Hugh Garsden
A5033543858- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Antenna Design and Optimization
- Adaptive optics and wavefront sensing
- Radio Wave Propagation Studies
- Stellar, planetary, and galactic studies
- Computational Physics and Python Applications
- Particle Accelerators and Free-Electron Lasers
- Superconducting and THz Device Technology
- Astronomy and Astrophysical Research
- Gyrotron and Vacuum Electronics Research
- Telecommunications and Broadcasting Technologies
- Astrophysics and Star Formation Studies
- Speech and Audio Processing
- Optical measurement and interference techniques
- Microwave Engineering and Waveguides
- Satellite Communication Systems
- Advanced Database Systems and Queries
- Pulsed Power Technology Applications
- Pulsars and Gravitational Waves Research
- Particle accelerators and beam dynamics
- Robotic Mechanisms and Dynamics
- Ultrasound Imaging and Elastography
- Precipitation Measurement and Analysis
University of Manchester
2023-2025
Queen Mary University of London
2021-2025
Winona State University
2024
Center for Astrophysics Harvard & Smithsonian
2015-2022
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2013-2015
CEA Paris-Saclay
2014-2015
Université Paris Cité
2013-2015
Astrophysique, Instrumentation et Modélisation
2014-2015
Centre National de la Recherche Scientifique
2013-2015
Institut de Recherche sur les Lois Fondamentales de l'Univers
2014-2015
Abstract We report the most sensitive upper limits to date on 21 cm epoch of reionization power spectrum using 94 nights observing with Phase I Hydrogen Epoch Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ 2 ( k = 0.34 h Mpc −1 ) ≤ 457 mK z 7.9 and 0.36 3496 10.4, an improvement by a factor 2.1 2.6, respectively. These are mostly consistent thermal noise over wide range after our data quality cuts, despite...
The Large-aperture Experiment to Detect the Dark Age (LEDA) was designed detect predicted O(100) mK sky-averaged absorption of cosmic microwave background by hydrogen in neutral pre- and intergalactic medium just after cosmological Age. spectral signature would be associated with emergence a diffuse Lyα from starlight during 'Cosmic Dawn'. Recently, Bowman et al. have reported detection this feature, an unexpectedly large amplitude 530 mK, centred at 78 MHz. Verification result independent...
Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components the sky brightness. Recovering original brightness distribution aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods Aims. Recent papers have established clear link between nature interferometry measurement "compressed sensing" (CS)...
The 21\,cm transition of neutral hydrogen is opening an observational window into the cosmic dawn universe---the epoch first star formation. We use 28\,hr data from Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) to place upper limits on spatial power spectrum emission at $z \approx 18.4$ ($\Delta_{21} \lesssim 10^4\,\text{mK}$), and within absorption feature reported by EDGES experiment (Bowman et al. 2018). In process we demonstrate application double Karhunen-Lo\`{e}ve...
Abstract This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometre pathfinder instrument, we also show number “case studies” that investigate systematics seen while system, which...
We present the highest-quality polarisation profiles to date of 16 non-recycled pulsars and four millisecond pulsars, observed below 200 MHz with LOFAR high-band antennas. Based on profiles, we perform an initial investigation expected observational effects resulting from propagation polarised emission in pulsar magnetosphere interstellar medium. The predictions magnetospheric birefringence have been tested using spectra pulse width fractional multifrequency data. derived offer only partial...
Abstract A host of new low-frequency radio telescopes seek to measure the 21 cm transition neutral hydrogen from early universe. These have potential directly probe star and galaxy formation at redshifts 20 ≳ z 7 but are limited by dynamic range they can achieve against foreground sources emission. Consequently, there is a growing demand for modern, high-fidelity maps sky frequencies below 200 MHz use in modeling removal. We describe wide-field imaging technique drift-scanning...
ABSTRACT The Large-aperture Experiment to detect the Dark Age (LEDA) was designed measure 21-cm signal from neutral hydrogen at Cosmic Dawn, z ≈ 15–30. Using observations made with 200 m diameter core of Owens Valley Radio Observatory Long Wavelength Array (OVRO–LWA), we present a 2D cylindrical spatial power spectrum for data 43.1–53.5 MHz (zmedian 28) incoherently integrated 4 h, and an analysis array sensitivity. Power foregrounds is localized ‘wedge’ within k⊥, $k_\parallel$ space. After...
Abstract The precise characterization and mitigation of systematic effects is one the biggest roadblocks impeding detection fluctuations cosmological 21 cm signals. Missing data in radio experiments, often due to frequency interference (RFI), pose a particular challenge power spectrum analysis as this could lead ringing bright foreground modes Fourier space, heavily contaminating Here we show that problem missing becomes even more arduous presence effects. Using realistic numerical...
