A5063221621- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Antenna Design and Optimization
- Astronomy and Astrophysical Research
- Scientific Research and Discoveries
- Soil Moisture and Remote Sensing
- Radio Wave Propagation Studies
- Cosmology and Gravitation Theories
- Direction-of-Arrival Estimation Techniques
- GNSS positioning and interference
- Superconducting and THz Device Technology
- Geophysics and Gravity Measurements
- Astronomical Observations and Instrumentation
- Microwave Engineering and Waveguides
- Precipitation Measurement and Analysis
- Gamma-ray bursts and supernovae
- Advanced Wireless Communication Techniques
- Millimeter-Wave Propagation and Modeling
- History and Developments in Astronomy
- Enhanced Oil Recovery Techniques
- Dark Matter and Cosmic Phenomena
- Minerals Flotation and Separation Techniques
- Speech and Audio Processing
- Blind Source Separation Techniques
University College London
2015-2017
Laboratory for Atmospheric and Space Physics
2011-2017
University of Groningen
2007-2017
Astronomical Institute of the Slovak Academy of Sciences
2009-2015
Astronomy and Space
2010-2015
University of Colorado Boulder
2010-2014
Ames Research Center
2010-2013
Solar System Exploration Research Virtual Institute
2010-2013
Durham University
2006-2007
We present the first limits on Epoch of Reionization 21 cm H i power spectra, in redshift range z = 7.9–10.6, using Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total, 13.0 hr data were used from observations centered North Celestial Pole. After subtraction sky model and noise bias, we detect a non-zero (1-σ) excess variance best 2-σ upper limit at k 0.053 h cMpc−1 9.6–10.6. The decreases when optimizing smoothness direction- frequency-dependent gain calibration, with increasing...
Future high redshift 21-cm experiments will suffer from a degree of contamination, due both to astrophysical foregrounds and non-astrophysical instrumental effects. In order reliably extract the cosmological signal observed data, it is essential understand very well all data components their influence on extracted signal. Here we present simulated datacubes discuss possible statistical effects data. The foreground maps are produced assuming 5 deg x windows that match those expected be by...
We study the environmental dependence of formation epoch dark matter haloes in Millennium Simulation: a ten billion particle N-body simulation standard LambdaCDM cosmology. A sensitive test this - marked correlation function reveals highly significant evidence that given mass form earlier denser regions. define cross-correlation function, which helps quantify how effect depends upon choice halo population used to environment. The mean redshift as local overdensity is also well determined,...
<i>Context. <i/>The cosmological 21 cm line promises to be a formidable tool for cosmology, allowing the investigation of end so-called dark ages, when first galaxies formed.<i>Aims. <i/>Astrophysical foregrounds are expected about three orders magnitude greater than signal and therefore represent serious contamination line. Detailed knowledge both their intensity polarization structure on relevant angular scale 1–30 arcmin will essential extracting from data.<i>Methods. <i/>We present...
We introduce a new implementation of the fastica algorithm on simulated Low Frequency Array Epoch Reionization data with aim accurately removing foregrounds and extracting 21-cm reionization signal. find that method successfully removes an average fitting error 0.5 per cent 2D 3D power spectra are recovered across frequency range. for scales above several point spread function scales, variance is though there evidence noise leakage into reconstructed foreground components. this blind...
The accurate and precise removal of 21-cm foregrounds from Epoch Reionization (EoR) redshifted emission data is essential if we are to gain insight into an unexplored cosmological era. We apply a non-parametric technique, Generalized Morphological Component Analysis (gmca), simulated Low Frequency Array (LOFAR)-EoR show that it has the ability clean with high accuracy. recover 1D, 2D 3D power spectra accuracy across impressive range frequencies scales. gmca preserves phase information,...
The aim of the LOFAR Epoch Reionization (EoR) project is to detect spectral fluctuations redshifted HI 21cm signal. This signal weaker by several orders magnitude than astrophysical foreground signals and hence, in order achieve this, very long integrations, accurate calibration for stations ionosphere reliable removal are essential. One prospective observing windows EoR will be centered at North Celestial Pole (NCP). We present results from observations NCP window using highband antenna...
One of the aims Low Frequency Array (LOFAR) Epoch Reionization (EoR) project is to measure power spectrum variations in intensity redshifted 21-cm radiation from EoR. The sensitivity with which this can be estimated depends on level thermal noise and sample variance, also systematic errors arising extraction process, particular subtraction foreground contamination. We model process using realistic simulations cosmological signal, foregrounds noise, so estimate LOFAR EoR experiment spectrum....
