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.

scholarly journals Impact of foregrounds on H i intensity mapping cross-correlations with optical surveys

2019 ◽  
Vol 488 (4) ◽  
pp. 5452-5472 ◽  
Author(s):  
Steven Cunnington ◽  
Laura Wolz ◽  
Alkistis Pourtsidou ◽  
David Bacon
Keyword(s):  
Neutral Hydrogen ◽  
Optical Data ◽  
Line Of Sight ◽  
Redshift Distribution ◽  
Intensity Mapping ◽  
Fast Independent Component Analysis ◽  
Cross Correlations ◽  
The Cross ◽  
The Impact ◽  
Optical Surveys

ABSTRACT The future of precision cosmology could benefit from cross-correlations between intensity maps of unresolved neutral hydrogen (H i) and more conventional optical galaxy surveys. A major challenge that needs to be overcome is removing the 21cm foreground emission that contaminates the cosmological H i signal. Using N-body simulations, we simulate H i intensity maps and optical catalogues that share the same underlying cosmology. Adding simulated foreground contamination and using state-of-the-art reconstruction techniques, we investigate the impacts that 21cm foregrounds and other systematics have on these cross-correlations. We find that the impact a Fast Independent Component Analysis 21cm foreground clean has on the cross-correlations with spectroscopic optical surveys with well-constrained redshifts is minimal. However, problems arise when photometric surveys are considered: We find that a redshift uncertainty σz ≥ 0.04 causes significant degradation in the cross-power spectrum signal. We diagnose the main root of these problems, which relates to arbitrary amplitude changes along the line of sight in the intensity maps caused by the foreground clean and suggest solutions that should be applicable to real data. These solutions involve a reconstruction of the line-of-sight temperature means using the available overlapping optical data along with an artificial extension to the H i data through redshift to address edge effects. We then put these solutions through a further test in a mock experiment that uses a clustering-based redshift estimation technique to constrain the photometric redshifts of the optical sample. We find that with our suggested reconstruction, cross-correlations can be utilized to make an accurate prediction of the optical redshift distribution.

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.

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

scholarly journals Assessing Changes in Soil Erosion Rates: A Markov Chain Analysis

1999 ◽  
Vol 31 (3) ◽  
pp. 611-622 ◽  
Author(s):  
Rhonda Skaggs ◽  
Soumen Ghosh
Keyword(s):  
Markov Chain ◽  
Soil Erosion ◽  
Great Plains ◽  
Markov Chain Analysis ◽  
Conservation Policies ◽  
Erosion Rates ◽  
National Resources Inventory ◽  
Long Run ◽  
Chain Analysis ◽  
Soil Erosion Rates

AbstractMarkov chain analysis (one-step and long-run) is applied to the National Resources Inventory (NRI) database to evaluate changes in wind-based soil erosion rates over time. The research compares changes in soil erosion rates between NRI sample sites with and without applied conservation practices for a random sample of Great Plains counties. No significant differences between sites are found for half of the counties evaluated. The effectiveness and efficiency of conservation policies are thus questioned in light of these research results.

Markov chain analysis of Leading Ones problem

2017 ◽  
Vol 22 (4) ◽  
pp. 443-448 ◽  
Author(s):  
Yifei Du ◽  
Kenji Aoki ◽  
Makoto Sakamoto ◽  
Hiroshi Furutani ◽  
Kunihito Yamamori
Keyword(s):  
Markov Chain ◽  
Markov Chain Analysis ◽  
Chain Analysis

262 Markov Chain Analysis of Time Dependent Changes in AMR Using the 2011 ISHLT pAMR Classification

2012 ◽  
Vol 31 (4) ◽  
pp. S95
Author(s):  
G. Snow ◽  
J. Stehlik ◽  
E.H. Hammond ◽  
K. Brunisholz ◽  
E. Gilbert ◽  
...  
Keyword(s):  
Markov Chain ◽  
Time Dependent ◽  
Markov Chain Analysis ◽  
Chain Analysis

scholarly journals Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization

2011 ◽  
Vol 28 (1) ◽  
pp. 46-57 ◽  
Author(s):  
B. Pindor ◽  
J. S. B. Wyithe ◽  
D. A. Mitchell ◽  
S. M. Ord ◽  
R. B. Wayth ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Dynamic Range ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
Point Sources ◽  
Field Of View ◽  
Bright Point ◽  
Line Of Sight ◽  
Diffuse Background

AbstractBright point sources associated with extragalactic active galactic nuclei and radio galaxies are an important foreground for low-frequency radio experiments aimed at detecting the redshifted 21-cm emission from neutral hydrogen during the epoch of reionization. The frequency dependence of the synthesized beam implies that the sidelobes of these sources will move across the field of view as a function of observing frequency, hence frustrating line-of-sight foreground subtraction techniques. We describe a method for subtracting these point sources from dirty maps produced by an instrument such as the MWA. This technique combines matched filters with an iterative centroiding scheme to locate and characterize point sources in the presence of a diffuse background. Simulations show that this technique can improve the dynamic range of epoch-of-reionization maps by 2—3 orders of magnitude.

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