63 research outputs found
H i constraints from the cross-correlation of eBOSS galaxies and Green Bank Telescope intensity maps
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereWe present the joint analysis of Neutral Hydrogen (H I) Intensity Mapping observations with three galaxy samples: the Luminous Red Galaxy (LRG) and Emission Line Galaxy (ELG) samples from the eBOSS survey, and the WiggleZ Dark Energy Survey sample. The H I intensity maps are Green Bank Telescope observations of the redshifted 21cm21cm emission on 100deg2100deg2 covering the redshift range 0.6 < z < 1.0. We process the data by separating and removing the foregrounds present in the radio frequencies with FASTI ICA. We verify the quality of the foreground separation with mock realizations, and construct a transfer function to correct for the effects of foreground removal on the H I signal. We cross-correlate the cleaned H I data with the galaxy samples and study the overall amplitude as well as the scale dependence of the power spectrum. We also qualitatively compare our findings with the predictions by a semianalytical galaxy evolution simulation. The cross-correlations constrain the quantity ΩHIbHIrHI,optΩHIbHIrHI,opt at an effective scale keff, where ΩHIΩHI is the H I density fraction, bHIbHI is the H I bias, and rHI,optrHI,opt the galaxy–hydrogen correlation coefficient, which is dependent on the H I content of the optical galaxy sample. At keff=0.31hMpc−1keff=0.31hMpc−1 we find ΩHIbHIrHI,Wig=[0.58±0.09(stat)±0.05(sys)]×10−3ΩHIbHIrHI,Wig=[0.58±0.09(stat)±0.05(sys)]×10−3 for GBT-WiggleZ, ΩHIbHIrHI,ELG=[0.40±0.09(stat)±0.04(sys)]×10−3ΩHIbHIrHI,ELG=[0.40±0.09(stat)±0.04(sys)]×10−3 for GBT-ELG, and ΩHIbHIrHI,LRG=[0.35±0.08(stat)±0.03(sys)]×10−3ΩHIbHIrHI,LRG=[0.35±0.08(stat)±0.03(sys)]×10−3 for GBT-LRG, at z ≃ 0.8. We also report results at keff=0.24keff=0.24 and keff=0.48hMpc−1keff=0.48hMpc−1. With little information on H I parameters beyond our local Universe, these are amongst the most precise constraints on neutral hydrogen density fluctuations in an underexplored redshift rang
The varying w spread spectrum effect for radio interferometric imaging
We study the impact of the spread spectrum effect in radio interferometry on
the quality of image reconstruction. This spread spectrum effect will be
induced by the wide field-of-view of forthcoming radio interferometric
telescopes. The resulting chirp modulation improves the quality of
reconstructed interferometric images by increasing the incoherence of the
measurement and sparsity dictionaries. We extend previous studies of this
effect to consider the more realistic setting where the chirp modulation varies
for each visibility measurement made by the telescope. In these first
preliminary results, we show that for this setting the quality of
reconstruction improves significantly over the case without chirp modulation
and achieves almost the reconstruction quality of the case of maximal, constant
chirp modulation.Comment: 1 page, 1 figure, Proceedings of the Biomedical and Astronomical
Signal Processing Frontiers (BASP) workshop 201
The fore ground transfer function for H I intensity mapping signal reconstruction: MeerKLASS and precision cosmology applications
Blind cleaning methods are currently the preferred strategy for handling foreground contamination in single-dish H I intensity mapping surv e ys. Despite the increasing sophistication of blind techniques, some signal loss will be inevitable across all scales. Constructing a corrective transfer function using mock signal injection into the contaminated data has been a practice relied on for H I intensity mapping experiments. Ho we ver, assessing whether this approach is viable for future intensity mapping surv e ys, where precision cosmology is the aim, remains unexplored. In this work, using simulations, we validate for the first time the use of a foreground transfer function to reconstruct power spectra of foreground-cleaned low-redshift intensity maps and look to e xpose an y limitations. We rev eal that ev en when aggressiv e fore ground cleaning is required, which causes > 50 per cent ne gativ e bias on the largest scales, the power spectrum can be reconstructed using a transfer function to within sub-per cent accuracy. We specifically outline the recipe for constructing an unbiased transfer function, highlighting the pitfalls if one deviates from this recipe, and also correctly identify how a transfer function should be applied in an autocorrelation power spectrum. We validate a method that utilizes the transfer function variance for error estimation in foreground-cleaned power spectra. Finally, we demonstrate how incorrect fiducial parameter assumptions (up to ±100 per cent bias) in the generation of mocks, used in the construction of the transfer function, do not significantly bias signal reconstruction or parameter inference (inducing < 5 per cent bias in reco v ered values)
Foreground Subtraction in Intensity Mapping with the SKA
21cm intensity mapping experiments aim to observe the diffuse neutral
hydrogen (HI) distribution on large scales which traces the Cosmic structure.
