New insights on classical radio galaxies from MeerKAT and uGMRT
- Authors: Legodi, Portia Potasi
- Date: 2025-04-03
- Subjects: Radio galaxies , MeerKAT , Giant Metrewave Radio Telescope , Radio sources (Astronomy) , Radio interferometers
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/479886 , vital:78376 , DOI 10.21504/10962/479886
- Description: The morphology of low and high-power sources has been the subject of a classification method for over four decades, leading to a comprehensive understanding of extragalactic radio sources. The morphological classification of radio galaxies is again a hot topic. This project aims to revisit the current classification scheme for classical radio galaxies and investigate the properties and origin of the new filamentary features which are becoming standard within and outside the radio lobes and which are suggestive of so far unexplored interactions between the radio plasma and the external medium. This thesis presents high-resolution and sensitivity studies of the nature of ten known radio galaxies: three FRIs (4C -03.43, 3C 403.1, 3C 198), three FRIIs (3C 105, 3C 227, 3C 445), tailed radio sources (CGCG046-067, NGC7503) and the FR0s (SDSS J 09157+1331, SDSS J 1120+0407). The total sample was selected from the 4C catalogue with well-defined criteria. To this aim, we are using the μJy sensitivity offered by the combination of uGMRT and MeerKAT in a frequency range from 500−1712 MHz. The radio images present several new morphological features in the radio emission at a ∼4′′ −10′′ angular resolution. Our radio maps validate the morphological classification. The sources exhibit remarkable features that raise new questions regarding the complex interaction between radio plasma emitted by host galaxies and the surrounding medium through which the jet propagates. The wealth of morphological details includes, for example, the detection of filaments in the emission from the lobes, the existence of diffuse emission beyond the hotspots, and multiple knot-like structures along the jet spine in some sources in the sample. Detailed descriptions of the overall radio structures are presented. We derived the equipartition parameters for each source in the sample, and after fitting their integrated spectrum, we estimated their global radiative ages. We find a broad range of radiative ages, i.e. 40.19−242.85 Myr. We derived in-band spectral index imaging for a few radio galaxies in the sample. This allowed us to make some preliminary considerations on the origin of the various radio features. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2025
- Full Text:
- Date Issued: 2025-04-03
- Authors: Legodi, Portia Potasi
- Date: 2025-04-03
- Subjects: Radio galaxies , MeerKAT , Giant Metrewave Radio Telescope , Radio sources (Astronomy) , Radio interferometers
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/479886 , vital:78376 , DOI 10.21504/10962/479886
- Description: The morphology of low and high-power sources has been the subject of a classification method for over four decades, leading to a comprehensive understanding of extragalactic radio sources. The morphological classification of radio galaxies is again a hot topic. This project aims to revisit the current classification scheme for classical radio galaxies and investigate the properties and origin of the new filamentary features which are becoming standard within and outside the radio lobes and which are suggestive of so far unexplored interactions between the radio plasma and the external medium. This thesis presents high-resolution and sensitivity studies of the nature of ten known radio galaxies: three FRIs (4C -03.43, 3C 403.1, 3C 198), three FRIIs (3C 105, 3C 227, 3C 445), tailed radio sources (CGCG046-067, NGC7503) and the FR0s (SDSS J 09157+1331, SDSS J 1120+0407). The total sample was selected from the 4C catalogue with well-defined criteria. To this aim, we are using the μJy sensitivity offered by the combination of uGMRT and MeerKAT in a frequency range from 500−1712 MHz. The radio images present several new morphological features in the radio emission at a ∼4′′ −10′′ angular resolution. Our radio maps validate the morphological classification. The sources exhibit remarkable features that raise new questions regarding the complex interaction between radio plasma emitted by host galaxies and the surrounding medium through which the jet propagates. The wealth of morphological details includes, for example, the detection of filaments in the emission from the lobes, the existence of diffuse emission beyond the hotspots, and multiple knot-like structures along the jet spine in some sources in the sample. Detailed descriptions of the overall radio structures are presented. We derived the equipartition parameters for each source in the sample, and after fitting their integrated spectrum, we estimated their global radiative ages. We find a broad range of radiative ages, i.e. 40.19−242.85 Myr. We derived in-band spectral index imaging for a few radio galaxies in the sample. This allowed us to make some preliminary considerations on the origin of the various radio features. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2025
- Full Text:
- Date Issued: 2025-04-03
KalCal: a novel calibration framework for radio interferometry using the Kalman Filter and Smoother
- Authors: Welman, Brian Allister
- Date: 2024-10-11
- Subjects: Radio interferometers , Calibration , Kalman filtering , Bayesian inference , Signal processing , Radio astronomy , MeerKAT
