Peer-Reviewed Journal

Low Radio Frequency Observations from the Moon Enabled by NASA Landed Payload Missions

Anonymous — Mon, 08 Mar 2021 22:30:03 +0000

Low Radio Frequency Observations from the Moon Enabled by NASA Landed Payload Missions Anonymous (not verified) Mon, 03/08/2021 - 15:30

Authors: Jack O. Burns, Robert MacDowall, Stuart Bale, Gregg Hallinan, Neil Bassett and Alex Hegedus

Abstract: A new era of exploration of the low radio frequency universe from the Moon will soon be underway with landed payload missions facilitated by NASA's Commercial Lunar Payload Services (CLPS) program. CLPS landers are scheduled to deliver two radio science experiments, Radio wave Observations at the Lunar Surface of the photoElectron Sheath (ROLSES) to the nearside and Lunar Surface Electromagnetics Experiment (LuSEE) to the farside, beginning in 2021. These instruments will be pathfinders for a 10 km diameter interferometric array, Farside Array for Radio Science Investigations of the Dark ages and Exoplanets (FARSIDE), composed of 128 pairs of dipole antennas proposed to be delivered to the lunar surface later in the decade. ROLSES and LuSEE, operating at frequencies from ≈100 kHz to a few tens of megahertz, will investigate the plasma environment above the lunar surface and measure the fidelity of radio spectra on the surface. Both use electrically short, spiral-tube deployable antennas and radio spectrometers based upon previous flight models. ROLSES will measure the photoelectron sheath density to better understand the charging of the lunar surface via photoionization and impacts from the solar wind, charged dust, and current anthropogenic radio frequency interference. LuSEE will measure the local magnetic field and exo-ionospheric density, interplanetary radio bursts, Jovian and terrestrial natural radio emission, and the galactic synchrotron spectrum. FARSIDE, and its precursor risk-reduction six antenna-node array PRIME, would be the first radio interferometers on the Moon. FARSIDE would break new ground by imaging radio emission from coronal mass ejections (CME) beyond 2R⊙, monitor auroral radiation from the B-fields of Uranus and Neptune (not observed since Voyager), and detect radio emission from stellar CMEs and the magnetic fields of nearby potentially habitable exoplanets. Read the full paper on The Planetary Science Journal.

Jack O. Burns, Robert MacDowall, Stuart Bale, Gregg Hallinan, Neil Bassett and Alex Hegedus

Off

Traditional

White

Validation of EDGES Low-Band Antenna Beam Model

Anonymous — Sun, 28 Feb 2021 21:44:23 +0000

Validation of EDGES Low-Band Antenna Beam Model Anonymous (not verified) Sun, 02/28/2021 - 14:44

Authors: Nivedita Mahesh, Judd D. Bowman, Thomas J. Mozdzen, Alan E. E. Rogers, Raul A. Monsalve, Steven G. Murray, David Lewis

Abstract: The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the beam model of the low-band (50-100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes of numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated driftscan observation from an early EDGES low-band instrument that had a 10 m × 10 m ground plane, we find residual levels after fitting and removing a five-term foreground model to data binned in Local Sidereal Time (LST) average about 250 mK with 40 mK variation between numerical solvers. A similar analysis of the primary 30 m × 30 m sawtooth ground plane reduced the LST-averaged residuals to about 90 mK with ± 10 mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power which is within 4% of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that soil conductivity of 0.02 Sm −1 and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by Sutinjo et al. (2015) for the Murchison Radio-astronomy Observatory, where EDGES is located. Read more via the arVix.

Nivedita Mahesh, Judd D. Bowman, Thomas J. Mozdzen, Alan E. E. Rogers, Raul A. Monsalve, Steven G. Murray, David Lewis

Off

Traditional

White

Transformative Science from the Lunar Farside: Observations of the Dark Ages and Exoplanetary Systems at Low Radio Frequencies

Anonymous — Mon, 23 Nov 2020 17:37:48 +0000

Transformative Science from the Lunar Farside: Observations of the Dark Ages and Exoplanetary Systems at Low Radio Frequencies Anonymous (not verified) Mon, 11/23/2020 - 10:37