The Square Kilometre Array (SKA) will have the capacity to measure the 21cm
signal over a large fraction of the sky. However, the redshifted 21cm signal in
the respective frequencies is faint compared to the Galactic foregrounds
produced by synchrotron and free-free electron emission. In this article, we
review selected foreground subtraction methods suggested to effectively
separate the 21cm signal from the foregrounds with intensity mapping
simulations or data. We simulate an intensity mapping experiment feasible with
SKA phase 1 including extragalactic and Galactic foregrounds. We give an
example of the residuals of the foreground subtraction with a independent
component analysis and show that the angular power spectrum is recovered within
the statistical errors on most scales. Additionally, the scale of the Baryon
Acoustic Oscillations is shown to be unaffected by foreground subtraction.Comment: This article is part of the 'SKA Cosmology Chapter, Advancing
Astrophysics with the SKA (AASKA14), Conference, Giardini Naxos (Italy), June
9th-13th 2014
Detecting the H I power spectrum in the post-reionization Universe with SKA-Low
We present a survey strategy to detect the neutral hydrogen (H i) power spectrum at 5 &lt; z &lt; 6 using the SKA-Low radio telescope in presence of foregrounds and instrumental effects. We simulate observations of the inherently weak HI signal post-reionization with varying levels of noise and contamination with foreground amplitudes equivalent to residuals after sky model subtraction. We find that blind signal separation methods on imaged data are required in order to recover the H i signal at large cosmological scales. Comparing different methods of foreground cleaning, we find that Gaussian Process Regression (GPR) performs better than Principle Component Analysis (PCA), with the key difference being that GPR uses smooth kernels for the total data covariance. The integration time of one field needs to be larger than ∼250 hours to provide large enough signal-to-noise ratio to accurately model the data covariance for foreground cleaning. Images within the primary beam field-of-view give measurements of the H i power spectrum at scales k ∼ 0.02 Mpc−1 − 0.3 Mpc−1 with signal-to-noise ratio ∼2 − 5 in Δ[log(k/Mpc−1)] = 0.25 bins assuming an integration time of 600 hours. Systematic effects, which introduce small-scale fluctuations across frequency channels, need to be ≲ 5 × 10−5 to enable unbiased measurements outside the foreground wedge. Our results provide an important validation towards using the SKA-Low array for measuring the H i power spectrum in the post-reionization Universe
The foreground transfer function for HI intensity mapping signal reconstruction: MeerKLASS and precision cosmology applications
Blind cleaning methods are currently the preferred strategy for handling
foreground contamination in single-dish HI intensity mapping surveys. Despite
the increasing sophistication of blind techniques, some signal loss will be
inevitable across all scales. Constructing a corrective transfer function using
mock signal injection into the contaminated data has been a practice relied on
for HI intensity mapping experiments. However, assessing whether this approach
is viable for future intensity mapping surveys where precision cosmology is the
aim, remains unexplored. In this work, using simulations, we validate for the
first time the use of a foreground transfer function to reconstruct power
spectra of foreground-cleaned low-redshift intensity maps and look to expose
any limitations. We reveal that even when aggressive foreground cleaning is
required, which causes negative bias on the largest scales, the
power spectrum can be reconstructed using a transfer function to within
sub-percent accuracy. We specifically outline the recipe for constructing an
unbiased transfer function, highlighting the pitfalls if one deviates from this
recipe, and also correctly identify how a transfer function should be applied
in an auto-correlation power spectrum. We validate a method that utilises the
transfer function variance for error estimation in foreground-cleaned power
spectra. Finally, we demonstrate how incorrect fiducial parameter assumptions
(up to bias) in the generation of mocks, used in the construction
of the transfer function, do not significantly bias signal reconstruction or
parameter inference (inducing bias in recovered values).Comment: 25 pages, 20 figures. See Figure 4 for the main demonstration of the
transfer function's performance for reconstructing signal loss from
foreground cleaning. Submitted to MNRAS for publicatio
Cosmology with a SKA HI intensity mapping survey
Advancing Astrophysics with the Square Kilometre Array
June 8-13, 2014
Giardini Naxos, ItalyHI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of
the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI
as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of
the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve
individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity
maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the
baryon acoustic oscillation and redshift space distortion features in the matter power spectrum –
thus determining the expansion and growth history of the Universe – these surveys can provide
powerful tests of dark energy models and modifications to General Relativity. They can also be
used to probe physics on extremely large scales, where precise measurements of spatial curvature
and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring
the sum of neutrino masses; and at high redshifts where non-standard evolution models can be
probed. We discuss the impact of foregrounds as well as various instrumental and survey design
parameters on the achievable constraints. In particular we analyse the feasibility of using the
SKA1 autocorrelations to probe the large-scale signal.Web of Scienc
SKAO HI intensity mapping: blind foreground subtraction challenge
Neutral Hydrogen Intensity Mapping (H I IM) surveys will be a powerful new probe of cosmology. However, strong astrophysical
foregrounds contaminate the signal and their coupling with instrumental systematics further increases the data cleaning
complexity. In this work, we simulate a realistic single-dish HI IM survey of a 5000 deg2 patch in the 950–1400 MHz
range, with both the MID telescope of the SKA Observatory (SKAO) and MeerKAT, its precursor. We include a state-of-the-art
HI simulation and explore different foreground models and instrumental effects such as non-homogeneous thermal noise and
beam side lobes. We perform the first Blind Foreground Subtraction Challenge for HI IM on these synthetic data cubes, aiming
to characterize the performance of available foreground cleaning methods with no prior knowledge of the sky components and
noise level. Nine foreground cleaning pipelines joined the challenge, based on statistical source separation algorithms, blind
polynomial fitting, and an astrophysical-informed parametric fit to foregrounds. We devise metrics to compare the pipeline
performances quantitatively. In general, they can recover the input maps’ two-point statistics within 20 per cent in the range of
scales least affected by the telescope beam. However, spurious artefacts appear in the cleaned maps due to interactions between
the foreground structure and the beam side lobes. We conclude that it is fundamental to develop accurate beam deconvolution
algorithms and test data post-processing steps carefully before cleaning. This study was performed as part of SKAO preparatory
work by the HI IM Focus Group of the SKA Cosmology Science Working Group
MeerKLASS: MeerKAT Large Area Synoptic Survey
We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over for hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science,
"MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201
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