Abstract
We present a detection of 21 cm emission from large-scale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations ...acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1
σ
(LRG), 5.7
σ
(ELG), and 11.1
σ
(QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (H
i
), defined as
H
I
≡
10
3
Ω
H
I
b
H
I
+
〈
f
μ
2
〉
, where Ω
H
i
is the cosmic abundance of H
i
,
b
H
i
is the linear bias of H
i
, and 〈
f
μ
2
〉 = 0.552 encodes the effect of redshift-space distortions at linear order. We find
H
I
=
1.51
−
0.97
+
3.60
for LRGs (
z
= 0.84),
H
I
=
6.76
−
3.79
+
9.04
for ELGs (
z
= 0.96), and
H
I
=
1.68
−
0.67
+
1.10
for QSOs (
z
= 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δ
v
= − 66 ± 20 km s
−1
for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin at
z
= 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far.
Abstract We report the detection of 21 cm emission at an average redshift z ¯ = 2.3 in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements ...of the Ly α forest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 < z < 2.5) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales with k ∥ ≲ 0.13 Mpc −1 at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Ly α forest flux transmission spectra to estimate the 21 cm–Ly α cross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9 σ detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼6–10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and they set the stage for future 21 cm intensity mapping analyses at z > 1.8.
Abstract
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift scan radio telescope operating across the 400–800 MHz band. CHIME is located at the Dominion Radio Astrophysical ...Observatory near Penticton, BC, Canada. The instrument is designed to map neutral hydrogen over the redshift range 0.8–2.5 to constrain the expansion history of the universe. This goal drives the design features of the instrument. CHIME consists of four parallel cylindrical reflectors, oriented north–south, each 100 m × 20 m and outfitted with a 256-element dual-polarization linear feed array. CHIME observes a two-degree-wide stripe covering the entire meridian at any given moment, observing three-quarters of the sky every day owing to Earth’s rotation. An FX correlator utilizes field-programmable gate arrays and graphics processing units to digitize and correlate the signals, with different correlation products generated for cosmological, fast radio burst, pulsar, very long baseline interferometry, and 21 cm absorber back ends. For the cosmology back end, the
N
feed
2
correlation matrix is formed for 1024 frequency channels across the band every 31 ms. A data receiver system applies calibration and flagging and, for our primary cosmological data product, stacks redundant baselines and integrates for 10 s. We present an overview of the instrument, its performance metrics based on the first 3 yr of science data, and we describe the current progress in characterizing CHIME’s primary beam response. We also present maps of the sky derived from CHIME data; we are using versions of these maps for a cosmological stacking analysis, as well as for investigation of Galactic foregrounds.
Abstract
We present a beam pattern measurement of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) made using the Sun as a calibration source. As CHIME is a pure drift-scan instrument, we ...rely on the seasonal north–south motion of the Sun to probe the beam at different elevations. This semiannual range in elevation, combined with the radio brightness of the Sun, enables a beam measurement that spans ∼7200 square degrees on the sky without the need to move the telescope. We take advantage of observations made near solar minimum to minimize the impact of solar variability, which is observed to be <10% in intensity over the observation period. The resulting data set is highly complementary to other CHIME beam measurements—both in terms of angular coverage and systematics—and plays an important role in the ongoing program to characterize the CHIME primary beam.
There is paucity of data on the smoking habits of rural populations in developing countries. This study aimed to explore cigarette smoking practices of a rural community in Ethiopia.
A community ...based cross-sectional study was conducted among 548 individuals from a random sample of households in a rural town and its surrounding rural districts. Descriptive statistics and logistic regression were performed.
Twenty-eight percent (95% CI: 24.3% - 31.6%) of the respondents were current smokers. A total of 105 (68%) smokers expressed an interest to quit while 37 (34%) had tried to quit previously but without success. There was high exposure to second-hand smoke: 285 (52%) homes allowed indoor smoking, and in 181 (33%) indoor smoking took place daily. Current smoking was strongly associated with male sex (OR = 83.0; 95% CI: 11.5 - 599.0), and being a student was found to be protective of smoking (OR = 0.04; 95% CI: 0.005 - 0.05).
Cigarette smoking is prevalent among the male rural town population in Ethiopia. In addition, a high level of exposure to indoor second-hand smoke exists. There is a need for investment in rural tobacco control, including educational campaigns and cost-effective smoking cessation services.
Ethiopia has been characterized by high population growth. Recent
social and economic developments have the potential to alter
reproductive patterns in the country. Some of these developments
include ...sustained economic growth, urbanization, rapid growth in school
enrollments, expansion of primary health care, and a rise in
contraceptive access and use. In other national contexts, these
developments have been associated with a gradual decoupling of the
transition into sexual activity and marriage among young women. We
investigate recent trends in the transition into first sex and marriage
among three cohorts of Ethiopian women. Methods: Using data from the
2000, 2005, and 2011 Ethiopia Demographic and Health Surveys (DHS) we
estimate survival curves and discrete-time hazards models to examine
recent trends in age at first sex and first marriage among women ages
20-29. Results: Across the three survey years the median age at first
sex has remained relatively stable at 17 years, although the median age
at marriage has increased from 17 to 18 years between the 2005 and 2011
surveys. Net of the effects of education and place of residence, there
is evidence of a slight trend away from premarital first sex to sexual
initiation in the context of marriage. However, among the most educated
women and women living in urban areas (who are a small minority of
women), there is a much greater tendency to initiate sexual activity
outside of marriage compared to women with little schooling and women
living in rural areas, and once they have begun sexual activity they
tend to wait longer before they get married. We also find evidence in
the most recent survey that women who have first sexual intercourse
before marriage are delaying marriage more than was the case among
earlier cohorts.
We present beam measurements of the CHIME telescope using a radio calibration source deployed on a drone payload. During test flights, the pulsing calibration source and the telescope were ...synchronized to GPS time, enabling in-situ background subtraction for the full \(N^{2}\) visibility matrix for one CHIME cylindrical reflector. We use the autocorrelation products to estimate the primary beam width and centroid location, and compare these quantities to solar transit measurements and holographic measurements where they overlap on the sky. We find that the drone, solar, and holography data have similar beam parameter evolution across frequency and both spatial coordinates. This paper presents the first drone-based beam measurement of a large cylindrical radio interferometer. Furthermore, the unique analysis and instrumentation described in this paper lays the foundation for near-field measurements of experiments like CHIME.
We report the detection of 21 cm emission at an average redshift $\bar{z} =
2.3$ in the cross-correlation of data from the Canadian Hydrogen Intensity
Mapping Experiment (CHIME) with measurements of ...the Lyman-$\alpha$ forest from
eBOSS. Data collected by CHIME over 88 days in the $400-500$~MHz frequency band
($1.8 < z < 2.5$) are formed into maps of the sky and high-pass delay filtered
to suppress the foreground power, corresponding to removing cosmological scales
with $k_\parallel \lesssim 0.13\ \text{Mpc}^{-1}$ at the average redshift.
Line-of-sight spectra to the eBOSS background quasar locations are extracted
from the CHIME maps and combined with the Lyman-$\alpha$ forest flux
transmission spectra to estimate the 21 cm-Lyman-$\alpha$ cross-correlation
function. Fitting a simulation-derived template function to this measurement
results in a $9\sigma$ detection significance. The coherent accumulation of the
signal through cross-correlation is sufficient to enable a detection despite
excess variance from foreground residuals $\sim6-10$ times brighter than the
expected thermal noise level in the correlation function. These results are the
highest-redshift measurement of \tcm emission to date, and set the stage for
future 21 cm intensity mapping analyses at $z>1.8$.
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