Author: Jack O. Burns

Abstract: The farside of the Moon is a pristine, quiet platform to conduct low radio frequency observations of the early Universe's Dark Ages, as well as space weather and magnetospheres associated with habitable exoplanets. In this paper, NASA-funded concept studies will be described including a lunar-orbiting spacecraft, DAPPER, that will measure the 21 cm global spectrum at redshifts 40-80, and an array of low frequency dipoles on the lunar farside surface, FARSIDE. DAPPER observations (17-38 MHz), using a single cross-dipole antenna, will measure the amplitude of the 21 cm spectrum to the level required to distinguish the standard {\Lambda}CDM cosmological model from those of additional cooling models possibly produced by exotic physics such as dark matter interactions. FARSIDE has a notional architecture consisting of 128 dipole antennas deployed across a 10 km area by a rover. FARSIDE would image the entire sky each minute in 1400 channels over 0.1-40 MHz. This would enable monitoring of the nearest stellar systems for the radio signatures of coronal mass ejections and energetic particle events, and would also detect the magnetospheres of the nearest candidate habitable exoplanets. In addition, FARSIDE would determine the Dark Ages global 21 cm signal at yet lower frequencies and provide a pathfinder for power spectrum measurements. Read more via the Philosophical Transactions of the Royal Society A online research articles.

Jack O. Burns

Off

Traditional

White

Quasi-equilibrium models of high-redshift disc galaxy evolution

Anonymous — Tue, 03 Nov 2020 17:02:01 +0000

Quasi-equilibrium models of high-redshift disc galaxy evolution Anonymous (not verified) Tue, 11/03/2020 - 10:02

Author: Steven R. Furlanetto

Abstract: In recent years, simple models of galaxy formation have been shown to provide reasonably good matches to available data on high-redshift luminosity functions. However, these prescriptions are primarily phenomenological, with only crude connections to the physics of galaxy evolution. Here we introduce a set of galaxy models that are based on a simple physical framework but incorporate more sophisticated models of feedback, star formation, and other processes. We apply these models to the high-redshift regime, showing that most of the generic predictions of the simplest models remain valid. In particular, the stellar mass--halo mass relation depends almost entirely on the physics of feedback (and is thus independent of the details of small-scale star formation) and the specific star formation rate is a simple multiple of the cosmological accretion rate. We also show that, in contrast, the galaxy's gas mass is sensitive to the physics of star formation, although the inclusion of feedback-driven star formation laws significantly changes the naive expectations. While these models are far from detailed enough to describe every aspect of galaxy formation, they inform our understanding of galaxy formation by illustrating several generic aspects of that process, and they provide a physically-grounded basis for extrapolating predictions to faint galaxies and high redshifts currently out of reach of observations. If observations show violations from these simple trends, they would indicate new physics occurring inside the earliest generations of galaxies. Read more via the arVix.

Steven R. Furlanetto

Off

Traditional

White

Ensuring Robustness in Training Set Based Global 21-cm Cosmology Analysis

Anonymous — Mon, 02 Nov 2020 23:18:26 +0000

Ensuring Robustness in Training Set Based Global 21-cm Cosmology Analysis Anonymous (not verified) Mon, 11/02/2020 - 16:18

Authors: Neil Bassett, David Rapetti, Keith Tauscher, Jack Burns, Joshua Hibbard

Abstract: We present a methodology for ensuring the robustness of our analysis pipeline in separating the global 21-cm hydrogen cosmology signal from large systematics based on singular value decomposition (SVD) of training sets. We show how traditional goodness-of-fit metrics such as the χ2 statistic that assess the fit to the full data may not be able to detect a suboptimal extraction of the 21-cm signal when it is fit alongside one or more additional components due to significant covariance between them. However, we find that comparing the number of SVD eigenmodes for each component chosen by the pipeline for a given fit to the distribution of eigenmodes chosen for synthetic data realizations created from training set curves can detect when one or more of the training sets is insufficient to optimally extract the signal. Furthermore, this test can distinguish which training set (e.g. foreground, 21-cm signal) needs to be modified in order to better describe the data and improve the quality of the 21-cm signal extraction. We also extend this goodness-of-fit testing to cases where a prior distribution derived from the training sets is applied and find that, in this case, the χ2 statistic as well as the recently introduced ψ2 statistic are able to detect inadequacies in the training sets due to the increased restrictions imposed by the prior. Crucially, the tests described in this paper can be performed when analyzing any type of observations with our pipeline. Read more via the arVix.

