Nicholas S. Kern
A5046214946- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Antenna Design and Optimization
- Radio Wave Propagation Studies
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Electromagnetic Compatibility and Measurements
- Superconducting and THz Device Technology
- Millimeter-Wave Propagation and Modeling
- Particle Accelerators and Free-Electron Lasers
- Soil Moisture and Remote Sensing
- Cosmology and Gravitation Theories
- Stellar, planetary, and galactic studies
- Computational Physics and Python Applications
- Astronomical Observations and Instrumentation
- Scientific Research and Discoveries
- Gyrotron and Vacuum Electronics Research
- Advanced Wireless Communication Techniques
- Pulsed Power Technology Applications
- Microwave Engineering and Waveguides
- Advanced Data Storage Technologies
- Astrophysics and Star Formation Studies
- Particle accelerators and beam dynamics
- Optical measurement and interference techniques
- Gamma-ray bursts and supernovae
Massachusetts Institute of Technology
2020-2025
University of California, Berkeley
2016-2024
University Hospital Frankfurt
2023
Goethe University Frankfurt
2023
Kavli Institute for Particle Astrophysics and Cosmology
2021
University of Michigan–Ann Arbor
2013-2017
Abstract The Astropy Project supports and fosters the development of open-source openly developed Python packages that provide commonly needed functionality to astronomical community. A key element is core package astropy , which serves as foundation for more specialized projects packages. In this article, we summarize features in recent major release, version 5.0, updates on Project. We then discuss supporting a broader ecosystem interoperable packages, including connections with several...
Abstract The Astropy Project supports and fosters the development of open-source openly developed Python packages that provide commonly needed functionality to astronomical community. A key element is core package astropy , which serves as foundation for more specialized projects packages. In this article, we an overview organization project summarize features in package, recent major release, version 2.0. We then describe infrastructure designed facilitate support a broader ecosystem...
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...
Abstract Current and upcoming radio interferometric experiments are aiming to make a statistical characterization of the high-redshift 21 cm fluctuation signal spanning hydrogen reionization X-ray heating epochs universe. However, connecting statistics underlying physical parameters is complicated by theoretical challenge modeling relevant physics at computational speeds quick enough enable exploration high-dimensional weakly constrained parameter space. In this work, we use machine learning...
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 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...
Abstract We use the sky-average spectrum measured by EDGES High-band (90–190 MHz) to constrain parameters of early galaxies independent absorption feature at 78 MHz reported Bowman et al. These represent traditional models cosmic dawn and epoch reionization produced with 21cmFAST simulation code. The considered are (1) UV ionizing efficiency ( ζ ); (2) minimum halo virial temperature hosting efficient star-forming <?CDATA ${T}_{\mathrm{vir}}^{\min }$?> (3) integrated soft-band X-ray...
ABSTRACT In 21-cm cosmology, precision calibration is key to the separation of neutral hydrogen signal from very bright but spectrally smooth astrophysical foregrounds. The Hydrogen Epoch Reionization Array (HERA), an interferometer specialized for cosmology and now under construction in South Africa, was designed be largely calibrated using self-consistency repeated measurements same interferometric modes. This technique, known as redundant-baseline resolves most internal degrees freedom...
Abstract We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch Reionization Array (HERA), which aims to measure cosmological 21 cm signal from Reionization. HERA is a drift-scan array with 10° wide field view, meaning bright, well-characterized point-source transits are scarce. This, combined HERA’s redundant sampling uv plane and modest angular resolution instrument, make traditional sky-based self-calibration techniques difficult implement high dynamic range....
Radio Frequency Interference (RFI) is an ever-present limiting factor among radio telescopes even in the most remote observing locations. When looking to retain maximum amount of sensitivity and reduce contamination for Epoch Reionization studies, identification removal RFI especially important. In addition improved identification, we must also take into account computational efficiency RFI-Identification algorithm as interferometer arrays such Hydrogen Array grow larger number receivers. To...