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/467127 , vital:76818
- Description: Calibration in radio interferometry is essential for correcting measurement errors. Traditional methods employ maximum likelihood techniques and non-linear least squares solvers but face challenges due to the data volumes and increased noise sensitivity of contemporary instruments such as MeerKAT. A common approach for mitigating these issues is using “solution intervals”, which helps manage the data volume and reduces overfitting. However, inappropriate interval sizes can degrade calibration quality, and determining optimal sizes is challenging, often relying on brute-force methods. This study introduces Kalman Filtering and Smoothing in Calibration (KalCal), a new framework for calibration that combines the Kalman Filter, Kalman Smoother, and the energy function: the negative logarithm of the Bayesian evidence. KalCal offers Bayesian-optimal solutions as probability densities and models calibration effects with lower computational requirements than iterative approaches. Unlike traditional methods, which require all the data for a particular solution to be in memory simultaneously, KalCal’s recursive computations only need a single pass through the data with appropriate prior information. The energy function provides the means for KalCal to determine this prior information. Theoretical contributions include additions to complex optimisation literature and the “Kalman-Woodbury Identity” that reformulates the traditional Kalman Filter. A Python implementation of the KalCal framework was benchmarked against solution intervals as implemented in the QuartiCal package. Simulations show KalCal matching solution intervals in high Signal-to-Noise Ratio (SNR) scenarios and surpassing them in low SNR conditions. Moreover, the energy function produced minima that coincide with KalCal’s Mean Square Error (MSE) on the true gain signal. This result is significant as the MSE is unavailable in real applications. Further research is needed to assess the computational feasibility and intricacies of KalCal. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Welman, Brian Allister
- Date: 2024-10-11
- Subjects: Radio interferometers , Calibration , Kalman filtering , Bayesian inference , Signal processing , Radio astronomy , MeerKAT
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/467127 , vital:76818
- Description: Calibration in radio interferometry is essential for correcting measurement errors. Traditional methods employ maximum likelihood techniques and non-linear least squares solvers but face challenges due to the data volumes and increased noise sensitivity of contemporary instruments such as MeerKAT. A common approach for mitigating these issues is using “solution intervals”, which helps manage the data volume and reduces overfitting. However, inappropriate interval sizes can degrade calibration quality, and determining optimal sizes is challenging, often relying on brute-force methods. This study introduces Kalman Filtering and Smoothing in Calibration (KalCal), a new framework for calibration that combines the Kalman Filter, Kalman Smoother, and the energy function: the negative logarithm of the Bayesian evidence. KalCal offers Bayesian-optimal solutions as probability densities and models calibration effects with lower computational requirements than iterative approaches. Unlike traditional methods, which require all the data for a particular solution to be in memory simultaneously, KalCal’s recursive computations only need a single pass through the data with appropriate prior information. The energy function provides the means for KalCal to determine this prior information. Theoretical contributions include additions to complex optimisation literature and the “Kalman-Woodbury Identity” that reformulates the traditional Kalman Filter. A Python implementation of the KalCal framework was benchmarked against solution intervals as implemented in the QuartiCal package. Simulations show KalCal matching solution intervals in high Signal-to-Noise Ratio (SNR) scenarios and surpassing them in low SNR conditions. Moreover, the energy function produced minima that coincide with KalCal’s Mean Square Error (MSE) on the true gain signal. This result is significant as the MSE is unavailable in real applications. Further research is needed to assess the computational feasibility and intricacies of KalCal. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
SolarKAT: a solar imaging pipeline for MeerKAT
- Samboco, Victória da Graça Gilberto
- Authors: Samboco, Victória da Graça Gilberto
- Date: 2024-10-11
- Subjects: MeerKAT , Radio interferometers , Solar activity , Radio Interference , Data processing
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465102 , vital:76573
