination is one of the most important limiting factors in detecting the neutral hydrogen in the epoch of reionisation. These foregrounds can be roughly split into galactic and extragalactic foregrounds. In these proceedings we highlight information that can be gleaned from multi-wavelength extragalactic surveys in order to overcome this issue. We discuss how clustering information from the lower-redshift, foreground galaxies, can be used as additional information in accounting for the noise associated with the foregrounds. We then go on to highlight the expected contribution of future optical and near-infrared surveys for detecting the galaxies responsible for ionising the Universe. We suggest that these galaxies can also be used to reduce the systematics in the 21-cm epoch of reionisation signal through cross-correlations if enough common area is surveyed.

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