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
Studying the brightest radio sources in the southern sky
- Authors: Sejake, Precious Katlego
- Date: 2022-04-06
- Subjects: Galaxies Formation , Galaxies Evolution , Active galaxies , Radio galaxies , Radio sources (Astronomy) , Southern sky (Astronomy)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455350 , vital:75423
- Description: Active Galactic Nuclei (AGN) are among the most remarkable and powerful extragalactic radio sources in the Universe. The study of AGN enables us to understand better the critical mechanisms leading to the launch of radio jets, and its link to the central engine. Radio jets are thought to impact their host galaxy by promoting or suppressing star formation. By studying AGN, we can better understand their formation, evolution, and environment. The host galaxy cross-identification is a crucial step to be carried out to build a multi-wavelength analysis of powerful radio sources; AGN. The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) 4Jy (G4Jy) Sample comprises 1,863 of the powerful radio sources in the southern sky. However, 140 sources from the G4Jy Sample were followed-up with the Open Time on MeerKAT. Of these 140 sources, 126 had an ambiguous host galaxy, and 13 had an identified host galaxy; however, there were some discrepancies in the literature concerning the host galaxy. The host-galaxy identification of these sources is limited by the poor resolution of radio data at 25" to 45". This study aims to assess the radio morphology of these 140 sources and identify their host galaxy using the ⇠ 7” resolution images from MeerKAT in conjunction with datasets at other wavelengths. This analysis is carried out by visually inspecting the overlays. The overlays comprise radio contours from 150 MHz, 200 MHz, 843/1400 MHz and 1300 MHz overlaid on the mid-infrared image (3.4 μm). The MeerKAT images reveal sources with various radio morphologies. While most of the sources have radio morphology of typical symmetric lobes, 10 radio sources have head-tail morphology, 14 are wide-angle tail (WAT), and 5 have X-, S- /Z-shaped morphology. Overall, we find host galaxies for 70% of the sources in the sample, with the remainder comprising sources with ambiguous host galaxy (20.7%) and sources with a faint mid-infrared host galaxy (9.3%). These results highlight the importance of angular resolution and sensitivity for morphological classification and host galaxy cross-identification. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Sejake, Precious Katlego
- Date: 2022-04-06
- Subjects: Galaxies Formation , Galaxies Evolution , Active galaxies , Radio galaxies , Radio sources (Astronomy) , Southern sky (Astronomy)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455350 , vital:75423
- Description: Active Galactic Nuclei (AGN) are among the most remarkable and powerful extragalactic radio sources in the Universe. The study of AGN enables us to understand better the critical mechanisms leading to the launch of radio jets, and its link to the central engine. Radio jets are thought to impact their host galaxy by promoting or suppressing star formation. By studying AGN, we can better understand their formation, evolution, and environment. The host galaxy cross-identification is a crucial step to be carried out to build a multi-wavelength analysis of powerful radio sources; AGN. The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) 4Jy (G4Jy) Sample comprises 1,863 of the powerful radio sources in the southern sky. However, 140 sources from the G4Jy Sample were followed-up with the Open Time on MeerKAT. Of these 140 sources, 126 had an ambiguous host galaxy, and 13 had an identified host galaxy; however, there were some discrepancies in the literature concerning the host galaxy. The host-galaxy identification of these sources is limited by the poor resolution of radio data at 25" to 45". This study aims to assess the radio morphology of these 140 sources and identify their host galaxy using the ⇠ 7” resolution images from MeerKAT in conjunction with datasets at other wavelengths. This analysis is carried out by visually inspecting the overlays. The overlays comprise radio contours from 150 MHz, 200 MHz, 843/1400 MHz and 1300 MHz overlaid on the mid-infrared image (3.4 μm). The MeerKAT images reveal sources with various radio morphologies. While most of the sources have radio morphology of typical symmetric lobes, 10 radio sources have head-tail morphology, 14 are wide-angle tail (WAT), and 5 have X-, S- /Z-shaped morphology. Overall, we find host galaxies for 70% of the sources in the sample, with the remainder comprising sources with ambiguous host galaxy (20.7%) and sources with a faint mid-infrared host galaxy (9.3%). These results highlight the importance of angular resolution and sensitivity for morphological classification and host galaxy cross-identification. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Date Issued: 2022-04-06
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