14 research outputs found
Improving constraints on the reionization parameters using 21-cm bispectrum
Radio interferometric experiments aim to constrain the reionization model
parameters by measuring the 21-cm signal statistics, primarily the power
spectrum. However the Epoch of Reionization (EoR) 21-cm signal is highly
non-Gaussian, and this non-Gaussianity encodes important information about this
era. The bispectrum is the lowest order statistic able to capture this inherent
non-Gaussianity. Here we are the first to demonstrate that bispectra for large
and intermediate length scales and for all unique -triangle shapes provide
tighter constraints on the EoR parameters compared to the power spectrum or the
bispectra for a limited number of shapes of -triangles. We use the Bayesian
inference technique to constrain EoR parameters. We have also developed an
Artificial Neural Network (ANN) based emulator for the EoR 21-cm power spectrum
and bispectrum which we use to remarkably speed up our parameter inference
pipeline. Here we have considered the sample variance and the system noise
uncertainties corresponding to hrs of SKA-Low observations for
estimating errors in the signal statistics. We find that using all unique
-triangle bispectra improves the constraints on parameters by a factor of
(depending on the stage of reionization) over the constraints that are
obtained using power spectrum alone.Comment: 27 pages, 9 figures, Accepted for publication in JCA
Synthetic Observations with the Square Kilometre Array (SKA) -- development towards an end-to-end pipeline
Detection of the redshifted 21-cm signal of neutral hydrogen from the Cosmic
Dawn and the Epoch of Reionization is one of the final frontiers of modern
observational cosmology. The inherently faint signal makes it susceptible to
contamination by several sources like astrophysical foregrounds and
instrumental systematics. Nevertheless, developments achieved in the recent
times will combine to make signal detection possible with the upcoming Square
Kilometer Array (SKA), both statistically and via tomography. This review
describes an indigenously developed end-to-end pipeline that simulates
sensitive interferometric observations. It mainly focuses on the requirements
for \hi detection in interferometers. In its present form, it can mimic the
effects of realistic point source foregrounds and systematics- calibration
error and position error on 21-cm observations. The performance of the pipeline
is demonstrated for test cases with 0.01\% calibration error and position
error. Its performance is consistent across telescope, foreground, and signal
models. The focus of the simulation pipeline during the initial stages was for
EoR science. But since this is a general interferometric simulation pipeline,
it will be helpful to the entire SKA user community, irrespective of the
science goals.Comment: 24 Pages, 7 Figures, Review Article to appear in Special Issue of
Journal of Astrophysics and Astronomy on "Indian Participation in the SKA'',
comments are welcom
Detailed study of the ELAIS N1 field with the uGMRT - I. Characterizing the 325 MHz foreground for redshifted 21 cm observations
In this first paper of the series, we present initial results of newly
upgraded Giant Meterwave Radio Telescope (uGMRT) observation of European
Large-Area ISO Survey-North 1 (ELAIS-N1) at 325 MHz with 32 MHz bandwidth.
