LOFAR sparse image reconstruction

The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components of the sky brightness. Recovering the original brightness distribution with aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods Aims. Recent papers have established a clear link between the discrete nature of radio interferometry measurement and the "compressed sensing" (CS) theory, which supports sparse reconstruction methods to form an image from the measured visibilities. Empowered by proximal theory, CS offers a sound framework for efficient global minimization and sparse data representation using fast algorithms. Combined with instrumental direction-dependent effects (DDE) in the scope of a real instrument, we developed and validated a new method based on this framework Methods. We implemented a sparse reconstruction method in the standard LOFAR imaging tool and compared the photometric and resolution performance of this new imager with that of CLEAN-based methods (CLEAN and MS-CLEAN) with simulated and real LOFAR data Results. We show that i) sparse reconstruction performs as well as CLEAN in recovering the flux of point sources; ii) performs much better on extended objects (the root mean square error is reduced by a factor of up to 10); and iii) provides a solution with an effective angular resolution 2-3 times better than the CLEAN images. Conclusions. Sparse recovery gives a correct photometry on high dynamic and wide-field images and improved realistic structures of extended sources (of simulated and real LOFAR datasets). This sparse reconstruction method is compatible with modern interferometric imagers that handle DDE corrections (A- and W-projections) required for current and future instruments such as LOFAR and SK

Radio imaging of gravitationally lensed radio-quiet quasars

DATA AVAILABILITY : VLA data gathered for this project are publicly available on the VLA archive, which may be accessed at https://data.nrao.edu/ portal under project numbers 20B-309 (PI Jackson) and 23A-278 (PI Jackson).Please read abstract in the article.The Netherlands Organization for Scientific Research (NWO); the Chinese Academy of Sciences (CAS) and in part by the National Research Foundation of South Africa.https://academic.oup.com/mnrashj2024PhysicsNon

Complex angular structure of three elliptical galaxies from high-resolution ALMA observations of strong gravitational lenses

The large-scale mass distributions of galaxy-scale strong lenses have long been assumed to be well described by a singular ellipsoidal power-law density profile with external shear. However, the inflexibility of this model could lead to systematic errors in astrophysical parameters inferred with gravitational lensing observables. Here, we present observations with the Atacama Large (sub-)Millimetre Array (ALMA) of three strongly lensed dusty star-forming galaxies at '30 mas angular resolution and investigate the sensitivity of these data to angular structure in the lensing galaxies. We jointly infer the lensing mass distribution and the full surface brightness of the lensed sources with multipole expansions of the power-law density profile up to the fourth order using a technique developed for interferometric data. All three datasets strongly favour third and fourth-order multipole amplitudes of ≈1 percent of the convergence. While the infrared stellar isophotes and isodensity shapes agree for one lens system, for the other two the isophotes disagree to varying extents, suggesting contributions to the angular structure from dark matter intrinsic or extrinsic to the lensing galaxy.http://www.hanspub.org/Journal/AAS.htmlPhysicsNon

Red quasars blow out molecular gas from galaxies during the peak of cosmic star formation

Galaxie

Gravitational lensing in LoTSS DR2: extremely faint 144-MHz radio emission from two highly magnified quasars

Galaxie

Strong gravitational lensing as a probe of dark matter

Dark matter structures within strong gravitational lens galaxies and along their lines of sight leave a gravitational imprint on the multiple images of lensed sources. Strong gravitational lensing provides, therefore, a key test of different dark matter models. In this article, we describe how galaxy-scale strong gravitational lensing observations are sensitive to the physical nature of dark matter. We provide an historical perspective of the field, and review its current status. We discuss the challenges and advances in terms of data, treatment of systematic errors and theoretical predictions, that will enable one to deliver a stringent and robust test of different dark matter models in the next decade. With the advent of the next generation of sky surveys, the number of known strong gravitational lens systems is expected to increase by several orders of magnitude. Coupled with high-resolution follow-up observations, these data will provide a key opportunity to constrain the properties of dark matter with strong gravitational lensing.The Max Planck Society for support through a Max Planck Lise Meitner Group and funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme; the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodovska-Curie grant agreement No 897124; a Gliese Fellowship; the National Science Foundation; a HQP grant from the McDonald Institute; the Schmidt Futures Foundation; the National Sciences and Engineering Council of Canada; the Fonds de recherche du Québec; the Canada Research Chairs Program; the Netherlands Organization for Scientific Research; the Chinese Academy of Sciences and the National Research Foundation of South Africa. Open Access funding enabled and organized by Projekt DEAL.http://link.springer.com/journal/11214hj2024PhysicsNon