scholarly journals Comparing foreground removal techniques for recovery of the LOFAR-EoR 21 cm power spectrum

2020 ◽  
Vol 500 (2) ◽  
pp. 2264-2277 ◽  
Author(s):  
Ian Hothi ◽  
Emma Chapman ◽  
Jonathan R Pritchard ◽  
F G Mertens ◽  
L V E Koopmans ◽  
...  
Keyword(s):  
Neutral Hydrogen ◽  
Instrumental Effects ◽  
Independent Components ◽  
Upper Limit ◽  
Current Usage ◽  
Noise Limit ◽  
Instrumental Effect ◽  
Removal Technique ◽  
Foreground Removal ◽  
Mode Mixing

ABSTRACT We compare various foreground removal techniques that are being utilized to remove bright foregrounds in various experiments aiming to detect the redshifted 21 cm signal of neutral hydrogen from the epoch of reionization. In this work, we test the performance of removal techniques (FastICA, GMCA, and GPR) on 10 nights of LOFAR data and investigate the possibility of recovering the latest upper limit on the 21 cm signal. Interestingly, we find that GMCA and FastICA reproduce the most recent 2σ upper limit of $\Delta ^2_{21} \lt $ (73)2 mK2 at k = 0.075 hcMpc−1, which resulted from the application of GPR. We also find that FastICA and GMCA begin to deviate from the noise-limit at k-scales larger than ∼0.1 hcMpc−1. We then replicate the data via simulations to see the source of FastICA and GMCA’s limitations, by testing them against various instrumental effects. We find that no single instrumental effect, such as primary beam effects or mode-mixing, can explain the poorer recovery by FastICA and GMCA at larger k-scales. We then test scale-independence of FastICA and GMCA, and find that lower k-scales can be modelled by a smaller number of independent components. For larger scales (k ≳ 0.1 hcMpc−1), more independent components are needed to fit the foregrounds. We conclude that, the current usage of GPR by the LOFAR collaboration is the appropriate removal technique. It is both robust and less prone to overfitting, with future improvements to GPR’s fitting optimization to yield deeper limits.

scholarly journals The degeneracy between primordial non-Gaussianity and foregrounds in 21 cm intensity mapping experiments

2020 ◽  
Vol 499 (3) ◽  
pp. 4054-4067
Author(s):  
Steven Cunnington ◽  
Stefano Camera ◽  
Alkistis Pourtsidou
Keyword(s):  
Nuisance Parameter ◽  
Neutral Hydrogen ◽  
Real Data ◽  
Line Of Sight ◽  
Markov Chain Analysis ◽  
Significant Progress ◽  
Intensity Mapping ◽  
Chain Analysis ◽  
Parallel Text ◽  
Foreground Removal

ABSTRACT Potential evidence for primordial non-Gaussianity (PNG) is expected to lie in the largest scales mapped by cosmological surveys. Forthcoming 21 cm intensity mapping experiments will aim to probe these scales by surveying neutral hydrogen (H i) within galaxies. However, foreground signals dominate the 21 cm emission, meaning foreground cleaning is required to recover the cosmological signal. The effect this has is to damp the H i power spectrum on the largest scales, especially along the line of sight. Whilst there is agreement that this contamination is potentially problematic for probing PNG, it is yet to be fully explored and quantified. In this work, we carry out the first forecasts on fNL that incorporate simulated foreground maps that are removed using techniques employed in real data. Using an Monte Carlo Markov Chain analysis on an SKA1-MID-like survey, we demonstrate that foreground cleaned data recovers biased values [$f_{\rm NL}= -102.1_{-7.96}^{+8.39}$ (68 per cent CL)] on our fNL = 0 fiducial input. Introducing a model with fixed parameters for the foreground contamination allows us to recover unbiased results ($f_{\rm NL}= -2.94_{-11.9}^{+11.4}$). However, it is not clear that we will have sufficient understanding of foreground contamination to allow for such rigid models. Treating the main parameter $k_\parallel ^\text{FG}$ in our foreground model as a nuisance parameter and marginalizing over it, still recovers unbiased results but at the expense of larger errors ($f_{\rm NL}= 0.75^{+40.2}_{-44.5}$), which can only be reduced by imposing the Planck 2018 prior. Our results show that significant progress on understanding and controlling foreground removal effects is necessary for studying PNG with H i intensity mapping.

