A 150 MHz all sky survey with the Precision Array to Probe the Epoch of Reionization
- Authors: Chege, James Kariuki
- Date: 2020
- Subjects: Epoch of reionization -- Research , Astronomy -- Observations , Radio interferometers
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/117733 , vital:34556
- Description: The Precision Array to Probe the Epoch of Reionization (PAPER) was built to measure the redshifted 21 cm line of hydrogen from cosmic reionization. Such low frequency observations promise to be the best means of understanding the cosmic dawn; when the first galaxies in the universe formed, and also the Epoch of Reionization; when the intergalactic medium changed from neutral to ionized. The major challenges to these observations is the presence of astrophysical foregrounds that are much brighter than the cosmological signal. Here, I present an all-sky survey at 150 MHz obtained from the analysis of 300 hours of PAPER observations. Particular focus is given to the calibration and imaging techniques that need to deal with the wide field of view of a non-tracking instrument. The survey covers ~ 7000 square degrees of the southern sky. From a sky area of 4400 square degrees out of the total survey area, I extract a catalogue of sources brighter than 4 Jy whose accuracy was tested against the published GLEAM catalogue, leading to a fractional difference rms better than 20%. The catalogue provides an all-sky accurate model of the extragalactic foreground to be used for the calibration of future Epoch of Reionization observations and to be subtracted from the PAPER observations themselves in order to mitigate the foreground contamination.
- Full Text:
- Authors: Chege, James Kariuki
- Date: 2020
- Subjects: Epoch of reionization -- Research , Astronomy -- Observations , Radio interferometers
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/117733 , vital:34556
- Description: The Precision Array to Probe the Epoch of Reionization (PAPER) was built to measure the redshifted 21 cm line of hydrogen from cosmic reionization. Such low frequency observations promise to be the best means of understanding the cosmic dawn; when the first galaxies in the universe formed, and also the Epoch of Reionization; when the intergalactic medium changed from neutral to ionized. The major challenges to these observations is the presence of astrophysical foregrounds that are much brighter than the cosmological signal. Here, I present an all-sky survey at 150 MHz obtained from the analysis of 300 hours of PAPER observations. Particular focus is given to the calibration and imaging techniques that need to deal with the wide field of view of a non-tracking instrument. The survey covers ~ 7000 square degrees of the southern sky. From a sky area of 4400 square degrees out of the total survey area, I extract a catalogue of sources brighter than 4 Jy whose accuracy was tested against the published GLEAM catalogue, leading to a fractional difference rms better than 20%. The catalogue provides an all-sky accurate model of the extragalactic foreground to be used for the calibration of future Epoch of Reionization observations and to be subtracted from the PAPER observations themselves in order to mitigate the foreground contamination.
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Observations of diffuse radio emission in the Abell 773 galaxy cluster
- Authors: Sichone, Gift L
- Date: 2020
- Subjects: Galaxies -- Clusters -- Observations , Radio astronomy -- Observations , Astrophysics -- South Africa , Westerbork Radio Telescope , A773 galaxy cluster , Astronomy -- Observations , Radio sources (Astronomy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144945 , vital:38394
- Description: In this thesis, we present 18 and 21 cm observations of the A773 galaxy cluster observed with the Westerbork radio telescope. The final 18 and 21 cm images achieve a noise level of 0.018 mJy beam‾ 1 and 0.025 mJy beam-1 respectively. After subtracting the compact sources, the low resolution images show evidence of a radio halo at 18 cm, whereas its presence is more uncertain in the low resolution 21 cm images due the presence of residual sidelobes from bright sources. In the joint analysis of both frequencies, the radio halo has a 5.37 arcmin2 area with a 6.76 mJy flux density. Further observations and analysis are, however, required to fully characterize its properties.
- Full Text:
- Authors: Sichone, Gift L
- Date: 2020
- Subjects: Galaxies -- Clusters -- Observations , Radio astronomy -- Observations , Astrophysics -- South Africa , Westerbork Radio Telescope , A773 galaxy cluster , Astronomy -- Observations , Radio sources (Astronomy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144945 , vital:38394
- Description: In this thesis, we present 18 and 21 cm observations of the A773 galaxy cluster observed with the Westerbork radio telescope. The final 18 and 21 cm images achieve a noise level of 0.018 mJy beam‾ 1 and 0.025 mJy beam-1 respectively. After subtracting the compact sources, the low resolution images show evidence of a radio halo at 18 cm, whereas its presence is more uncertain in the low resolution 21 cm images due the presence of residual sidelobes from bright sources. In the joint analysis of both frequencies, the radio halo has a 5.37 arcmin2 area with a 6.76 mJy flux density. Further observations and analysis are, however, required to fully characterize its properties.
