18 research outputs found
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
PAPER-64 Constraints On Reionization II: The Temperature Of The z=8.4 Intergalactic Medium
We present constraints on both the kinetic temperature of the intergalactic
medium (IGM) at z=8.4, and on models for heating the IGM at high-redshift with
X-ray emission from the first collapsed objects. These constraints are derived
using a semi-analytic method to explore the new measurements of the 21 cm power
spectrum from the Donald C. Backer Precision Array for Probing the Epoch of
Reionization (PAPER), which were presented in a companion paper, Ali et al.
(2015). Twenty-one cm power spectra with amplitudes of hundreds of mK^2 can be
generically produced if the kinetic temperature of the IGM is significantly
below the temperature of the Cosmic Microwave Background (CMB); as such, the
new results from PAPER place lower limits on the IGM temperature at z=8.4.
Allowing for the unknown ionization state of the IGM, our measurements find the
IGM temperature to be above ~5 K for neutral fractions between 10% and 85%,
above ~7 K for neutral fractions between 15% and 80%, or above ~10 K for
neutral fractions between 30% and 70%. We also calculate the heating of the IGM
that would be provided by the observed high redshift galaxy population, and
find that for most models, these galaxies are sufficient to bring the IGM
temperature above our lower limits. However, there are significant ranges of
parameter space that could produce a signal ruled out by the PAPER
measurements; models with a steep drop-off in the star formation rate density
at high redshifts or with relatively low values for the X-ray to star formation
rate efficiency of high redshift galaxies are generally disfavored. The PAPER
measurements are consistent with (but do not constrain) a hydrogen spin
temperature above the CMB temperature, a situation which we find to be
generally predicted if galaxies fainter than the current detection limits of
optical/NIR surveys are included in calculations of X-ray heating.Comment: companion paper to Ali et al. (2015), ApJ 809, 61; matches version
accepted to ApJ; 11 pages, 7 figure
PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM AT z = 8.4
In this paper, we report new limits on 21 cm emission from cosmic reionization based on a 135 day observing campaign with a 64-element deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization in South Africa. This work extends the work presented in Parsons et al. with more collecting area, a longer observing period, improved redundancy-based calibration, improved fringe-rate filtering, and updated power-spectral analysis using optimal quadratic estimators. The result is a new 2σ upper limit on Δ[superscript 2](k) of (22.4 mK)[superscript 2] in the range 0.15 < k < 0.5h Mpc[superscript -1] at z = 8.4. This represents a three-fold improvement over the previous best upper limit. As we discuss in more depth in a forthcoming paper, this upper limit supports and extends previous evidence against extremely cold reionization scenarios. We conclude with a discussion of implications for future 21 cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array