- Description: Solar interference poses a significant challenge in radio interferometric observations, particularly with the increasing sensitivity of modern new-generation telescopes. This thesis presents the SolarKAT pipeline, a novel approach designed to mitigate solar interference in MeerKAT observations. The pipeline incorporates a series of steps, including self-calibration (second generation calibration or 2GC), precise determination of the Sun’s position, phase centre adjustments, creation of region-based masks, deconvolution, prediction, solar model subtraction, and peeling. We applied the SolarKAT pipeline to three datasets that feature the Sun in different conditions (frequency band and angular distance from the Sun to the telescope pointing position). These observations were obtained from three MeerKAT telescope surveys: ThunderKAT, MIGHTEE and LADUMA. We compared the visual images, peak fluxes, flux density, RMS and pixel distribution to evaluate the pipeline. Our results showed a notable reduction in solar interference. This is evidenced by the improved image quality, reduction in RMS and pixel distribution values, and consistent peak flux measurements after applying the pipeline. SolarKAT has not only improved the data quality but also demonstrated to be a valuable tool in producing high-quality solar images, which can be a helpful resource for solar physics and space weather forecasts. This study showcases the potential of the SolarKAT pipeline in enabling high-quality radio interferometric observations, even in the presence of solar interference. Unlike conventional methods that often discard corrupted visibilities (e.g. flagging), our approach focuses on recovering them. Additionally, the SolarKAT pipeline naturally delivers detailed images of the Sun. Our findings contribute to advancing the field of radio interferometry, providing a valuable tool for researchers seeking to enhance the accuracy of their observations and conduct studies in solar physics and space weather. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Samboco, Victória da Graça Gilberto
- Date: 2024-10-11
- Subjects: MeerKAT , Radio interferometers , Solar activity , Radio Interference , Data processing
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/465102 , vital:76573
- Description: Solar interference poses a significant challenge in radio interferometric observations, particularly with the increasing sensitivity of modern new-generation telescopes. This thesis presents the SolarKAT pipeline, a novel approach designed to mitigate solar interference in MeerKAT observations. The pipeline incorporates a series of steps, including self-calibration (second generation calibration or 2GC), precise determination of the Sun’s position, phase centre adjustments, creation of region-based masks, deconvolution, prediction, solar model subtraction, and peeling. We applied the SolarKAT pipeline to three datasets that feature the Sun in different conditions (frequency band and angular distance from the Sun to the telescope pointing position). These observations were obtained from three MeerKAT telescope surveys: ThunderKAT, MIGHTEE and LADUMA. We compared the visual images, peak fluxes, flux density, RMS and pixel distribution to evaluate the pipeline. Our results showed a notable reduction in solar interference. This is evidenced by the improved image quality, reduction in RMS and pixel distribution values, and consistent peak flux measurements after applying the pipeline. SolarKAT has not only improved the data quality but also demonstrated to be a valuable tool in producing high-quality solar images, which can be a helpful resource for solar physics and space weather forecasts. This study showcases the potential of the SolarKAT pipeline in enabling high-quality radio interferometric observations, even in the presence of solar interference. Unlike conventional methods that often discard corrupted visibilities (e.g. flagging), our approach focuses on recovering them. Additionally, the SolarKAT pipeline naturally delivers detailed images of the Sun. Our findings contribute to advancing the field of radio interferometry, providing a valuable tool for researchers seeking to enhance the accuracy of their observations and conduct studies in solar physics and space weather. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-10-11
MeerKAT observations of the Abell 141 galaxy cluster
- Authors: Stanbury, Savannah Mae
- Date: 2024-04-04
- Subjects: MeerKAT , Radio astronomy , Radio interferometers , Galaxies Clusters , Electromagnetic waves
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435378 , vital:73152
- Description: This study is aimed at being an overview and investigation of the behaviour and morphology of radio quiet (RQ) active galactic nuclei (AGN) in the radio and optical/near-infrared (NIR) bands. It is hoped that a concise description of the relation that exists between accretion activity and star formation (SF) will be achieved through utilization of multiwavelength astronomy analysis. This analysis includes the processing of data acquired from the MeerKAT International GHz Tiered Extragalactic Exploration survey (MIGHTEE), the Southern African Large Telescope (SALT), the Hyper Suprime Camera (HSC) mounted on the Subaru telescope and the VISTA telescope. In this thesis, several targets were observed using SALT spectroscopy, but a redshift of only one of them was obtained. Lastly, it was established that for the sample of RQ AGN studied, the AGN contribute a large fraction of the radio emission observed. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-04-04
- Authors: Stanbury, Savannah Mae
- Date: 2024-04-04
- Subjects: MeerKAT , Radio astronomy , Radio interferometers , Galaxies Clusters , Electromagnetic waves
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435378 , vital:73152
