7 research outputs found
Scalable precision wide-field imaging in radio interferometry: I. uSARA validated on ASKAP data
As Part I of a paper series showcasing a new imaging framework, we consider
the recently proposed unconstrained Sparsity Averaging Reweighted Analysis
(uSARA) optimisation algorithm for wide-field, high-resolution, high-dynamic
range, monochromatic intensity imaging. We reconstruct images from real
radio-interferometric observations obtained with the Australian Square
Kilometre Array Pathfinder (ASKAP) and present these results in comparison to
the widely-used, state-of-the-art imager WSClean. Selected fields come from the
ASKAP Early Science and Evolutionary Map of the Universe (EMU) Pilot surveys
and contain several complex radio sources: the merging cluster system Abell
3391-95, the merging cluster SPT-CL 2023-5535, and many extended, or bent-tail,
radio galaxies, including the X-shaped radio galaxy PKS 2014-558 and the
``dancing ghosts'', known collectively as PKS 2130-538. The modern framework
behind uSARA utilises parallelisation and automation to solve for the w-effect
and efficiently compute the measurement operator, allowing for wide-field
reconstruction over the full field-of-view of individual ASKAP beams (up to 3.3
deg each). The precision capability of uSARA produces images with both
super-resolution and enhanced sensitivity to diffuse components, surpassing
traditional CLEAN algorithms which typically require a compromise between such
yields. Our resulting monochromatic uSARA-ASKAP images of the selected data
highlight both extended, diffuse emission and compact, filamentary emission at
very high resolution (up to 2.2 arcsec), revealing never-before-seen structure.
Here we present a validation of our uSARA-ASKAP images by comparing the
morphology of reconstructed sources, measurements of diffuse flux, and spectral
index maps with those obtained from images made with WSClean.Comment: Accepted for publication in MNRA
Scalable precision wide-field imaging in radio interferometry: II. AIRI validated on ASKAP data
Accompanying Part I, this sequel delineates a validation of the recently
proposed AI for Regularisation in radio-interferometric Imaging (AIRI)
algorithm on observations from the Australian Square Kilometre Array Pathfinder
(ASKAP). The monochromatic AIRI-ASKAP images showcased in this work are formed
using the same parallelised and automated imaging framework described in Part
I: ``uSARA validated on ASKAP data''. Using a Plug-and-Play approach, AIRI
differs from uSARA by substituting a trained denoising deep neural network
(DNN) for the proximal operator in the regularisation step of the
forward-backward algorithm during deconvolution. We build a trained shelf of
DNN denoisers which target the estimated image-dynamic-ranges of our selected
data. Furthermore, we quantify variations of AIRI reconstructions when
selecting the nearest DNN on the shelf versus using a universal DNN with the
highest dynamic range, opening the door to a more complete framework that not
only delivers image estimation but also quantifies epistemic model uncertainty.
We continue our comparative analysis of source structure, diffuse flux
measurements, and spectral index maps of selected target sources as imaged by
AIRI and the algorithms in Part I -- uSARA and WSClean. Overall we see an
improvement over uSARA and WSClean in the reconstruction of diffuse components
in AIRI images. The scientific potential delivered by AIRI is evident in
further imaging precision, more accurate spectral index maps, and a significant
acceleration in deconvolution time, whereby AIRI is four times faster than its
sub-iterative sparsity-based counterpart uSARA.Comment: Accepted for publication in MNRA
Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395
The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is similar to 50 ' or similar to 3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of (1 GHz) (1GHz)0.7 Mpc is approximate to 1.7 deg(-2), three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos