Advanced radio interferometric simulation and data reduction techniques

This work shows how legacy and novel radio Interferometry software packages and algorithms can be combined to produce high-quality reductions from modern telescopes, as well as end-to-end simulations for upcoming instruments such as the Square Kilometre Array (SKA) and its pathfinders. We first use a MeqTrees based simulations framework to quantify how artefacts due to direction-dependent effects accumulate with time, and the consequences of this accumulation when observing the same field multiple times in order to reach the survey depth. Our simulations suggest that a survey like LADUMA (Looking at the Distant Universe with MeerKAT Array), which aims to achieve its survey depth of 16 µJy/beam in a 72 kHz at 1.42 GHz by observing the same field for 1000 hours, will be able to reach its target depth in the presence of these artefacts. We also present stimela, a system agnostic scripting framework for simulating, processing and imaging radio interferometric data. This framework is then used to write an end-to-end simulation pipeline in order to quantify the resolution and sensitivity of the SKA1-MID telescope (the first phase of the SKA mid-frequency telescope) as a function of frequency, as well as the scale-dependent sensitivity of the telescope. Finally, a stimela-based reduction pipeline is used to process data of the field around the source 3C147, taken by the Karl G. Jansky Very Large Array (VLA). The reconstructed image from this reduction has a typical 1a noise level of 2.87 µJy/beam, and consequently a dynamic range of 8x106:1, given the 22.58 Jy/beam flux Density of the source 3C147

The effect of the variable chaplygin gas on the CMB.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.In this dissertation, we consider the variable chaplygin gas (VCG) model as derived from the Tachyon gas model and search for a sub-class of models that provide an adequate fit to the cosmic microwave background (CMB) observations. We find that, for an appropriate choice of VCG parameters, up to ~ 80% of the VCG collapses into a gravitationally bound condensate which behaves as matter; the evolution of the remaining VCG, as governed by its equation of state, brings about accelerated expansion at late times. In light of this high collapsed fraction, we approximate the VCG transfer function with that of cold dark matter. We show that we can sufficiently describe the VCG cosmology from decoupling to today in terms of a model in which the gravitationally bound condensate plays the role of cold dark matter and the remaining VCG takes the place of dark energy in the concordance model. We then compute the CMB temperature anisotropy spectrum for a subset of VCG models and proceed to find a best-fit model to the WMAP-9yr data [46]. Our best-fit model has a x² per degrees of freedom of 2.03

RadioLensfit: Bayesian weak lensing measurement in the visibility domain

Observationally, weak lensing has been served so far by optical surveys due to the much larger number densities of background galaxies achieved, which is typically by two to three orders of magnitude compared to radio. However, the high sensitivity of the new generation of radio telescopes such as the Square Kilometre Array (SKA) will provide a density of detected galaxies that is comparable to that found at optical wavelengths, and with significant source shape measurements to make large area radio surveys competitive for weak lensing studies. This will lead weak lensing to become one of the primary science drivers in radio surveys too, with the advantage that they will access the largest scales in the Universe going beyond optical surveys, like LSST and Euclid, in terms of redshifts that are probed. RadioLensfit is an adaptation to radio data of "lensfit", a model-fitting approach for galaxy shear measurement, originally developed for optical weak lensing surveys. Its key advantage is working directly in the visibility domain, which is the natural approach to adopt with radio data, avoiding systematics due to the imaging process. We present results on galaxy shear measurements, including investigation of sensitivity to instrumental parameters such as the visibilities gridding size, based on simulations of individual galaxy visibilities performed by using SKA1-MID baseline configuration. We get an amplitude of the shear bias in the method comparable with SKA1 requirements for a population of galaxies with realistic flux and scalelength distributions estimated from the VLA SWIRE catalog.Comment: 4 pages, 4 figures, The many facets of extragalactic radio surveys: towards new scientific challenges, Bologna 20-23, 201

MeerKAT follow-up of enigmatic GLEAM 4-Jy (G4Jy) sources

We present the results from studying 140 radio sources in the GLEAM (GaLactic and Extragalactic All-sky MWA [Murchison Widefield Array]) 4-Jy (G4Jy) Sample. These sources were followed-up with MeerKAT to assess their radio morphology and enable host-galaxy identification, as existing radio images of 25 to 45-arcsec resolution do not provide sufficient information. We refer to these sources as the MeerKAT-2019 subset. The aim is to identify the host galaxy of these sources by visually inspecting the overlays comprising radio data from four surveys (at 150, 200, 843/1400, and 1300 MHz). Our morphological classification and host-galaxy identification relies upon the ~7-arcsec resolution images from MeerKAT (1300 MHz). Through the visual inspection of the overlays, 14 radio sources in the MeerKAT-2019 subset have wide-angle tail (WAT) morphology, 10 are head-tail, and 5 have X-, S-/Z-shaped morphology. Most of the remaining sources have the radio morphology of typical symmetric lobes. Of 140 sources, we find host galaxies for 98 sources, leaving 42 with no identified host galaxy. These 42 sources still have ambiguous identification even with higher resolution images from MeerKAT.Comment: 20 pages, 16 figures, 4 tables. Accepted in MNRA

