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.
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 $z>1.8$.
The following document describes pursued studies to understand the properties of radio frequency interference (RFI) which affects the quality of the data of the Canadian Hydrogen Intensity Mapping ...Experiment Pathfinder at the Dominion Radio Astronomy Observatory in Penticton, British Columbia. The Canadian Hydrogen Intensity Mapping Experiment is a challenging project aimed to trace large scale structure by observing the 21cm emission line of neutral hydrogen in the frequency spectrum 400-800MHz to research the nature of Dark Energy.
RFI is terrestrial signal caused by radio bands, TV stations, satellites etc. that produces unwanted disturbances in the frequency spectrum which adds power to the data. It represents a challenge to measure faint sources in the sky and we seek ways to identify it based on its statistical properties such as non-Gaussianity.
We have designed algorithms that aim to identify and flag RFI in our data.
Digital TV bands cause permanent corruption in the affected frequency bins and account for a 19% loss of bandwidth.
The 5 sigma threshold cut searches for time-varying RFI in each frequency bin. Outliers above 5 standard deviations are iteratively flagged but not all of the occurring RFI were recognized due to non-Gaussianity.
The median absolute deviation cut is a robust statistical method that uses sky data only. Identification of short-lived and long-lived RFI occurrences originating mainly from the sky has been successful.
A correlation coefficient algorithm uses a combination of a reference RFI antenna sensitive to the horizon and a sky antenna to find correlated signals that are significantly above expected thermal noise of the radiometer while disregarding correlation due to sky signal. RFI at the horizon is well recognized by this method.
Science, Faculty of
Physics and Astronomy, Department of
Graduate
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the 21 cm emission of astrophysical neutral hydrogen to probe large scale structure at redshifts z=0.8-2.5. However, detecting ...the 21 cm signal beneath substantially brighter foregrounds remains a key challenge. Due to the high dynamic range between 21 cm and foreground emission, an exquisite calibration of instrument systematics, notably the telescope beam, is required to successfully filter out the foregrounds. One technique being used to achieve a high fidelity measurement of the CHIME beam is radio holography, wherein signals from each of CHIME's analog inputs are correlated with the signal from a co-located reference antenna, the 26 m John A. Galt telescope, as the 26 m Galt telescope tracks a bright point source transiting over CHIME. In this work we present an analysis of several of the Galt telescope's properties. We employ driftscan measurements of several bright sources, along with background estimates derived from the 408 MHz Haslam map, to estimate the Galt system temperature. To determine the Galt telescope's beam shape, we perform and analyze a raster scan of the bright radio source Cassiopeia A. Finally, we use early holographic measurements to measure the Galt telescope's geometry with respect to CHIME for the holographic analysis of the CHIME and Galt interferometric data set.
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