ABSTRACT Detection of the faint 21 cm line emission from Cosmic Dawn and Epoch Reionization will require not only exquisite control over instrumental calibration systematics to achieve necessary dynamic range observations but also validation analysis techniques demonstrate their statistical properties signal loss characteristics. A key ingredient in achieving this is ability perform high-fidelity simulations kinds data that are produced by large, many-element, radio interferometric arrays...
Abstract The Evolutionary Map of the Universe (EMU) is a proposed radio continuum survey Southern Hemisphere up to declination + 30°, with Australian Square Kilometre Array Pathfinder (ASKAP). EMU will use an automated source identification and measurement approach that demonstrably optimal, maximise reliability robustness resulting catalogues. As step toward this goal we conducted “Data Challenge” test variety finders on simulated images. aim quantify accuracy limitations existing finding...
Radio interferometer arrays such as HERA consist of many close-packed dishes arranged in a regular pattern, giving rise to large number `redundant' baselines with the same length and orientation. Since identical should see an sky signal, this provides way finding relative gain/bandpass calibration without needing explicit model. In reality, there are reasons why will not be exactly identical, host effects that spoil redundancy array induce spurious structure solutions if accounted for....
Radio astronomy observatories with high throughput back end instruments require real-time data processing. While computing hardware continues to advance rapidly, development of processing pipelines remains difficult and time-consuming, which can limit scientific productivity. Motivated by this, we have developed Bifrost: an open-source software framework for rapid pipeline development. (a) Bifrost combines a high-level Python interface highly efficient reconfigurable transport library blocks...
Cosmic Dawn, the onset of star formation in early universe, can principle be studied via 21cm transition neutral hydrogen, for which a sky-averaged absorption signal, redshifted to MHz frequencies, is predicted {\it O}(10-100)\,mK. Detection requires separation signal from bright chromatic foreground emission due Galactic structure, and characterisation how it couples instrumental response. In this work, we present antenna gain patterns Large-aperture Experiment detect Dark Ages (LEDA)...
ABSTRACT Power spectrum estimators are an important tool in efforts to detect the 21 cm brightness temperature fluctuations from neutral hydrogen at early times. An initial detection will likely be statistical nature, meaning that it not possible make a coherent map of fluctuations; instead, only their variance measured against background noise and residual systematic effects. Optimal quadratic estimator-based methods often apply inverse covariance weighting data. However, inaccurate...
Total-power radiometry with individual meter-wave antennas is a potentially effective way to study the Cosmic Dawn ($z\sim20$) through measurement of sky brightness arising from $21$~cm transition neutral hydrogen, provided this can be disentangled much stronger Galactic and extra-galactic foregrounds. In process, measured spectra integrated temperature used quantify foreground emission properties. work, we analyze subset data Large-aperture Experiment Detect Dark Age (LEDA) in range...
Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order signal, and simulations reproduce effects seen data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of Hydrogen Epoch Reionization Array compare against include...
The 21 cm transition from neutral Hydrogen promises to be the best observational probe of Epoch Reionisation (EoR). This has led construction low-frequency radio interferometric arrays, such as Reionization Array (HERA), aimed at systematically mapping this emission for first time. Precision calibration, however, is a requirement in observations. Due spatial compactness HERA, array prone effects mutual coupling, which inevitably lead non-smooth calibration errors that contaminate data. When...
Compressed sensing theory is slowly making its way to solve more and astronomical inverse problems. We address here the application of sparse representations, convex optimization proximal radio interferometric imaging. First, we expose behind imaging, representations optimization, second, illustrate their with numerical tests SASIR, an implementation FISTA, a Forward-Backward splitting algorithm hosted in LOFAR imager. Various have been conducted Garsden et al., 2015. The main results are:...
This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometer (SKA) pathfinder instrument, we also show number "case studies" that investigate systematics seen while system, which may...
Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters in fringe-rate (FR) space, pair local sidereal time (LST). Applications FR filtering include separating correlated with rotating sky vs. those relative ground, down-weighting emission primary beam sidelobes, and suppressing noise. causes noise...
ABSTRACT Accurate modelling of the primary beam is an important but difficult task in radio astronomy. For high dynamic range problems such as 21 cm intensity mapping, small errors sidelobes, and spectral structure beams can translate into significant systematic errors. Realistic exhibit complex spatial structure, presenting a major challenge for measurement calibration methods. In this paper series, we present Bayesian framework to infer per-element patterns from interferometric...