On the contamination of the global 21 cm signal from polarized foregrounds

Spinelli, M.; Bernardi, G.; Santos, Mário G.

doi:10.1093/mnras/stz2425

Cited by 42 publications

(27 citation statements)

References 64 publications

(126 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Bowman et al (2018) has a tentative detection of this global signal, with the absorption depth and width, currently, unexplained. Though there have been claims that the results could be explained by exotic physics (Fialkov et al 2018), potential unaccounted for systematics (Singh & Subrahmanyan 2019), foreground polarizations (Spinelli et al 2019), or modelling (Hills et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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

Hothi

Chapman

Pritchard

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

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

Hothi

Chapman

Pritchard

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…264 Polarized foreground emission may have contaminated the observations. 265 However, independent analyses of the data are unable to refute the principal claims. 266 There is consensus that the EDGES results need confirmation.…”

Section: Cosmic Dawn the Epoch Of Reionization And Low-frequency Ramentioning

confidence: 99%

Enabling discoveries: a review of 30 years of advanced technologies and instrumentation at the National Science Foundation

Kurczynski

Milojević

2020

J. Astron. Telesc. Instrum. Syst.

View full text Add to dashboard Cite

Over its more than 30-year history, the Advanced Technologies and Instrumentation (ATI) program has provided grants to support technology development and instrumentation for ground-based astronomy. Through a combination of automated literature assessment and indepth literature review, we present a survey of ATI-funded research and its impact on astronomy and society. Award acknowledgment and literature citation statistics for ATI are comparable to a comparison astronomy grant program that does not support technology development. Citation statistics for both NSF-funded programs exceed those of the general astronomical literature. Numerous examples demonstrate the significant, long-term impact of ATI-supported research in astronomy. As part of this impact, ATI grants have provided many early career researchers the opportunity to gain critical professional experience. However, technology development unfolds over a time period that is longer than an individual grant. A longitudinal perspective shows that investments in technology and instrumentation have led to extraordinary scientific progress. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

show abstract

“…We considered possible alternative explanations for the observed feature, such as an instrumental artifact caused by receiver calibration errors or unmodeled frequencydependence of the antenna beam converting angular foreground power into spectral features. Others have also proposed alternative instrumental or analysis explanations (Bradley et al 2019;Sims & Pober 2020;Hills et al 2018) or polarized foregrounds (Spinelli et al 2019). We conducted a number of validation tests that disfavoured instrumentation effects, including repeating the measurement with multiple instruments, with the antenna at different rotation angles, and using multiple calibration solutions.…”

Section: Introductionmentioning

confidence: 99%

Validation of EDGES Low-Band Antenna Beam Model

Mahesh,

Bowman,

Mozdzen

et al. 2021

Preprint

View full text Add to dashboard Cite

The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the electromagnetic beam model of the low-band (50-100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes of numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated driftscan observation from an early EDGES low-band instrument that had a 10 m × 10 m ground plane, we find residual levels after fitting and removing a five-term foreground model to data binned in Local Sidereal Time (LST) average about 250 mK with ±40 mK variation between numerical solvers. A similar analysis of the primary 30 m × 30 m sawtooth ground plane reduced the LST-averaged residuals to about 90 mK with ±10 mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power which is within 4% of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that soil conductivity of 0.02 Sm −1 and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by Sutinjo et al. (2015) for the Murchison Radio-astronomy Observatory, where EDGES is located.

show abstract

On the contamination of the global 21 cm signal from polarized foregrounds

Cited by 42 publications

References 64 publications

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

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

Enabling discoveries: a review of 30 years of advanced technologies and instrumentation at the National Science Foundation

Validation of EDGES Low-Band Antenna Beam Model

Contact Info

Product

Resources

About