Optimization of Detectability in Laser-Based Polarimeters

1989 ◽  
Vol 43 (8) ◽  
pp. 1337-1341 ◽  
Author(s):  
Xiaobing Xi ◽  
Edward S. Yeung
Keyword(s):  
Shot Noise ◽  
Experimental Verification ◽  
High Frequency ◽  
Ohmic Heating ◽  
Unit Length ◽  
Power Input ◽  
Upper Limit ◽  
High Modulation ◽  
Noise Limit ◽  
Shot Noise Limit

To optimize the performance of a laser-based polarimeter, a mathematical simulation was performed. High-modulation currents allow a corresponding increase in signal. However, the effect of ohmic heating puts an upper limit on the power input to the solenoid. With this constraint, one can systematically choose the wire diameter and the number of turns per unit length. An experimental verification of the optimized parameters provided performance approaching the shot-noise limit. By using higher modulation currents, one can operate at 1 kHz to achieve detectability in the microdegree range, without the complications of high-frequency (100 kHz) modulation.

scholarly journals Comparative rainfall data analysis from two vertically pointing radars, an optical disdrometer, and a rain gauge

2008 ◽  
Vol 15 (6) ◽  
pp. 987-997 ◽  
Author(s):  
E. I. Nikolopoulos ◽  
A. Kruger ◽  
W. F. Krajewski ◽  
C. R. Williams ◽  
K. S. Gage
Keyword(s):  
Comparative Analysis ◽  
Temporal Variability ◽  
Rain Gauge ◽  
Iowa City ◽  
Rainfall Data ◽  
Instrumental Effects ◽  
Remote Sensors ◽  
X Band ◽  
Derived Properties ◽  
Instrumental Effect

Abstract. The authors present results of a comparative analysis of rainfall data from several ground-based instruments. The instruments include two vertically pointing Doppler radars, S-band and X-band, an optical disdrometer, and a tipping-bucket rain gauge. All instruments were collocated at the Iowa City Municipal Airport in Iowa City, Iowa, for a period of several months. The authors used the rainfall data derived from the four instruments to first study the temporal variability and scaling characteristics of rainfall and subsequently assess the instrumental effects on these derived properties. The results revealed obvious correspondence between the ground and remote sensors, which indicates the significance of the instrumental effect on the derived properties.

scholarly journals Sensitive Search for HI in E and SO galaxies

1983 ◽  
Vol 100 ◽  
pp. 305-306
Author(s):  
Norbert Thonnard
Keyword(s):  
Neutral Hydrogen ◽  
Optical Image ◽  
Type I ◽  
Hydrogen Line ◽  
Upper Limit

Do elliptical and SO galaxies in which type I supernovae (SNI) were detected contain more gas than those without SNI detections? Thirteen E and SO galaxies in the Virgo and Pegasus I clusters, seven with SNI detections and six without, were mapped well beyond the optical image at the 21-cm neutral hydrogen line. No HI was detected. In Virgo, the upper limit to MMI/LB is between 0.0005 and 0.0024.

scholarly journals Measuring the distance to the black hole candidate X-ray binary MAXI J1348–630 using H i absorption

2020 ◽  
Vol 501 (1) ◽  
pp. L60-L64
Author(s):  
J Chauhan ◽  
J C A Miller-Jones ◽  
W Raja ◽  
J R Allison ◽  
P F L Jacob ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutral Hydrogen ◽  
Tangent Point ◽  
X Ray ◽  
Black Hole Candidate ◽  
Upper Limit ◽  
Local Standard ◽  
Point Distance ◽  
Spectral State ◽  
Local Standard Of Rest

ABSTRACT We present neutral hydrogen (H i) absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348–630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP H i spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of −31 ± 4 km s−1 for MAXI J1348–630, as compared to −50 ± 4 km s−1 for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of $2.2^{+0.5}_{-0.6}$ kpc for MAXI J1348–630, and a strong upper limit of the tangent point distance at 5.3 ± 0.1 kpc. Our preferred distance implies that MAXI J1348–630 reached 17 ± 10  per cent of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at 2.5 ± 1.5  per cent of the Eddington luminosity. The MeerKAT H i spectrum of MAXI J1348–630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.

scholarly journals SILVERRUSH. XI. Constraints on the Lyα Luminosity Function and Cosmic Reionization at z = 7.3 with Subaru/Hyper Suprime-Cam

2021 ◽  
Vol 923 (2) ◽  
pp. 229
Author(s):  
Hinako Goto ◽  
Kazuhiro Shimasaku ◽  
Satoshi Yamanaka ◽  
Rieko Momose ◽  
Makoto Ando ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Intergalactic Medium ◽  
Neutral Hydrogen ◽  
Neutral Fraction ◽  
Estimation Methods ◽  
Large Area ◽  
Upper Limit ◽  
Narrowband Imaging ◽  
First Time

