Joshua S. Dillon
A5024608470- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Antenna Design and Optimization
- Radio Wave Propagation Studies
- Superconducting and THz Device Technology
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Electromagnetic Compatibility and Measurements
- Millimeter-Wave Propagation and Modeling
- Soil Moisture and Remote Sensing
- Particle Accelerators and Free-Electron Lasers
- Computational Physics and Python Applications
- History and Developments in Astronomy
- Telecommunications and Broadcasting Technologies
- Advanced Wireless Communication Techniques
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Gyrotron and Vacuum Electronics Research
- Microwave Engineering and Waveguides
- Pulsed Power Technology Applications
- Optical measurement and interference techniques
- Superconducting Materials and Applications
- Gaussian Processes and Bayesian Inference
- Particle accelerators and beam dynamics
- Cosmology and Gravitation Theories
University of California, Berkeley
2016-2025
Massachusetts Institute of Technology
2013-2023
Berkeley College
2019
W.M. Keck Observatory
2017
Kavli Institute for Particle Astrophysics and Cosmology
2015-2016
International Centre for Radio Astronomy Research
2016
Curtin University
2016
University of California, Los Angeles
2014
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and explore earlier epochs our Cosmic Dawn ($z\sim30$). During these epochs, early stars black holes heated ionized IGM, introducing fluctuations in emission. HERA designed characterize evolution power spectrum constrain timing morphology reionization, properties first galaxies, large-scale structure,...
A number of experiments are currently working toward a measurement the 21 cm signal from epoch reionization (EoR). Whether or not these deliver detection cosmological emission, their limited sensitivity will prevent them providing detailed information about astrophysics reionization. In this work, we consider what types measurements be enabled by next generation larger EoR telescopes. To calculate type constraints that possible with such arrays, use simple models for instrument, foreground...
The Murchison Widefield Array (MWA) has collected hundreds of hours Epoch Reionization (EoR) data and now faces the challenge overcoming foreground systematic contamination to reduce a cosmological measurement. We introduce several novel analysis techniques such as cable reflection calibration, hyper-resolution gridding kernels, diffuse model subtraction, quality control methods. Each change pipeline is tested against two dimensional power spectrum figure merit demonstrate improvement....
Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights data (∼36 hr integration) from Phase I Hydrogen Array (HERA). The show evidence for systematics that can be largely suppressed systematic models down to a dynamic range ∼10 9 respect peak foreground power. This yields 95% confidence limit <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi...
Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced experiment’s first upper limits on power spectrum 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints intergalactic medium (IGM) galaxies during epoch reionization from these limits. We find that IGM must have been heated above adiabatic-cooling threshold by 8, uncertainties about ionization radio background. Combining HERA with complementary observations...
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...
We present techniques for bridging the gap between idealized inverse covariance weighted quadratic estimation of 21 cm power spectra and real-world challenges presented universally by interferometric observation. By carefully evaluating various estimators adapting our large but incomplete data sets, we develop a robust spectrum framework that preserves so-called "Epoch Reionization (EoR) window" keeps track estimator errors covariances. apply method to observations from 32-tile prototype...
We present an improved Global Sky Model (GSM) of diffuse Galactic radio emission from 10 MHz to 5 THz, whose uses include foreground modelling for cosmic microwave background (CMB) and 21 cm cosmology. Our model improves on past work both algorithmically by adding new data sets such as the Planck maps enhanced Haslam map. method generalizes principal component analysis approach handle non-overlapping regions, enabling inclusion 29 sky with no region common all. also perform a blind...
The Murchison Widefield Array (MWA) is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations future Square Kilometre (SKA). We describe automated radio-frequency interference (RFI) detection strategy implemented for MWA, which based on AOFlagger platform, and present 72-231-MHz RFI statistics from 10 observing nights. removes 1.1% data. digital TV (DTV) observed 3% time due to occasional ionospheric or atmospheric propagation. After excision,...
The separation of the faint cosmological background signal from bright astrophysical foregrounds remains one most daunting challenges mapping high-redshift intergalactic medium with redshifted 21 cm line neutral hydrogen. Advances in and modeling diffuse point source have improved subtraction accuracy, but no scheme is perfect. Precisely quantifying errors error correlations due to missubtracted allows for both rigorous analysis power spectrum maximal isolation "EoR window" foreground...
Detection of the cosmological neutral hydrogen signal from Epoch Reionization, and estimation its basic physical parameters, is principal scientific aim many current low-frequency radio telescopes. Here we describe Cosmological HI Power Spectrum Estimator (CHIPS), an algorithm developed implemented with data Murchison Widefield Array (MWA), to compute two-dimensional spherically-averaged power spectrum brightness temperature fluctuations. The motivations for CHIPS are application realistic...