ABSTRACT The detection of the Epoch Reionization (EoR) delay power spectrum using a ‘foreground avoidance method’ highly depends on instrument chromaticity. systematic effects induced by radio telescope spread foreground signal in domain, which contaminates EoR window theoretically observable. Applied to Hydrogen Array (HERA), this paper combines detailed electromagnetic and electrical simulations order model chromatic instrument, quantify its frequency time responses. In particular,...
We describe the validation of HERA Phase I software pipeline by a series modular tests, building up to an end-to-end simulation. The philosophy this approach is validate and algorithms used in upper limit analysis on wholly synthetic data satisfying assumptions that analysis, not addressing whether actual meet these assumptions. discuss organization approach, specific tests performed, construction simulations. explicitly limitations scope current simulation effort. With mock visibility...
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...
We quantify the expected observed statistical and systematic uncertainties of escape velocity as a measure gravitational potential total mass galaxy clusters. focus our attention on low redshift (z ⩽0.15) clusters, where large deep spectroscopic datasets currently exist. Utilizing suite Millennium Simulation semi-analytic catalogs, we find that dynamical mass, traced by either virial relation or velocity, is robust to variations in how friction applied "orphan" galaxies mock catalogs (i.e.,...
21 cm cosmology is a promising new probe of the evolution visible matter in our universe, especially during poorly-constrained Cosmic Dawn and Epoch Reionization. However, order to separate signal from bright astrophysical foregrounds, we need an exquisite understanding telescopes so as avoid adding spectral structure spectrally-smooth foregrounds. One powerful calibration method relies on repeated simultaneous measurements same interferometric baseline solve for sky instrumental parameters...
One of the primary challenges in enabling scientific potential 21 cm intensity mapping at Epoch Reionization (EoR) is separation astrophysical foreground contamination. Recent works have claimed that Gaussian process regression (GPR) can robustly perform this separation, particularly low Fourier $k$ wavenumbers where signal reaches its peak signal-to-noise ratio. We revisit topic by casting GPR subtraction (GPR-FS) into quadratic estimator formalism, thereby putting statistical properties on...
We introduce DAYENU, a linear, spectral filter for HI intensity mapping that achieves the desirable foreground mitigation and error minimization properties of inverse co-variance weighting with minimal modeling underlying data. Beyond 21 cm power-spectrum estimation, our is suitable any analysis where high dynamic-range removal spectrally smooth foregrounds in irregularly (or regularly) sampled data required, something required by many other techniques. Our filtering matrix diagonalized...
ABSTRACT Precision antenna calibration is required for mitigating the impact of foreground contamination in 21 cm cosmological radio surveys. One widely studied source error effect missing point sources sky model; however, poorly understood diffuse galactic emission also creates a bias that can complicate clean separation foregrounds from signal. In this work, we present technique suppressing with temporal filtering interferometric visibilities observed drift-scan mode. We demonstrate on...
The key challenge in the observation of redshifted 21-cm signal from cosmic reionization is its separation much brighter foreground emission. Such relies on different spectral properties two components, although, real life, intrinsic spectrum often corrupted by instrumental response, inducing systematic effects that can further jeopardize measurement signal. In this paper, we use Gaussian Process Regression to model both emission and systematics $\sim 2$ hours data Hydrogen Epoch...
Radio Frequency Interference (RFI) is one of the systematic challenges preventing 21cm interferometric instruments from detecting Epoch Reionization. To mitigate effects RFI on data analysis pipelines, numerous inpaint techniques have been developed to restore corrupted data. We examine qualitative and quantitative errors introduced into visibilities power spectrum due inpainting. perform our simulated as well real Hydrogen Reionization Array (HERA) Phase 1 upper limits. also introduce a...
Characterizing the epoch of reionization (EoR) at z≳6 via redshifted 21 cm line neutral Hydrogen (H i) is critical to modern astrophysics and cosmology, thus a key science goal many current planned low-frequency radio telescopes. The primary challenge detecting this signal overwhelmingly bright foreground emission these frequencies, placing stringent requirements on knowledge instruments inaccuracies in analyses. Results from experiments have largely been limited not by thermal sensitivity...
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...