336 research outputs found
Constraining cosmology and ionization history with combined 21 cm power spectrum and global signal measurements
Improvements in current instruments and the advent of next-generation
instruments will soon push observational 21 cm cosmology into a new era, with
high significance measurements of both the power spectrum and the mean
("global") signal of the 21 cm brightness temperature. In this paper we use the
recently commenced Hydrogen Epoch of Reionization Array as a worked example to
provide forecasts on astrophysical and cosmological parameter constraints. In
doing so we improve upon previous forecasts in a number of ways. First, we
provide updated forecasts using the latest best-fit cosmological parameters
from the Planck satellite, exploring the impact of different Planck datasets on
21 cm experiments. We also show that despite the exquisite constraints that
other probes have placed on cosmological parameters, the remaining
uncertainties are still large enough to have a non-negligible impact on
upcoming 21 cm data analyses. While this complicates high-precision constraints
on reionization models, it provides an avenue for 21 cm reionization
measurements to constrain cosmology. We additionally forecast HERA's ability to
measure the ionization history using a combination of power spectrum
measurements and semi-analytic simulations. Finally, we consider ways in which
21 cm global signal and power spectrum measurements can be combined, and
propose a method by which power spectrum results can be used to train a compact
parameterization of the global signal. This parameterization reduces the number
of parameters needed to describe the global signal, increasing the likelihood
of a high significance measurement.Comment: 16 pages, 8 figures. Revised to match accepted MNRAS version:
expanded discussion of covariances between astrophysics and cosmology in
Section 2.2, including two new figures; short discussion relating to KL modes
added to Section 4; final results unchange
Redundant Array Configurations for 21 cm Cosmology
Realizing the potential of 21 cm tomography to statistically probe the
intergalactic medium before and during the Epoch of Reionization requires large
telescopes and precise control of systematics. Next-generation telescopes are
now being designed and built to meet these challenges, drawing lessons from
first-generation experiments that showed the benefits of densely packed, highly
redundant arrays--in which the same mode on the sky is sampled by many antenna
pairs--for achieving high sensitivity, precise calibration, and robust
foreground mitigation. In this work, we focus on the Hydrogen Epoch of
Reionization Array (HERA) as an interferometer with a dense, redundant core
designed following these lessons to be optimized for 21 cm cosmology. We show
how modestly supplementing or modifying a compact design like HERA's can still
deliver high sensitivity while enhancing strategies for calibration and
foreground mitigation. In particular, we compare the imaging capability of
several array configurations, both instantaneously (to address instrumental and
ionospheric effects) and with rotation synthesis (for foreground removal). We
also examine the effects that configuration has on calibratability using
instantaneous redundancy. We find that improved imaging with sub-aperture
sampling via "off-grid" antennas and increased angular resolution via far-flung
"outrigger" antennas is possible with a redundantly calibratable array
configuration.Comment: 19 pages, 11 figures. Revised to match the accepted ApJ versio
INCIDENTAL AND JOINT CONSUMPTION IN RECREATION DEMAND
A theory for analyzing incidental consumption in a single site recreation demand model is presented. We show that incidental consumption on a recreation trip, such as a visit to see friends or a visit to a second recreation site, can be treated as a complementary good and analyzed using conventional theory. We also show that the analysis applies whether the side trips are incidental or joint. In a simple application we find that failing to account for incidental consumption appears to create little bias in valuing recreation sites.Resource /Energy Economics and Policy,
Calibration of Low-Frequency, Wide-Field Radio Interferometers Using Delay/Delay-Rate Filtering
We present a filtering technique that can be applied to individual baselines
of wide-bandwidth, wide-field interferometric data to geometrically select
regions on the celestial sphere that contain primary calibration sources. The
technique relies on the Fourier transformation of wide-band frequency spectra
from a given baseline to obtain one-dimensional "delay images", and then the
transformation of a time-series of delay images to obtain two-dimensional
"delay/delay-rate images." Source selection is possible in these images given
appropriate combinations of baseline, bandwidth, integration time and source
location. Strong and persistent radio frequency interference (RFI) limits the
effectiveness of this source selection owing to the removal of data by RFI
excision algorithms. A one-dimensional, complex CLEAN algorithm has been
developed to compensate for RFI-excision effects. This approach allows CLEANed,
source-isolated data to be used to isolate bandpass and primary beam gain
functions. These techniques are applied to data from the Precision Array for
Probing the Epoch of Reionization (PAPER) as a demonstration of their value in
calibrating a new generation of low-frequency radio interferometers with wide
relative bandwidths and large fields-of-view.Comment: 17 pages, 6 figures, 2009AJ....138..219
Emulating Simulations of Cosmic Dawn for 21cm Power Spectrum Constraints on Cosmology, Reionization, and X-ray Heating
Current and upcoming radio interferometric experiments are aiming to make a
statistical characterization of the high-redshift 21cm fluctuation signal
spanning the hydrogen reionization and X-ray heating epochs of the universe.
However, connecting 21cm statistics to underlying physical parameters is
complicated by the theoretical challenge of modeling the relevant physics at
computational speeds quick enough to enable exploration of the high dimensional
and weakly constrained parameter space. In this work, we use machine learning
algorithms to build a fast emulator that mimics expensive simulations of the
21cm signal across a wide parameter space to high precision. We embed our
emulator within a Markov-Chain Monte Carlo framework, enabling it to explore
the posterior distribution over a large number of model parameters, including
those that govern the Epoch of Reionization, the Epoch of X-ray Heating, and
cosmology. As a worked example, we use our emulator to present an updated
parameter constraint forecast for the Hydrogen Epoch of Reionization Array
experiment, showing that its characterization of a fiducial 21cm power spectrum
will considerably narrow the allowed parameter space of reionization and
heating parameters, and could help strengthen Planck's constraints on
. We provide both our generalized emulator code and its
implementation specifically for 21cm parameter constraints as publicly
available software.Comment: 22 pages, 9 figures; accepted to Ap
Spectral Redundancy for Calibrating Interferometers and Suppressing the Foreground Wedge in 21\,cm Cosmology
Observations of 21\,cm line from neutral hydrogen promise to be an exciting
new probe of astrophysics and cosmology during the Cosmic Dawn and through the
Epoch of Reionization (EoR) to when dark energy accelerates the expansion of
the Universe. At each of these epochs, separating bright foregrounds from the
cosmological signal is a primary challenge that requires exquisite calibration.
In this paper, we present a new calibration method called \textsc{nucal} that
extends redundant-baseline calibration, allowing spectral variation in antenna
responses to be solved for by using correlations between visibilities measuring
the same angular Fourier modes at different frequencies. By modeling the
chromaticity of the beam-weighted sky with a tunable set of discrete prolate
spheroidal sequences (DPSS), we develop a calibration loop that optimizes for
spectrally smooth calibrated visibilities. Crucially, this technique does not
require explicit models of the sky or the primary beam. With simulations that
incorporate realistic source and beam chromaticity, we show that this method
solves for unsmooth bandpass features, exposes narrowband interference
systematics, and suppresses smooth-spectrum foregrounds below the level of
21\,cm reionization models, even within much of the so-called "wedge" region
where current foreground mitigation techniques struggle. We show that this
foreground subtraction can be performed with minimal cosmological signal loss
for certain well-sampled angular Fourier modes, making spectral-redundant
calibration a promising technique for current and next-generation 21\,cm
intensity mapping experiments.Comment: 22 pages, 10 figures, Submitted to MNRA
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