Detection of 21~cm emission HI from the epoch reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate signatures wide-field measurements and an all-sky model using delay spectrum technique that maps to object locations through signal delays between antenna pairs. demonstrate interferometric are inherently sensitive all scales, including largest angular owing nature measurements. These effects generic observations but shapes impact their amplitudes...
We present first results from radio observations with the Murchison Widefield Array seeking to constrain power spectrum of 21 cm brightness temperature fluctuations between redshifts 11.6 and 17.9 (113 75 MHz). 3 h were conducted over two nights significantly different levels ionospheric activity. use these data assess impact systematic errors at low frequency, including ionosphere radio-frequency interference, on a measurement. find that after 1–3 integration presented here, our...
We study the impact of sky-based calibration errors from source mismodelling on 21 cm power spectrum measurements with an interferometer and propose a method for suppressing their effects. While emission faint sources that are not accounted in catalogues is believed to be spectrally smooth, deviations true visibilities model not, due inherent chromaticity interferometer's sky response (the 'wedge'). Thus, unmodelled foregrounds, below confusion limit many instruments, introduce frequency...
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 report on the MIT Epoch of Reionization (MITEoR) experiment, a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve calibration precision and reduce cost high-sensitivity 3D mapping required for 21 cm cosmology. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated correlator reduction. demonstrate quantify power robustness redundancy scalability precision. find parameters precisely describe effect instrument...
We confirm our recent prediction of the "pitchfork" foreground signature in power spectra high-redshift 21 cm measurements where interferometer is sensitive to large-scale structure on all baselines. This due inherent response a wide-field instrument and characterized by enhanced from emission Fourier modes adjacent those considered be most cosmological H i signal. In paper, many signatures simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data,...
We present the 21 cm power spectrum analysis approach of Murchison Widefield Array Epoch Reionization project. In this paper, we compare outputs multiple pipelines for purpose validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration reduction are used to make on a fiducial night data. Comparing imaging stages highlights differences in calibration, foreground subtraction calculation. The spectra found using these different...
ABSTRACT Realizing the potential of 21 cm tomography to statistically probe intergalactic medium before and during Epoch Reionization requires large telescopes precise control systematics. Next-generation are now being designed built meet these challenges, drawing lessons from first-generation experiments that showed benefits densely packed, highly redundant arrays—in which same mode on sky is sampled by many antenna pairs—for achieving high sensitivity, calibration, robust foreground...
Experiments that pursue detection of signals from the Epoch Reionization (EoR) are relying on spectral smoothness source spectra at low frequencies. This article empirically explores effect foreground EoR experiments by measuring high-resolution full-polarization for 586 brightest unresolved sources in one Murchison Widefield Array (MWA) fields using 45 h observation. A novel peeling scheme is used to subtract 2500 visibilities with ionospheric and beam corrections, resulting deepest,...
Abstract The Epoch of Reionization (EoR) is an uncharted era in our universe’s history during which the birth first stars and galaxies led to ionization neutral hydrogen intergalactic medium. There are many experiments investigating EoR by tracing 21 cm line hydrogen. Because this signal very faint difficult isolate, it crucial develop analysis techniques that maximize sensitivity suppress contaminants data. It also imperative understand trade-offs between different methods their effects on...
We present a study of internal reflection and cross coupling systematics in Phase I the Hydrogen Epoch Reionization Array (HERA). In companion paper, we outlined mathematical formalism for such presented algorithms modeling removing them from data. this work, apply these techniques to data HERA's first observing season as method demonstration. The show evidence that, without removal, would hinder detection 21 cm power spectrum targeted EoR line-of-sight modes range 0.2 < k_parallel 0.5\ h^-1...
Hamiltonian Monte Carlo is a powerful algorithm for sampling from difficult-to-normalize posterior distributions. However, when the geometry of unfavorable, it may take many expensive evaluations target distribution and its gradient to converge mix. We propose neural transport (NeuTra) HMC, technique learning correct this sort unfavorable using inverse autoregressive flows (IAF), variational inference technique. The IAF trained minimize KL divergence an isotropic Gaussian warped posterior,...
Abstract We present limits on the 21 cm power spectrum from Epoch of Reionization using data 64 antenna configuration Donald C. Backer Precision Array for Probing (PAPER) analyzed through a pipeline independent previous PAPER analyses. Previously reported results have been found to contain significant signal loss. Several lossy steps pipelines not included in this analysis, namely delay-based foreground filtering, optimal fringe-rate and empirical covariance-based estimators. Steps that...
We develop and demonstrate an acceleration of the Liu Tegmark quadratic estimator formalism for inverse variance foreground subtraction power spectrum estimation in 21 cm tomography from $\mathcal{O}({N}^{3})$ to $\mathcal{O}(N\mathrm{log}N)$, where $N$ is number voxels data. This technique makes feasible megavoxel scale analysis necessary current upcoming radio interferometers by making only moderately restrictive assumptions about models survey geometry. exploit iterative Monte Carlo...