49 research outputs found
Foregrounds and their mitigation
The low-frequency radio sky is dominated by the diffuse synchrotron emission of our Galaxy and extragalactic radio sources related to Active Galactic Nuclei and star-forming galaxies. This foreground emission is much brighter than the cosmological 21 cm emission from the Cosmic Dawn and Epoch of Reionization. Studying the physical properties of the foregrounds is therefore of fundamental importance for their mitigation in the cosmological 21 cm experiments. This chapter gives a comprehensive overview of the foregrounds and our current state- of-the-art knowledge about their mitigation
The Effect of Foreground Mitigation Strategy on EoR Window Recovery
The removal of the Galactic and extragalactic foregrounds remains a major
challenge for those wishing to make a detection of the Epoch of Reionization
21-cm signal. Multiple methods of modelling these foregrounds with varying
levels of assumption have been trialled and shown promising recoveries on
simulated data. Recently however there has been increased discussion of using
the expected shape of the foregrounds in Fourier space to define an EoR window
free of foreground contamination. By carrying out analysis within this window
only, one can avoid the foregrounds and any statistical bias they might
introduce by instead removing these foregrounds. In this paper we discuss the
advantages and disadvantages of both foreground removal and foreground
avoidance. We create a series of simulations with noise levels in line with
both current and future experiments and compare the recovered statistical
cosmological signal from foreground avoidance and a simplified, frequency
independent foreground removal model. We find that while, for current
generation experiments, foreground avoidance enables a better recovery at
, foreground removal is able to recover
significantly more signal at small for both current and future
experiments. We also relax the assumption that the foregrounds are smooth by
introducing a Gaussian random factor along the line-of-sight and then also
spatially. We find that both methods perform well for foreground models with
line-of-sight and spatial variations around however at levels larger
than this foregrounds removal shows a greater signal recovery.Comment: 14 pages, 10 figures, accepted by MNRA
Magnetically aligned straight depolarization canals and the rolling Hough transform
Aims. We aim to characterize the properties of the straight depolarization canals detected in the Low Frequency Array (LOFAR) polarimetric observations of a field centered on the extragalactic source 3C 196. We also compare the canal orientations with magnetically aligned HI filaments and the magnetic field probed by polarized dust emission. Methods. We used the rolling Hough transform (RHT) to identify and characterize the orientation of the straight depolarization canals in radio polarimetric data and the filaments in HI data. Results. The majority of the straight depolarization canals and the Hi filaments are inclined by ~10° with respect to the Galactic plane and are aligned with the plane-of-sky magnetic field orientation probed by the Planck dust polarization data. The other distinct orientation, of −65° with respect to the Galactic plane, is associated with the orientation of a bar-like structure observed in the 3C 196 field at 350 MHz. Conclusions. An alignment between three distinct tracers of the (local) interstellar medium (ISM) suggests that an ordered magnetic field plays a crucial role in confining different ISM phases. The majority of the straight depolarization canals are a result of a projection of the complicated 3D distribution of the ISM. The RHT analysis is a robust method for identifying and characterizing the straight depolarization canals observed in radio-polarimetric data
Comparison of distance measurements to dust clouds using GRB X-ray halos and 3D dust extinction
X-ray photons from energetic sources such as gamma-ray bursts (GRBs) can be
scattered on dust clouds in the Milky Way, creating a time-evolving halo around
the GRB position. X-ray observations of such halos allow the measurement of
dust clouds distances in the Galaxy on which the scattering occurs. We present
the first systematic comparison of the distances to scattering regions derived
from GRB halos with the 3D dust distribution derived from recently published
optical-to-near infrared extinction maps. GRB halos were observed around 7
sources by the Swift XRT and the XMM-Newton EPIC instruments, namely GRB
031203, GRB 050713A, GRB 050724, GRB 061019, GRB 070129, GRB 160623A and GRB
221009A. We used four 3D extinction maps that exploit photometric data from
different surveys and apply diverse algorithms for the 3D mapping of
extinction, and compared the X-ray halo-derived distances with the local maxima
