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      Upper limits on the 21-cm Epoch of Reionization power spectrum from one night with LOFAR

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          Abstract

          We present the first limits on the Epoch of Reionization (EoR) 21-cm HI power spectra, in the redshift range \(z=7.9-10.6\), using the Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total 13\,h of data were used from observations centred on the North Celestial Pole (NCP). After subtraction of the sky model and the noise bias, we detect a non-zero \(\Delta^2_{\rm I} = (56 \pm 13 {\rm mK})^2\) (1-\(\sigma\)) excess variance and a best 2-\(\sigma\) upper limit of \(\Delta^2_{\rm 21} < (79.6 {\rm mK})^2\) at \(k=0.053\)$h\(cMpc\)^{-1}\( in the range \)z=$9.6-10.6. The excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. It is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to non-linear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. Further analyses of the excess variance will be discussed in forthcoming publications.

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          Morphological Component Analysis: An Adaptive Thresholding Strategy

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            Sparsity and morphological diversity in blind source separation.

            Over the last few years, the development of multichannel sensors motivated interest in methods for the coherent processing of multivariate data. Some specific issues have already been addressed as testified by the wide literature on the so-caIled blind source separation (BSS) problem. In this context, as clearly emphasized by previous work, it is fundamental that the sources to be retrieved present some quantitatively measurable diversity. Recently, sparsity and morphological diversity have emergedas a novel and effective source of diversity for BSS. Here, we give some new and essential insights into the use of sparsity in source separation, and we outline the essential role of morphological diversity as being a source of diversity or contrast between the sources. This paper introduces a new BSS method coined generalized morphological component analysis (GMCA) that takes advantages of both morphological diversity and sparsity, using recent sparse overcomplete or redundant signal representations. GMCA is a fast and efficient BSS method. We present arguments and a discussion supporting the convergence of the GMCA algorithm. Numerical results in multivariate image and signal processing are given illustrating the good performance of GMCA and its robustness to noise.
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              The Dark Ages of the Universe and Hydrogen Reionization

              One of the milestones in the cosmic history is the formation of the first luminous objects and Hydrogen reionization. The standard theory of cosmic structure formation predicts that the first generation of stars were born about a few hundred million years after the Big Bang. The dark Universe was then lit up once again, and eventually filled with ultraviolet photons emitted from stars, galaxies, and quasars. The exact epoch of the cosmic reionization and the details of the process, even the dominant sources, are not known except the fact that the universe was reionized early on. Signatures of reionization are expected to be imprinted in the cosmic microwave background radiation, especially in its large scale polarization. Future CMB experiments, together with other probes such as 21 cm surveys, will provide rich information on the process of reionization. We review recent studies on reionization. The implications from available observations in a wide range of wavelengths are discussed. Results from state-of-the-art computer simulations are presented. Finally, we discuss prospects for exploring the first few hundred million years of the cosmic history.
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                Author and article information

                Journal
                2017-02-28
                Article
                1702.08679
                513509b5-c24d-449b-bafc-aadfe920361e

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
                Custom metadata
                17 pages, 8 figures, accepted by ApJ
                astro-ph.CO astro-ph.IM

                Cosmology & Extragalactic astrophysics,Instrumentation & Methods for astrophysics

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