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 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 Implications of the z > 5 Lyman-α forest for the 21-cm power spectrum from the epoch of reionization

2021 ◽  
Author(s):  
Janakee Raste ◽  
Girish Kulkarni ◽  
Laura C Keating ◽  
Martin G Haehnelt ◽  
Jonathan Chardin ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Power Spectrum ◽  
Intergalactic Medium ◽  
Neutral Hydrogen ◽  
Redshift Range ◽  
Sky Temperature ◽  
Conventional Models

Abstract Our understanding of the intergalactic medium at redshifts z = 5–6 has improved considerably in the last few years due to the discovery of quasars with z > 6 that enable Lyman-α forest studies at these redshifts. A realisation from this has been that hydrogen reionization could end much later than previously thought, so that large “islands” of cold, neutral hydrogen could exist in the IGM at redshifts z = 5–6. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as hera, ska, lofar, and mwa. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as $\Delta ^2_{21}=10~\mathrm{mK}^2$ at k ∼ 0.1 h cMpc−1 at z = 5–6. This value of the power spectrum is several orders of magnitude higher than that in conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by hera and ska1-low in ∼1000 hours, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data.

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 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.

scholarly journals Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution  Ly α forest spectra

2020 ◽  
Vol 494 (4) ◽  
pp. 5091-5109 ◽  
Author(s):  
Prakash Gaikwad ◽  
Michael Rauch ◽  
Martin G Haehnelt ◽  
Ewald Puchwein ◽  
James S Bolton ◽  
...  
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Intergalactic Medium ◽  
Thermal State ◽  
Neutral Hydrogen ◽  
High Spectral Resolution ◽  
Profile Fitting ◽  
Density Relation ◽  
Width Distribution ◽  
Hydrodynamical Simulations

ABSTRACT We compare a sample of five high-resolution, high S/N  Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F, similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8  km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.

scholarly journals Probing the high-z IGM with the hyperfine transition of 3He+

2020 ◽  
Vol 497 (1) ◽  
pp. 572-580 ◽  
Author(s):  
Shivan Khullar ◽  
Qingbo Ma ◽  
Philipp Busch ◽  
Benedetta Ciardi ◽  
Marius B Eide ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Signal To Noise Ratio ◽  
Neutral Hydrogen ◽  
Noise Power ◽  
Large Collection ◽  
X Ray ◽  
Hyperfine Transition ◽  
The One ◽  
X Ray Binaries ◽  
Insight Into

ABSTRACT The hyperfine transition of 3He+ at 3.5 cm has been thought as a probe of the high-z IGM, since it offers a unique insight into the evolution of the helium component of the gas, as well as potentially give an independent constraint on the 21 cm signal from neutral hydrogen. In this paper, we use radiative transfer simulations of reionization driven by sources such as stars, X-ray binaries, accreting black holes and shock heated interstellar medium, and simulations of a high-z quasar to characterize the signal and analyse its prospects of detection. We find that the peak of the signal lies in the range ∼1–50 μK for both environments, but while around the quasar it is always in emission, in the case of cosmic reionization a brief period of absorption is expected. As the evolution of He ii is determined by stars, we find that it is not possible to distinguish reionization histories driven by more energetic sources. On the other hand, while a bright QSO produces a signal in 21 cm that is very similar to the one from a large collection of galaxies, its signature in 3.5 cm is very peculiar and could be a powerful probe to identify the presence of the QSO. We analyse the prospects of the signal’s detectability using SKA1-mid as our reference telescope. We find that the noise power spectrum dominates over the power spectrum of the signal, although a modest signal-to-noise ratio can be obtained when the wavenumber bin width and the survey volume are sufficiently large.

scholarly journals HD 189733 b: bow shock or no shock?

2018 ◽  
Vol 619 ◽  
pp. A96 ◽  
Author(s):  
S. Kohl ◽  
M. Salz ◽  
S. Czesla ◽  
J. H. M. M. Schmitt
Keyword(s):  
Time Series ◽  
Neutral Hydrogen ◽  
Periodic Variation ◽  
Bow Shock ◽  
Time Variability ◽  
Stellar Activity ◽  
Hot Jupiters ◽  
Upper Limits ◽  
In Transit ◽  
Infrared Triplet

Context. Hot Jupiters are surrounded by extended atmospheres of neutral hydrogen. Observations have provided evidence for in-transit hydrogen Hα absorption as well as variable pre-transit absorption signals. These have been interpreted in terms of a bow shock or an accretion stream that transits the host star before the planet. Aims. We test the hypothesis of planetary-related Hα absorption by studying the time variability of the Hα and stellar activity-sensitive calcium lines in high-resolution TIGRE (Telescopio Internacional de Guanajuato Robótico Espectroscópico) spectra of the planet host HD 189733. Methods. In the framework of an observing campaign spanning several months, the host star was observed several times per week randomly sampling the orbital phases of the planet. We determine the equivalent width in the Hα and Ca IRT(calcium infrared triplet) lines, and subtract stellar rotationally induced activity from the Hα time series via its correlation with the IRT evolution. The residuals are explored for significant differences between the pre-, in-, and out-of-transit phases. Results. We find strong stellar rotational variation with a lifetime of about 20–30 days in all activity indicators, but the corrected Hα time series exhibits no significant periodic variation. We exclude the presence of more than 6.2 mÅ pre-transit absorption and 5.6 mÅ in-transit absorption in the corrected Hα data at a 99% confidence level. Conclusions. Previously observed Hα absorption signals exceed our upper limits, but they could be related to excited atmospheric states. The Hα variability in the HD 189733 system is dominated by stellar activity, and observed signals around the planetary transit may well be caused by short-term stellar variability.

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