Foreground removal using<scp>fastica</scp>: a showcase of LOFAR-EoR

Chapman, Emma; Abdalla, F. B.; Harker, G.; Jelić, Vibor; Labropoulos, P.; Zaroubi, Saleem; Brentjens, M. A.; Bruyn, de Antonius; Koopmans, L. V. E.

doi:10.1111/j.1365-2966.2012.21065.x

Cited by 189 publications

(188 citation statements)

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“…Thus, the EoR signal can be extracted by fitting out the smooth component of the foregrounds along the frequency direction. This can be achieved by using polynomials (e.g., Santos et al 2005;Wang et al 2006;McQuinn et al 2006;Bowman et al 2006;Jelić et al 2008, and references therein), or more advanced non-parametric methods (Harker et al 2009a;Chapman et al 2012Chapman et al , 2013). However, one should be careful in using polynomials.…”

Section: Removalmentioning

confidence: 99%

“…If the order of the polynomial is set too large, the EoR signal could be fitted out. Hence, in principle it is better to fit the foregrounds non-parametrically -allowing the data to determine their shape -rather than selecting some functional form in advance and then fitting its parameters (Harker et al 2009a;Chapman et al 2012). In addition, fitting directly to the visibilities rather than the image cubes might be another avenue to remove foregrounds.…”

Section: Removalmentioning

confidence: 99%

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Reionization and the Cosmic Dawn with the Square Kilometre Array

et al. 2013

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The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe. This 21cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an Executive SummaryThe Square Kilometre Array (SKA) will have a low frequency component (AA-low/SKA-low 1 ) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe (see SKA Memo 125). It is during this phase that the first building blocks of the galaxies that we see around us today, including our own Milky Way, were formed. It is a crucial period for understanding the history of the Universe and one for which we have currently very little observational data.We divide the period into two different phases based on the physical processes which affect the Intergalactic Medium. The first period, which we call the Cosmic Dawn, saw the formation of the first stars and accreting black holes, which changed the quantum state of the still neutral Intergalactic Medium. The second period, known as the Epoch of Reionization, is the one during which large areas between the galaxies were photo-ionized by the radiation produced in galaxies and which ended when the Intergalactic Medium had become completely ionized.Observations of the redshifted 21-cm line with SKA will provide a new and unique window on the entire period of Cosmic Dawn and Reionization. The signal is sensitive to the emergence of the first stellar populations, radiation from growing massive black holes and the formation of larger groups of galaxies and bright quasars. At the same time it maps the distribution of most of the baryonic matter in the Universe. The study of the redshifted 21cm line will teach us fundamental new things about the earliest phases of structure formation and cosmology. It even has the potential to lead to the discovery of new physical phenomena. Here we present an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.The redshifted 21cm signal will be analyzed with different techniques, which each come with their own requirements for the SKA: (i) Tomography, (ii) power-spectra and higher-order statistics, (iii) hydrogen absorption, (iv) global/total-intensity signal. Whereas all precursors/pathfinders aim to study the signal statistically through its power spectrum, SKA will be able to image the neutral hydrogen distribution directly and its focus will therefore be more on tomograph...

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Section: Removalmentioning

confidence: 99%

Section: Removalmentioning

confidence: 99%

Reionization and the Cosmic Dawn with the Square Kilometre Array

et al. 2013

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“…In a recent paper, Chapman et al (2014) have compared different frequency window functions to conclude that the extended Blackman-Nuttall window is the best choice for recovering the HI power spectrum. For the present work we have used the Blackman-Nuttall window as given by eq.…”

Section: Frequency Window Functionmentioning

confidence: 99%

The visibility-based tapered gridded estimator (TGE) for the redshifted 21-cm power spectrum

Choudhuri¹,

Bharadwaj²,

Chatterjee³

et al. 2016

Mon. Not. R. Astron. Soc.

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We present the improved visibility based Tapered Gridded Estimator (TGE) for the power spectrum of the diffuse sky signal. The visibilities are gridded to reduce the computation, and tapered through a convolution to suppress the contribution from the outer regions of the telescope's field of view. The TGE also internally estimates the noise bias, and subtracts this out to give an unbiased estimate of the power spectrum. An earlier version of the 2D TGE for the angular power spectrum C ℓ is improved and then extended to obtain the 3D TGE for the power spectrum P (k) of the 21-cm brightness temperature fluctuations. Analytic formulas are also presented for predicting the variance of the binned power spectrum. The estimator and its variance predictions are validated using simulations of 150 MHz GMRT observations. We find that the estimator accurately recovers the input model for the 1D Spherical Power Spectrum P (k) and the 2D Cylindrical Power Spectrum P (k ⊥ , k ), and the predicted variance is also in reasonably good agreement with the simulations.

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“…The foregrounds are smooth along frequency in total intensity and might show fluctuations in polarized intensity. Therefore, the EoR signal can be extracted from the foreground emission by fitting out the smooth component of the foregrounds along frequency, as shown for the LOFAR case by Jelić et al (2008);Harker et al (2009);Chapman et al (2012Chapman et al ( , 2013.…”

Section: Foreground Emission In the Lofar-eor Experimentsmentioning

confidence: 99%

Initial LOFAR observations of epoch of reionization windows

Jelić

Bruyn

Mevius

et al. 2014

A&A

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Aims. This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray -Epoch of Reionization (LOFAR-EoR) data. Methods. We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results. The brightness temperature of the detected Galactic emission is on average ∼4 K in polarized intensity and covers the range from -10 to +13 rad m −2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies Conclusions. The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ∼1-2 rad m −2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.

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Foreground removal usingfastica: a showcase of LOFAR-EoR

Cited by 189 publications

References 50 publications

Reionization and the Cosmic Dawn with the Square Kilometre Array

Reionization and the Cosmic Dawn with the Square Kilometre Array

The visibility-based tapered gridded estimator (TGE) for the redshifted 21-cm power spectrum

Initial LOFAR observations of epoch of reionization windows

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