Precise measurement of fluctuations in Galactic and extragalactic foreground
emission as a function of frequency as well as angular scale is necessary for
detecting redshifted 21-cm signal of neutral hydrogen from Cosmic Dawn, Epoch
of Reionization (EoR) and post-reionization epoch. Here, for the first time we
have statistically quantified the Galactic and extragalactic foreground sources
in the ELAIS-N1 field in the form of angular power spectrum using the newly
developed Tapered Gridded Estimator (TGE). We have calibrated the data with and
without direction-dependent calibration techniques. We have demonstrated the
effectiveness of TGE against the direction dependent effects by using higher
tapering of field of view (FoV). We have found that diffuse Galactic
synchrotron emission (DGSE) dominates the sky, after point source subtraction,
across the angular multipole range and for
direction-dependent and -independent calibrated visibilities respectively. The
statistical fluctuations in DGSE has been quantified as a power law of the form
. The best fitted
values of (A, ) are ( , ) and ( , ) for the two different calibration
approaches. For both the cases, the power law index is consistent with the
previous measurements of DGSE in other parts of sky.Comment: 13 pages, 5figures, 4 tables; accepted for publication in MNRA
Towards 21-cm Intensity Mapping at with uGMRT using the Tapered Gridded Estimator I: Foreground Avoidance
The post-reionization neutral hydrogen (HI) 21-cm intensity
mapping signal holds the potential to probe the large scale structures, study
the expansion history and constrain various cosmological parameters. Here we
apply the Tapered Gridded Estimator (TGE) to estimate
the power spectrum of the redshifted 21-cm signal using a sub-band drawn
from uGMRT Band 3 observations of European Large-Area ISO Survey-North 1
(ELAIS-N1). The TGE allows us to taper the sky response which suppresses the
foreground contribution from sources in the periphery of the telescope's field
of view. We apply the TGE on the measured visibility data to estimate the
multi-frequency angular power spectrum (MAPS) from which
we determine using maximum-likelihood which
naturally overcomes the issue of missing frequency channels (55 \% here). The
entire methodology is validated using simulations. For the data, using the
foreground avoidance technique, we obtain a upper limit of
for the 21-cm brightness
temperature fluctuation at . This corresponds
to , where and respectively denote the cosmic \HI mass density and the \HI bias
parameter. A previous work has analyzed of the same data at
, and reported and
at . The upper
limits presented here are still orders of magnitude larger than the expected
signal corresponding to and .Comment: 13 pages, 11 figures, accepted for publication in MNRA
Towards -cm intensity mapping at with uGMRT using the tapered gridded estimator III: Foreground removal
Neutral hydrogen (\ion{H}{i}) -cm intensity mapping (IM) is a promising
probe of the large-scale structures in the Universe. However, a few orders of
magnitude brighter foregrounds obscure the IM signal. Here we use the Tapered
Gridded Estimator (TGE) to estimate the multi-frequency angular power spectrum
(MAPS) from a bandwidth uGMRT Band
data at . In foregrounds remain
correlated across the entire range, whereas the -cm signal is
localized within (typically ).
Assuming the range to have minimal -cm signal, we
use in this range to model the foregrounds. This
foreground model is extrapolated to , and subtracted
from the measured . The residual
in the range is
used to constrain the -cm signal, compensating for the signal loss from
foreground subtraction. is found to be
noise-dominated without any trace of foregrounds. Using
we constrain the -cm brightness
temperature fluctuations , and obtain the upper limit
at . We
further obtain the upper limit
[\Omega_{\ion{H}{i}}b_{\ion{H}{i}}]_{\rm UL}\leq0.022 where
\Omega_{\ion{H}{i}} and b_{\ion{H}{i}} are the comoving \ion{H}{i} density
and bias parameters respectively. Although the upper limit is nearly times
larger than the expected -cm signal, it is times tighter over previous
works using foreground avoidance on the same data.Comment: Accepted for publication in MNRAS. 16 pages (including Appendix), 8
figures (plus 8 in Appendix), 5 Table
Detailed study of ELAIS N1 field with the uGMRT - II. Source properties and spectral variation of foreground power spectrum from 300-500 MHz observations
Understanding the low-frequency radio sky in depth is necessary to subtract foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the cosmic dawn, the epoch of reionization and the post-reionization era. In this second paper of the series, we present the upgraded Giant Metrewave Radio Telescope (uGMRT) observation of the ELAIS N1 field made at 300-500 MHz. The image covers an area of similar to 1.8 deg(2) and has a central background rms noise of similar to 15 mu Jy beam(-1). We present a radio source catalogue containing 2528 sources (with flux densities > 100 mu Jy) and normalized source counts derived from that. A detailed comparison of detected sources with previous radio observations is shown. We discuss flux-scale accuracy, positional offsets, spectral index distribution and correction factors in source counts. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study simulation. It shows a flattening below similar to 1 mJy that corresponds to a rise in populations of star-forming galaxies and radio-quiet active galactic nuclei. For the first time, we estimate the spectral characteristics of the angular power spectrum or multi-frequency angular power spectrum of diffuse Galactic synchrotron emission over a wide frequency bandwidth of 300-500 MHz from radio interferometric observations. This work demonstrates the improved capabilities of the uGMRT