In the coming years a new insight into galaxy formation and thermal history of Universe is expected to come from detection highly redshifted cosmological 21 cm line. The line signal buried under Galactic extragalactic foregrounds which are likely be few orders magnitude brighter. Strategies techniques for effective subtraction these foreground sources require detailed knowledge their structure in both intensity polarization on relevant angular scales 1-30 arcmin. We present results...
This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) 3C196 field, one primary fields LOFAR-Epoch Reionization key science project. We have used high band antennas (HBA) image this region and Rotation Measure (RM) synthesis unravel distribution polarized Faraday depth. The brightness temperature detected Galactic emission is $5-15~{\rm K}$ intensity covers range from -3 +8 ${\rm rad~m^{-2}}$ most interesting morphological...
One of the most promising ways to study epoch reionization (EoR) is through radio observations redshifted 21-cm line emission from neutral hydrogen. These are complicated by fact that mapping redshifts line-of-sight positions distorted peculiar velocities gas. Such distortions can be a source error if they not properly understood, but also encode information about cosmology and astrophysics. We effects redshift space on power spectrum radiation EoR using large scale $N$-body radiative...
Aims. This paper discusses the spectral occupancy for performing radio astronomy with Low-Frequency Array (LOFAR), a focus on imaging observations.
This study aims to characterise the polarized foreground emission in ELAIS-N1 field and address its possible implications for extraction of cosmological 21-cm signal from Low-Frequency Array - Epoch Reionization (LOFAR-EoR) data. We use high band antennas LOFAR image this region RM-synthesis unravel structures at Galactic latitudes. The brightness temperature detected is on average 4 K intensity covers range -10 +13rad m^-2 Faraday depth. total polarization angle show a wide morphological...
Detection of the 21-cm signal coming from epoch reionization (EoR) is challenging especially because, even after removing foregrounds, residual Stokes I maps contain leakage polarized emission that can mimic signal. Here, we discuss instrumental polarization Low Frequency Array (LOFAR) and present realistic simulations leakages between parameters. From LOFAR observations in 3C196 field, have quantified level caused by nominal model beam LOFAR, compared it with EoR using power spectrum...
LOFAR is the LOw Frequency Radio interferometer ARray located at mid-latitude ($52^{\circ} 53'N$). Here, we present results on ionospheric structures derived from 29 nighttime observations during winters of 2012/2013 and 2013/2014. We show that able to determine differential TEC values with an accuracy better than 1 mTECU over distances ranging between 100 km. For all power law behavior phase structure function confirmed a long range baseline lengths, $1$ $80$ km, slope in general larger...
One of the problems facing experiments designed to detect redshifted 21-cm emission from epoch reionization (EoR) is presence foregrounds which exceed cosmological signal in intensity by orders magnitude. While fitting them so that they can be removed, we must careful minimize 'overfitting', fit away some signal, and 'underfitting', real features cannot captured fit, polluting reconstruction. We argue principle it would better non-parametrically – allowing data determine their shape rather...
We present an efficient method to generate large simulations of the epoch reionization without need for a full three-dimensional radiative transfer code. Large dark-matter-only are post-processed produce maps redshifted 21-cm emission from neutral hydrogen. Dark matter haloes embedded with sources radiation whose properties either based on semi-analytical prescriptions or derived hydrodynamical simulations. These could be stars power-law varying spectral indices. Assuming spherical symmetry,...
Several experiments are underway to detect the cosmic redshifted 21-cm signal from neutral hydrogen Epoch of Reionization (EoR). Due their very low signal-to-noise ratio, these observations aim for a statistical detection by measuring its power spectrum. We investigate extraction variance as first step towards detecting and constraining global history EoR. Signal is integral signal's spectrum, it expected be measured with high significance. demonstrate this through results simulation...
The first generation of redshifted 21 cm detection experiments, carried out with arrays like LOFAR, MWA and GMRT, will have a very low signal-to-noise ratio per resolution element (\sim 0.2). In addition, whereas the variance cosmological signal decreases on scales larger than typical size ionization bubbles, formidable galactic foregrounds increases, making it hard to disentangle two such large scales. poor sensitivity small one hand, effect other make direct imaging Epoch Reionization...