Neil Bassett, David Rapetti, Keith Tauscher, Jack Burns, Joshua Hibbard

Off

Traditional

White

Modelling the Galactic Foreground and Beam Chromaticity for Global 21-cm Cosmology

Anonymous — Sun, 01 Nov 2020 23:18:37 +0000

Modelling the Galactic Foreground and Beam Chromaticity for Global 21-cm Cosmology Anonymous (not verified) Sun, 11/01/2020 - 16:18

Authors: Joshua J. Hibbard, Keith Tauscher, David Rapetti, Jack O. Burns

Abstract: In order to characterize and model the beam-weighted foreground for global 21-cm signal experiments, we present a methodology for generating basis eigenvectors that combines analytical and observational models of both the galactic spectral index and sky brightness temperature with simulations of beams having various angular and spectral dependencies and pointings. Each combination creates a unique beam-weighted foreground. By generating eigenvectors to fit each foreground model using Singular Value Decomposition (SVD), we examine the effects of varying the components of the beam-weighted foreground. We find that the eigenvectors for modelling an achromatic, isotropic beam -- the ideal case -- are nearly identical regardless of the unweighted foreground model used, and are practicably indistinguishable from polynomial-based models. When anisotropic, chromatic beams weight the foreground, however, a coupling is introduced between the spatial and spectral structure of the foreground which distorts the eigenvectors away from the polynomial models and induces a dependence of the basis upon the exact features of the beam (chromaticity, pattern, pointing) and foreground (spectral index, sky brightness temperature map). We find that the beam has a greater impact upon the eigenvectors than foreground models. Any model which does not account for its distortion may produce RMS uncertainties on the order of ∼10 - 103 Kelvin for six-parameter, single spectrum fits. If the beam is incorporated directly using SVD and training sets, however, the resultant eigenvectors yield milli-Kelvin level uncertainties. Given a sufficiently detailed description of the sky, our methodology can be applied to any particular experiment with a suitably characterized beam for the purpose of generating accurate beam-weighted foreground models. Read more via the arVix.

Joshua J. Hibbard, Keith Tauscher, David Rapetti, Jack O. Burns

Off

Traditional

White

A Flexible Analytic Model of Cosmic Variance in the First Billion Years

Anonymous — Thu, 10 Sep 2020 22:40:00 +0000

A Flexible Analytic Model of Cosmic Variance in the First Billion Years Anonymous (not verified) Thu, 09/10/2020 - 16:40

Authors: A.C. Trapp, Steven R. Furlanetto

Abstract: Cosmic variance is the intrinsic scatter in the number density of galaxies due to fluctuations in the large-scale dark matter density field. In this work, we present a simple analytic model of cosmic variance in the high redshift Universe (z∼5−15). We assume that galaxies grow according to the evolution of the halo mass function, which we allow to vary with large-scale environment. Our model produces a reasonable match to the observed ultraviolet luminosity functions in this era by regulating star formation through stellar feedback and assuming that the UV luminosity function is dominated by recent star formation. We find that cosmic variance in the UVLF is dominated by the variance in the underlying dark matter halo population, and not by differences in halo accretion or the specifics of our stellar feedback model. We also find that cosmic variance dominates over Poisson noise for future high-z surveys except for the brightest sources or at very high redshifts (z≳12). We provide a linear approximation of cosmic variance for a variety of redshifts, magnitudes, and survey areas through the public Python package galcv. Finally, we introduce a new method for incorporating priors on cosmic variance into estimates of the galaxy luminosity function and demonstrate that it significantly improves constraints on that important observable. Read more via arXiv.

A.C. Trapp, Steven R. Furlanetto

Off

Traditional

White

Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits

Anonymous — Fri, 05 Jun 2020 16:20:22 +0000

Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits Anonymous (not verified) Fri, 06/05/2020 - 10:20