in the 3D extinction density distribution. We found that in all GRBs we can
find at least one local maximum in the 3D dust extinction map that is in
agreement with the dust distance measured from X-ray rings. For GRBs with
multiple X-ray rings, the dust distance measurements coincide with at least 3
maxima in the extinction map for GRB 160623A, and 5 maxima for GRB 221009A. The
agreement of these independent distance measurements shows that the methods
used to create dust extinction maps may potentially be optimized by the X-ray
halo observations from GRBs.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Predictions for the 21cm-galaxy cross-power spectrum observable with SKA and future galaxy surveys
In this paper, we use radiative transfer+N-body simulations to explore the feasibility of measurements of cross-correlations between the 21-cm field observed by the Square Kilometre Array (SKA) and high-z Lyman α emitters (LAEs) detected in galaxy surveys with the Subaru Hyper Suprime-Cam (HSC), Subaru Prime Focus Spectrograph (PFS), and Wide Field Infrared Survey Telescope (WFIRST). 21cm-LAE cross-correlations are in fact a powerful probe of the epoch of reionization as they are expected to provide precious information on the progress of reionization and the typical scale of ionized regions at different redshifts. The next generation observations with SKA will have a noise level much lower than those with its precursor radio facilities, introducing a significant improvement in the measurement of the cross-correlations. We find that an SKA-HSC/PFS observation will allow to investigate scales below ̃10 and ̃60 h-1 Mpc at z = 7.3 and 6.6, respectively. WFIRST will allow to access also higher redshifts, as it is expected to observe spectroscopically ̃900 LAEs per deg2 and unit redshift in the range 7.5 ≤ z ≤ 8.5. Because of the reduction of the shot noise compared to HSC and PFS, observations with WFIRST will result in more precise cross- correlations and increased observable scales
Cosmic Dawn and Epoch of Reionization Foreground Removal with the SKA
The exceptional sensitivity of the SKA will allow observations of the Cosmic
Dawn and Epoch of Reionization (CD/EoR) in unprecedented detail, both
spectrally and spatially. This wealth of information is buried under Galactic
and extragalactic foregrounds, which must be removed accurately and precisely
in order to reveal the cosmological signal. This problem has been addressed
already for the previous generation of radio telescopes, but the application to
SKA is different in many aspects.
In this chapter we summarise the contributions to the field of foreground
removal in the context of high redshift and high sensitivity 21-cm
measurements. We use a state-of-the-art simulation of the SKA Phase 1
observations complete with cosmological signal, foregrounds and
frequency-dependent instrumental effects to test both parametric and
non-parametric foreground removal methods. We compare the recovered
cosmological signal using several different statistics and explore one of the
most exciting possibilities with the SKA --- imaging of the ionized bubbles.
We find that with current methods it is possible to remove the foregrounds
with great accuracy and to get impressive power spectra and images of the
cosmological signal. The frequency-dependent PSF of the instrument complicates
this recovery, so we resort to splitting the observation bandwidth into smaller
segments, each of a common resolution.
If the foregrounds are allowed a random variation from the smooth power law
along the line of sight, methods exploiting the smoothness of foregrounds or a
parametrization of their behaviour are challenged much more than non-parametric
ones. However, we show that correction techniques can be implemented to restore
the performances of parametric approaches, as long as the first-order
approximation of a power law stands.Comment: Accepted for publication in the SKA Science Book 'Advancing
Astrophysics with the Square Kilometre Array', to appear in 201
Detectability of the 21 cm-CMB cross-correlation from the EoR
The 21-cm line fluctuations and the cosmic microwave background (CMB) are
powerful probes of the epoch of reionisation of the universe. We study the
potential of the cross-correlation between 21-cm line fluctuations and CMB
anisotropy to obtain further constraints on the reionisation history. We
compute analytically the 21-cm cross-correlation with the CMB temperature
anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio
for its detection with Planck together with LOFAR, MWA and SKA. We find, on the
one hand, that the 21-cm cross-correlation signal with CMB polarisation from
the instant reionisation can be detected with an SN ratio of for LOFAR
and for SKA. On the other hand, we confirm that the detection of the
21-cm cross-correlation with CMB polarisation is practically infeasible.Comment: 12 figure