- Description: This study is aimed at being an overview and investigation of the behaviour and morphology of radio quiet (RQ) active galactic nuclei (AGN) in the radio and optical/near-infrared (NIR) bands. It is hoped that a concise description of the relation that exists between accretion activity and star formation (SF) will be achieved through utilization of multiwavelength astronomy analysis. This analysis includes the processing of data acquired from the MeerKAT International GHz Tiered Extragalactic Exploration survey (MIGHTEE), the Southern African Large Telescope (SALT), the Hyper Suprime Camera (HSC) mounted on the Subaru telescope and the VISTA telescope. In this thesis, several targets were observed using SALT spectroscopy, but a redshift of only one of them was obtained. Lastly, it was established that for the sample of RQ AGN studied, the AGN contribute a large fraction of the radio emission observed. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2024
- Full Text:
- Date Issued: 2024-04-04
MeerKAT observations of three high-redshift galaxy clusters
- Authors: Manaka, Sinah Mokatako
- Date: 2023-03-29
- Subjects: MeerKAT , Galaxies Clusters , Calibration , Radio interferometers , Radio halo
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422367 , vital:71936
- Description: Galaxy clusters are the largest, gravitationally-bound structures in the Universe, formed through the hierarchical merger of smaller structures. The most accepted view is that the merging process injects energy into the intracluster medium (ICM) and re-accelerates pre-existing particles and compresses magnetic fields, generating, eventually, synchrotron emission. Such radio emission appears as radio halos, i.e. central Mpc-size diffuse structures, mostly visible in merging or unrelaxed clusters and with a spatial correspondence with the thermal gas component of the ICM. Observations have probed radio halo properties mostly for clusters withM500 > 6×1014 M⊙ at intermediate redshifts (0.3 < z < 0.4), providing support to their connection between mergers, which provide the necessary energy to re-accelerate particles via turbulence. Probing the redshift evolution of radio halos is an important test of the turbulent re-acceleration scenario, as fewer halos are expected at high redshift, given the same mass interval. In this thesis, we present MeerKAT observations at 1.28 GHz of three high-redshift (PSZ2G254.08- 58.45, PSZ2G255.60-46.18 and PSZ2G277.76-51.74, in the 0.42 ≲ z ≲ 0.46 range) clusters, with masses M500 ≳ 6.2 × 1014 M⊙, selected for their disturbed dynamical state – inferred from existing X-ray observations. Our observations reached rms noise values between 20 and 23.5 μJy beam−1, with ∼ 4′′ angular resolution. No evidence of diffuse emission is found at ii full resolution. Low-resolution (∼ 30′′) images achieved rms noise levels of 30-50 μJy beam−1, amongst the deepest observations of high-redshift targets. One radio halo was detected in the least massive cluster PSZ2G254.08-58.45 extending over ∼ 500 kpc, with a 1.20 } 0.08 mJy integrated flux density. We placed a ∼1 mJy upper limit at 95% confidence level on the radio halo flux density for the other two targets. The radio-halo detection is consistent with the recent P1.4 GHz − M500 correlation from Cuciti et al. (2021b), while the upper limit on PSZ2G255.60-46.18 is consistent with being on the correlation. On the other hand, the upper limit on PSZ2G277.76-51.74 places the radio halo well below the correlation. Recently a 1.5 GHz survey (Giovannini et al., 2020) detected a slightly higher fraction of radio halos in clusters in the same redshift range, with power and size typically higher than what we found in our observations. Both observations are, however, not inconsistent with each other. Our results, although with limited statistics, do not disfavour the current scenario of radiohalo formation based on the turbulent re-acceleration model. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Manaka, Sinah Mokatako
- Date: 2023-03-29
- Subjects: MeerKAT , Galaxies Clusters , Calibration , Radio interferometers , Radio halo
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422367 , vital:71936
- Description: Galaxy clusters are the largest, gravitationally-bound structures in the Universe, formed through the hierarchical merger of smaller structures. The most accepted view is that the merging process injects energy into the intracluster medium (ICM) and re-accelerates pre-existing particles and compresses magnetic fields, generating, eventually, synchrotron emission. Such radio emission appears as radio halos, i.e. central Mpc-size diffuse structures, mostly visible in merging or unrelaxed clusters and with a spatial correspondence with the thermal gas component of the ICM. Observations have probed radio halo properties mostly for clusters withM500 > 6×1014 M⊙ at intermediate redshifts (0.3 < z < 0.4), providing support to their connection between mergers, which provide the necessary energy to re-accelerate particles via turbulence. Probing the redshift evolution of radio halos is an important test of the turbulent re-acceleration scenario, as fewer halos are expected at high redshift, given the same mass interval. In this thesis, we present MeerKAT observations at 1.28 GHz of three high-redshift (PSZ2G254.08- 58.45, PSZ2G255.60-46.18 and PSZ2G277.76-51.74, in the 0.42 ≲ z ≲ 0.46 range) clusters, with masses M500 ≳ 6.2 × 1014 M⊙, selected for their disturbed dynamical state – inferred from existing X-ray observations. Our observations reached rms noise values between 20 and 23.5 μJy beam−1, with ∼ 4′′ angular resolution. No evidence of diffuse emission is found at