80 research outputs found
Reionization and Beyond: detecting the peaks of the cosmological 21cm signal
[ABRIDGED] The cosmological 21cm signal is set to become the most powerful
probe of the early Universe, with first generation interferometers aiming to
make statistical detections of reionization. There is increasing interest also
in the pre-reionization epoch when the intergalactic medium was heated by an
early X-ray background. Here we perform parameter studies varying the halo
masses hosting galaxies, and their X-ray production efficiencies. We also
relate these to popular models of Warm Dark Matter cosmologies. For each
parameter combination we compute the signal-to-noise (S/N) of the large-scale
(k~0.1/Mpc) 21cm power for both reionization and X-ray heating for a 2000h
observation with several instruments: 128 tile Murchison Wide Field Array
(MWA128T), a 256 tile extension (MWA256T), the Low Frequency Array (LOFAR), the
128 element Precision Array for Probing the Epoch of Reionization (PAPER), and
the second generation Square Kilometre Array (SKA). We show that X-ray heating
and reionization in many cases are of comparable detectability. For fiducial
astrophysical parameters, MWA128T might detect X-ray heating thanks to its
extended bandpass. When it comes to reionization, both MWA128T and PAPER will
also only achieve marginal detections, unless foregrounds on larger scales can
be mitigated. On the other hand, LOFAR should detect plausible models of
reionization at S/N > 10. The SKA will easily detect both X-ray heating and
reionization.Comment: 13 pages, 10 figures, MNRAS in-pres
Detecting the 21 cm Forest in the 21 cm Power Spectrum
We describe a new technique for constraining the radio loud population of
active galactic nuclei at high redshift by measuring the imprint of 21 cm
spectral absorption features (the 21 cm forest) on the 21 cm power spectrum.
Using semi-numerical simulations of the intergalactic medium and a
semi-empirical source population we show that the 21 cm forest dominates a
distinctive region of -space, . By simulating
foregrounds and noise for current and potential radio arrays, we find that a
next generation instrument with a collecting area on the order of (such as the Hydrogen Epoch of Reionization Array) may
separately constrain the X-ray heating history at large spatial scales and
radio loud active galactic nuclei of the model we study at small ones. We
extrapolate our detectability predictions for a single radio loud active
galactic nuclei population to arbitrary source scenarios by analytically
relating the 21 cm forest power spectrum to the optical depth power spectrum
and an integral over the radio luminosity function.Comment: 20 pages, 17 figures, accepted for publication in MNRA
Effects of Antenna Beam Chromaticity on Redshifted 21~cm Power Spectrum and Implications for Hydrogen Epoch of Reionization Array
Unaccounted for systematics from foregrounds and instruments can severely
limit the sensitivity of current experiments from detecting redshifted 21~cm
signals from the Epoch of Reionization (EoR). Upcoming experiments are faced
with a challenge to deliver more collecting area per antenna element without
degrading the data with systematics. This paper and its companions show that
dishes are viable for achieving this balance using the Hydrogen Epoch of
Reionization Array (HERA) as an example. Here, we specifically identify
spectral systematics associated with the antenna power pattern as a significant
detriment to all EoR experiments which causes the already bright foreground
power to leak well beyond ideal limits and contaminate the otherwise clean EoR
signal modes. A primary source of this chromaticity is reflections in the
antenna-feed assembly and between structures in neighboring antennas. Using
precise foreground simulations taking wide-field effects into account, we
provide a framework to set cosmologically-motivated design specifications on
these reflections to prevent further EoR signal degradation. We show HERA will
not be impeded by such spectral systematics and demonstrate that even in a
conservative scenario that does not perform removal of foregrounds, HERA will
detect EoR signal in line-of-sight -modes, ~Mpc, with high significance. All baselines in a 19-element HERA
layout are capable of detecting EoR over a substantial observing window on the
sky.Comment: 11 pages, 6 figures (10 total including subfigures), submitted to Ap
Constraining High Redshift X-ray Sources with Next Generation 21 cm Power Spectrum Measurements
We use the Fisher matrix formalism and semi-numerical simulations to derive
quantitative predictions of the constraints that power spectrum measurements on
next-generation interferometers, such as the Hydrogen Epoch of Reionization
Array (HERA) and the Square Kilometre Array (SKA), will place on the
characteristics of the X-ray sources that heated the high redshift
intergalactic medium. Incorporating observations between and , we
find that the proposed 331 element HERA and SKA phase 1 will be capable of
placing constraints on the spectral properties of these first
X-ray sources, even if one is unable to perform measurements within the
foreground contaminated "wedge" or the FM band. When accounting for the
enhancement in power spectrum amplitude from spin temperature fluctuations, we
find that the observable signatures of reionization extend well beyond the peak
in the power spectrum usually associated with it. We also find that lower
redshift degeneracies between the signatures of heating and reionization
physics lead to errors on reionization parameters that are significantly
greater than previously predicted. Observations over the heating epoch are able
to break these degeneracies and improve our constraints considerably. For these
two reasons, 21\,cm observations during the heating epoch significantly enhance
our understanding of reionization as well.Comment: 15 pages, 10 figures, Accepted to MNRA
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
The Radio Scream from Black Holes at Cosmic Dawn: A Semi-Analytic Model for the Impact of Radio Loud Black-Holes on the 21 cm Global Signal
We use a semi-analytic model to explore the potential impact of a brief and violent period of radio-loud accretion on to black holes (The Radio Scream) during the Cosmic Dawn on the H I hyperfine 21 cm signal. We find that radio emission from supermassive black hole seeds can impact the global 21 cm signal at the level of tens to hundreds of per cent provided that they were as radio loud as z ≈ 1 black holes and obscured by gas with column depths of N_H ≳ 10²³cm⁻². We determine plausible sets of parameters that reproduce some of the striking features of the EDGES absorption feature including its depth, timing, and side steepness while producing radio/X-ray backgrounds and source counts that are consistent with published limits. Scenarios yielding a dramatic 21 cm signature also predict large populations of ∼μJy point sources that will be detectable in future deep surveys from the Square Kilometer Array (SKA). Thus, 21 cm measurements, complemented by deep point-source surveys, have the potential to constrain optimistic scenarios where supermassive black hole progenitors were radio loud
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