A Spectropolarimetric Study of Pictor A Radio Galaxy with MeerKAT

We present the results of a polarimetric study from our new high-sensitivity L-band (0.8--1.7 GHz) observation of Pictor A with the MeerKAT radio telescope. We confirm the presence of the radio jet extending from the nucleus to the western hotspot of this source. Additionally, we show the radio emission expected to be coincident with previously observed X-ray emission in the radio lobes, confirming that the emission mechanism is of inverse Compton origin, as suggested by a previous study. Our spectropolarimetric analysis using the RM-Synthesis technique reveals a relatively uniform mean RM distribution across the lobes of Pictor A, with most lines-of-sight exhibiting single-peaked Faraday spectra. However, a number of the lines-of-sight exhibit single peaked spectra with a wide base or multiple peaks, suggesting the presence of multiple Faraday components or a Faraday thick structure along Pictor A's lines-of-sight. We also confirm the asymmetry in RM variability and depolarization between the two lobes of this source which were reported in a previous study.Comment: 15 pages,15 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review. The version of record [Andati L.A.L. et al., 2024] is available online at: https://doi.org/10.1093/mnras/stae59

A new look at old friends – I. Imaging classical radio galaxies with uGMRT and MeerKAT

We have undertaken a systematic study of FR I and FR II radio galaxies with the upgraded Giant Metrewave Radio Telescope (uGMRT) and MeerKAT. The main goal is to explore whether the unprecedented few μJy sensitivity reached in the range 550–1712 MHz at the resolution of ∼4–7 arcsec reveals new features in the radio emission which might need us to revise our current classification scheme for classical radio galaxies. In this paper, we present the results for the first set of four radio galaxies, i.e. 4C 12.02, 4C 12.03, CGCG 044–046, and CGCG 021–063. The sources have been selected from the 4C sample with well-defined criteria and have been imaged with the uGMRT in the range 550–850 MHz (band 4) and with the MeerKAT in the range 856–1712 MHz (L-band). Full resolution images are presented for all sources in the sample, together with MeerKAT in-band spectral images. Additionally, the uGMRT–MeerKAT spectral image and MeerKAT L-band polarization structure are provided for CGCG 044–046. Our images contain a wealth of morphological details, such as filamentary structure in the emission from the lobes, radio emission beyond the hotspots in three sources, and misalignments. We briefly discuss the overall properties of CGCG 044–046 in the light of the local environment as well, and show possible restarted activity in 4C 12.03 which needs to be confirmed. We conclude that at least for the sources presented here, the classical FR I/FR II morphological classification still holds with the current improved imaging capabilities, but the richness in details also suggests caution in the systematic morphological classification carried out with automatic procedures in surveys with poorer sensitivity and angular resolution.http://mnras.oxfordjournals.orghj2022Physic

Viewing classical radio galaxies with the upgraded GMRT and MeerKAT

We present a progress report of a study of FR I and FR II radio galaxies. Several new morphological features in the radio emission are now revealed using the high (mJy) sensitivity reached in the range 550–1712 MHz, more than a factor of three, at the high ( 400 700) angular resolution with the upgraded Giant Metrewave Radio Telescope (uGMRT) and MeerKAT. Therefore, the aim of this study is to understand if we need to revise our current classification scheme for classical radio galaxies. In order to address our goals, we have carefully constructed a sample of 14 (6 FR I, 6 FR II and 2 FR 0) radio galaxies. The uGMRT and MeerKAT images of our four target sources revealed a wealth of morphological details, e.g., filamentary structure in the emission from the lobes, misalignments, radio emission beyond the hot-spots in three sources, etc.; see Fanaroff et al. (2021). Here, we present preliminary results for two more radio galaxies from our sample using uGMRT, in the light of the local environment. Finally, we are awaiting uGMRT and MeerKAT observations of remaining sample sources. Our results show that for the radio galaxies in this study, the morphological classification scheme for the classical FR I/FR II radio galaxies still holds, even with the improved imaging capabilities of the uGMRT and MeerKAT. Furthermore, we need to be cautious when using automated procedures for classification schemes, e.g., in surveys (with poorer sensitivities and angular resolutions) because of the rich morphological details that are shown in our uGMRT and MeerKAT images.The Department of Atomic Energy, Government of India; the Ministero degli Affari Esteri e della Cooperazione Internazionale, Direzione Generale per la Promozione del Sistema Paese, Progetto di Grande Rilevanza; the South African Research Chairs Initiative of the Department of Science and Technology; the National Research Foundation; the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme; the Italian Minister for Research and Education (MIUR) and the South African Radio Astronomy Observatory.https://www.mdpi.com/journal/galaxiesam2022Physic

MeerKLASS: MeerKAT Large Area Synoptic Survey

We discuss the ground-breaking science that will be possible with a wide area survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area Synoptic Survey). The current specifications of MeerKAT make it a great fit for science applications that require large survey speeds but not necessarily high angular resolutions. In particular, for cosmology, a large survey over $\sim 4,000 \, {\rm deg}^2$ for $\sim 4,000$ hours will potentially provide the first ever measurements of the baryon acoustic oscillations using the 21cm intensity mapping technique, with enough accuracy to impose constraints on the nature of dark energy. The combination with multi-wavelength data will give unique additional information, such as exquisite constraints on primordial non-Gaussianity using the multi-tracer technique, as well as a better handle on foregrounds and systematics. Such a wide survey with MeerKAT is also a great match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era for galaxies resolved in the HI emission line beyond local structures at z > 0.01. It will also produce a large continuum galaxy sample down to a depth of about 5\,$\mu$Jy in L-band, which is quite unique over such large areas and will allow studies of the large-scale structure of the Universe out to high redshifts, complementing the galaxy HI survey to form a transformational multi-wavelength approach to study galaxy dynamics and evolution. Finally, the same survey will supply unique information for a range of other science applications, including a large statistical investigation of galaxy clusters as well as produce a rotation measure map across a huge swathe of the sky. The MeerKLASS survey will be a crucial step on the road to using SKA1-MID for cosmological applications and other commensal surveys, as described in the top priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201