ii full resolution. Low-resolution (∼ 30′′) images achieved rms noise levels of 30-50 μJy beam−1, amongst the deepest observations of high-redshift targets. One radio halo was detected in the least massive cluster PSZ2G254.08-58.45 extending over ∼ 500 kpc, with a 1.20 } 0.08 mJy integrated flux density. We placed a ∼1 mJy upper limit at 95% confidence level on the radio halo flux density for the other two targets. The radio-halo detection is consistent with the recent P1.4 GHz − M500 correlation from Cuciti et al. (2021b), while the upper limit on PSZ2G255.60-46.18 is consistent with being on the correlation. On the other hand, the upper limit on PSZ2G277.76-51.74 places the radio halo well below the correlation. Recently a 1.5 GHz survey (Giovannini et al., 2020) detected a slightly higher fraction of radio halos in clusters in the same redshift range, with power and size typically higher than what we found in our observations. Both observations are, however, not inconsistent with each other. Our results, although with limited statistics, do not disfavour the current scenario of radiohalo formation based on the turbulent re-acceleration model. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2023
- Full Text:
- Date Issued: 2023-03-29
Finite precision arithmetic in Polyphase Filterbank implementations
- Authors: Myburgh, Talon
- Date: 2020
- Subjects: Radio interferometers , Interferometry , Radio telescopes , Gate array circuits , Floating-point arithmetic , Python (Computer program language) , Polyphase Filterbank , Finite precision arithmetic , MeerKAT
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146187 , vital:38503
- Description: The MeerKAT is the most sensitive radio telescope in its class, and it is important that systematic effects do not limit the dynamic range of the instrument, preventing this sensitivity from being harnessed for deep integrations. During commissioning, spurious artefacts were noted in the MeerKAT passband and the root cause was attributed to systematic errors in the digital signal path. Finite precision arithmetic used by the Polyphase Filterbank (PFB) was one of the main factors contributing to the spurious responses, together with bugs in the firmware. This thesis describes a software PFB simulator that was built to mimic the MeerKAT PFB and allow investigation into the origin and mitigation of the effects seen on the telescope. This simulator was used to investigate the effects in signal integrity of various rounding techniques, overflow strategies and dual polarisation processing in the PFB. Using the simulator to investigate a number of different signal levels, bit-width and algorithmic scenarios, it gave insight into how the periodic dips occurring in the MeerKAT passband were the result of the implementation using an inappropriate rounding strategy. It further indicated how to select the best strategy for preventing overflow while maintaining high quantization effciency in the FFT. This practice of simulating the design behaviour in the PFB independently of the tools used to design the DSP firmware, is a step towards an end-to-end simulation of the MeerKAT system (or any radio telescope using nite precision digital signal processing systems). This would be useful for design, diagnostics, signal analysis and prototyping of the overall instrument.
- Full Text:
- Date Issued: 2020
- Authors: Myburgh, Talon
- Date: 2020
- Subjects: Radio interferometers , Interferometry , Radio telescopes , Gate array circuits , Floating-point arithmetic , Python (Computer program language) , Polyphase Filterbank , Finite precision arithmetic , MeerKAT
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146187 , vital:38503
- Description: The MeerKAT is the most sensitive radio telescope in its class, and it is important that systematic effects do not limit the dynamic range of the instrument, preventing this sensitivity from being harnessed for deep integrations. During commissioning, spurious artefacts were noted in the MeerKAT passband and the root cause was attributed to systematic errors in the digital signal path. Finite precision arithmetic used by the Polyphase Filterbank (PFB) was one of the main factors contributing to the spurious responses, together with bugs in the firmware. This thesis describes a software PFB simulator that was built to mimic the MeerKAT PFB and allow investigation into the origin and mitigation of the effects seen on the telescope. This simulator was used to investigate the effects in signal integrity of various rounding techniques, overflow strategies and dual polarisation processing in the PFB. Using the simulator to investigate a number of different signal levels, bit-width and algorithmic scenarios, it gave insight into how the periodic dips occurring in the MeerKAT passband were the result of the implementation using an inappropriate rounding strategy. It further indicated how to select the best strategy for preventing overflow while maintaining high quantization effciency in the FFT. This practice of simulating the design behaviour in the PFB independently of the tools used to design the DSP firmware, is a step towards an end-to-end simulation of the MeerKAT system (or any radio telescope using nite precision digital signal processing systems). This would be useful for design, diagnostics, signal analysis and prototyping of the overall instrument.
- Full Text:
- Date Issued: 2020
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