Abstract The Lyα luminosity function (LF) of Lyα emitters (LAEs) has been used to constrain the neutral hydrogen fraction in the intergalactic medium (IGM) and thus the timeline of cosmic reionization. Here we present the results of a new narrowband imaging survey for z = 7.3 LAEs in a large area of ∼3 deg2 with Subaru/Hyper Suprime-Cam. No LAEs are detected down to L Lyα ≃ 1043.2 erg s−1 in an effective cosmic volume of ∼2 × 106 Mpc3, placing an upper limit on the bright part of the z = 7.3 Lyα LF for the first time and confirming a decrease in bright LAEs from z = 7.0. By comparing this upper limit with the Lyα LF in the case of fully ionized IGM, which is predicted using an observed z = 5.7 Lyα LF on the assumption that the intrinsic Lyα LF evolves in the same way as the UV LF, we obtain the relative IGM transmission T Ly α IGM ( 7.3 ) / T Ly α IGM ( 5.7 ) < 0.77 and then the volume-averaged neutral fraction x H I(7.3) > 0.28. Cosmic reionization is thus still ongoing at z = 7.3, consistent with results from other x H I estimation methods. A similar analysis using literature Lyα LFs finds that at z = 6.6 and 7.0, the observed Lyα LF agrees with the predicted one, consistent with full ionization.

scholarly journals Multipole expansion for H i intensity mapping experiments: simulations and modelling

2020 ◽  
Vol 496 (1) ◽  
pp. 415-433 ◽  
Author(s):  
Steven Cunnington ◽  
Alkistis Pourtsidou ◽  
Paula S Soares ◽  
Chris Blake ◽  
David Bacon
Keyword(s):  
Monte Carlo ◽  
Markov Chain ◽  
Multipole Expansion ◽  
Instrumental Effects ◽  
Fourier Space ◽  
Reasonable Accuracy ◽  
Intensity Mapping ◽  
Expansion Technique ◽  
The Impact ◽  
Foreground Removal

ABSTRACT We present a framework and an open-source python toolkit to analyse the two-point statistics of 3D fluctuations in the context of H i intensity maps using the multipole expansion formalism. We include simulations of the cosmological H i signal using N-body and lognormal methods, foregrounds and their removal, as well as instrumental effects. Using these simulations and analytical modelling, we investigate the impact of foreground cleaning and the instrumental beam on the power spectrum multipoles as well as on the Fourier space clustering wedges. We find that both the instrumental beam and the foreground removal can produce a quadrupole (and a hexadecapole) signal, and demonstrate the importance of controlling and accurately modelling these effects for precision radio cosmology. We conclude that these effects can be modelled with reasonable accuracy using our multipole expansion technique. We also perform a Markov Chain Monte Carlo (MCMC) analysis to showcase the effect of foreground cleaning on the estimation of the H i abundance and bias parameters. The accompanying python toolkit is available at https://github.com/IntensityTools/MultipoleExpansion, and includes an interactive suite of examples to aid new users.

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 HIR4: cosmology from a simulated neutral hydrogen full sky using Horizon Run 4

2020 ◽  
Vol 495 (2) ◽  
pp. 1788-1806
Author(s):  
Jacobo Asorey ◽  
David Parkinson ◽  
Feng Shi ◽  
Yong-Seon Song ◽  
Kyungjin Ahn ◽  
...  
Keyword(s):  
Large Scale ◽  
Cosmological Parameters ◽  
Line Emission ◽  
Neutral Hydrogen ◽  
Angular Power Spectrum ◽  
Intensity Mapping ◽  
Free Case ◽  
Foreground Removal ◽  
The Universe ◽  
Mapping Information

ABSTRACT The distribution of cosmological neutral hydrogen will provide a new window into the large-scale structure of the Universe with the next generation of radio telescopes and surveys. The observation of this material, through 21 cm line emission, will be confused by foreground emission in the same frequencies. Even after these foregrounds are removed, the reconstructed map may not exactly match the original cosmological signal, which will introduce systematic errors and offset into the measured correlations. In this paper, we simulate future surveys of neutral hydrogen using the Horizon Run 4 (HR4) cosmological N-body simulation. We generate H i intensity maps from the HR4 halo catalogue, and combine with foreground radio emission maps from the Global Sky Model, to create accurate simulations over the entire sky. We simulate the H i sky for the frequency range 700–800 MHz, matching the sensitivity of the Tianlai pathfinder. We test the accuracy of the fastICA, PCA, and log-polynomial fitting foreground removal methods to recover the input cosmological angular power spectrum and measure the parameters. We show the effect of survey noise levels and beam sizes on the recovered the cosmological constraints. We find that while the reconstruction removes power from the cosmological 21 cm distribution on large scales, we can correct for this and recover the input parameters in the noise-free case. However, the effect of noise and beam size of the Tianlai pathfinder prevents accurate recovery of the cosmological parameters when using only intensity mapping information.

A new upper limit on the density of generally distributed intergalactic neutral hydrogen

1987 ◽  
Vol 318 ◽  
pp. L11 ◽  
Author(s):  
Charles C. Steidel ◽  
Wallace L. W. Sargent
Keyword(s):  
Neutral Hydrogen ◽  
Upper Limit
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