Authors: Keith Tauscher, David Rapetti, Jack O. Burns

Abstract: The assumptions inherent to global 21-cm signal analyses are rarely delineated. In this paper, we formulate a general list of suppositions underlying a given claimed detection of the global 21-cm signal. Then, we specify the form of these assumptions for two different analyses: 1) the one performed by the EDGES team showing an absorption trough in brightness temperature that they modeled separately from the sky foreground and 2) a new, so-called Minimum Assumption Analysis (MAA), that makes the most conservative assumptions possible for the signal. We show fits using the EDGES analysis on various beam-weighted foreground simulations from the EDGES latitude with no signal added. Depending on the beam used, these simulations produce large false troughs due to the invalidity of the foreground model to describe the combination of beam chromaticity and the shape of the Galactic plane in the sky, the residuals of which are captured by the ad hoc flattened Gaussian signal model. On the other hand, the MAA provides robust fits by including many spectra at different time bins and allowing any possible 21-cm spectrum to be modeled exactly. We present uncertainty levels and example signal reconstructions found with the MAA for different numbers of time bins. With enough time bins, one can determine the true 21-cm signal with the MAA to <10 times the noise level. Read more via arXiv.

Keith Tauscher, David Rapetti, Jack O. Burns

Off

Traditional

White

Characterizing the Radio Quiet Region Behind the Lunar Farside for Low Radio Frequency Experiments

Anonymous — Fri, 06 Mar 2020 22:03:40 +0000

Characterizing the Radio Quiet Region Behind the Lunar Farside for Low Radio Frequency Experiments Anonymous (not verified) Fri, 03/06/2020 - 15:03

Authors: Neil Bassett, David Rapetti, Jack O. Burns, Keith Tauscher, Robert MacDowall

Abstract: Low radio frequency experiments performed on Earth are contaminated by both ionospheric effects and radio frequency interference (RFI) from Earth-based sources. The lunar farside provides a unique environment above the ionosphere where RFI is heavily attenuated by the presence of the Moon. We present electrodynamics simulations of the propagation of radio waves around and through the Moon in order to characterize the level of attenuation on the farside. The simulations are performed for a range of frequencies up to 100 kHz, assuming a spherical lunar shape with an average, constant density. Additionally, we investigate the role of the topography and density profile of the Moon in the propagation of radio waves and find only small effects on the intensity of RFI. Due to the computational demands of performing simulations at higher frequencies, we propose a model for extrapolating the width of the quiet region above 100 kHz that also takes into account height above the lunar surface as well as the intensity threshold chosen to define the quiet region. This model, which we make publicly available through a Python package, allows the size of the radio quiet region to be easily calculated both in orbit or on the surface, making it directly applicable for lunar satellites as well as surface missions. Read more via arXiv.

Neil Bassett, David Rapetti, Jack O. Burns, Keith Tauscher, Robert MacDowall

Off

Traditional

White

Global 21-cm Signal Extraction from Foreground and Instrumental Effects II: Efficient and Self-Consistent Technique for Constraining Nonlinear Signal Models

Anonymous — Fri, 06 Dec 2019 17:42:31 +0000

Global 21-cm Signal Extraction from Foreground and Instrumental Effects II: Efficient and Self-Consistent Technique for Constraining Nonlinear Signal Models Anonymous (not verified) Fri, 12/06/2019 - 10:42

Authors: David Rapetti, Keith Tauscher, Jordan Mirocha, Jack O. Burns

Abstract: We present the completion of a data analysis pipeline that self-consistently separates global 21-cm signals from large systematics using a pattern recognition technique. In the first paper of this series, we obtain optimal basis vectors from signal and foreground training sets to linearly fit both components with the minimal number of terms that best extracts the signal given its overlap with the foreground. In this second paper, we utilize the spectral constraints derived in the first paper to calculate the full posterior probability distribution of any signal parameter space of choice. The spectral fit provides the starting point for a Markov Chain Monte Carlo (MCMC) engine that samples the signal without traversing the foreground parameter space. At each MCMC step, we marginalize over the weights of all linear foreground modes and suppress those with unimportant variations by applying priors gleaned from the training set. This method drastically reduces the number of MCMC parameters, augmenting the efficiency of exploration, circumvents the need for selecting a minimal number of foreground modes, and allows the complexity of the foreground model to be greatly increased to simultaneously describe many observed spectra without requiring extra MCMC parameters. Using two nonlinear signal models, one based on EDGES observations and the other on phenomenological frequencies and temperatures of theoretically expected extrema, we demonstrate the success of this methodology by recovering the input parameters from multiple randomly simulated signals at low radio frequencies (10-200 MHz), while rigorously accounting for realistically modeled beam-weighted foregrounds. Read more via arXiv.

David Rapetti, Keith Tauscher, Jordan Mirocha, Jack O. Burns

Off

Traditional

White