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Observations of diffuse radio emission in the Perseus Galaxy Cluster
- Authors: Mungwariri, Clemence
- Date: 2020
- Subjects: Galaxies -- Clusters , Radio sources (Astronomy) , Radio interferometers , Perseus Galaxy Cluster , Diffuse radio emission
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/143325 , vital:38233
- Description: In this thesis we analysed Westerbork observations of the Perseus Galaxy Cluster at 1380 MHz. Observations consist of two different pointings, covering a total of ∼ 0.5 square degrees, one including the known mini halo and the source 3C 84, the other centred on the source 3C 83.1 B. We obtained images with 83 μJy beam⁻¹ and 240 μJy beam⁻¹ noise rms for the two pointings respectively. We achieved a 60000 : 1 dynamic range in the image containing the bright 3C 84 source. We imaged the mini halo surrounding 3C 84 at high sensitivity, measuring its diameter to be ∼140 kpc and its power 4 x 10²⁴ W Hz⁻¹. Its morphology agrees quite well with that observed at 240 MHz (e.g. Gendron-Marsolais et al., 2017). We measured the flux density of 3C 84 to be 20.5 ± 0.4 Jy at the 2007 epoch, consistent with a factor of ∼2 increase since the 1960s.
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- Authors: Mungwariri, Clemence
- Date: 2020
- Subjects: Galaxies -- Clusters , Radio sources (Astronomy) , Radio interferometers , Perseus Galaxy Cluster , Diffuse radio emission
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/143325 , vital:38233
- Description: In this thesis we analysed Westerbork observations of the Perseus Galaxy Cluster at 1380 MHz. Observations consist of two different pointings, covering a total of ∼ 0.5 square degrees, one including the known mini halo and the source 3C 84, the other centred on the source 3C 83.1 B. We obtained images with 83 μJy beam⁻¹ and 240 μJy beam⁻¹ noise rms for the two pointings respectively. We achieved a 60000 : 1 dynamic range in the image containing the bright 3C 84 source. We imaged the mini halo surrounding 3C 84 at high sensitivity, measuring its diameter to be ∼140 kpc and its power 4 x 10²⁴ W Hz⁻¹. Its morphology agrees quite well with that observed at 240 MHz (e.g. Gendron-Marsolais et al., 2017). We measured the flux density of 3C 84 to be 20.5 ± 0.4 Jy at the 2007 epoch, consistent with a factor of ∼2 increase since the 1960s.
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A pilot wide-field VLBI survey of the GOODS-North field
- Authors: Akoto-Danso, Alexander
- Date: 2019
- Subjects: Radio astronomy , Very long baseline interferometry , Radio interometers , Imaging systems in astronomy , Hubble Space Telescope (Spacecraft) -- Observations
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/72296 , vital:30027
- Description: Very Long Baseline Interferometry (VLBI) has significant advantages in disentangling active galactic nuclei (AGN) from star formation, particularly at intermediate to high-redshift due to its high angular resolution and insensitivity to dust. Surveys using VLBI arrays are only just becoming practical over wide areas with numerous developments and innovations (such as multi-phase centre techniques) in observation and data analysis techniques. However, fully automated pipelines for VLBI data analysis are based on old software packages and are unable to incorporate new calibration and imaging algorithms. In this work, the researcher developed a pipeline for VLBI data analysis which integrates a recent wide-field imaging algorithm, RFI excision, and a purpose-built source finding algorithm specifically developed for the 64kx64k wide-field VLBI images. The researcher used this novel pipeline to process 6% (~ 9 arcmin2 of the total 160 arcmin2) of the data from the CANDELS GOODS- North extragalactic field at 1.6 GHz. The milli-arcsec scale images have an average rms of a ~ 10 uJy/beam. Forty four (44) candidate sources were detected, most of which are at sub-mJy flux densities, having brightness temperatures and luminosities of >5x105 K and >6x1021 W Hz-1 respectively. This work demonstrates that automated post-processing pipelines for wide-field, uniform sensitivity VLBI surveys are feasible and indeed made more efficient with new software, wide-field imaging algorithms and more purpose-built source- finders. This broadens the discovery space for future wide-field surveys with upcoming arrays such as the African VLBI Network (AVN), MeerKAT and the Square Kilometre Array (SKA).
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- Authors: Akoto-Danso, Alexander
- Date: 2019
- Subjects: Radio astronomy , Very long baseline interferometry , Radio interometers , Imaging systems in astronomy , Hubble Space Telescope (Spacecraft) -- Observations
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/72296 , vital:30027
- Description: Very Long Baseline Interferometry (VLBI) has significant advantages in disentangling active galactic nuclei (AGN) from star formation, particularly at intermediate to high-redshift due to its high angular resolution and insensitivity to dust. Surveys using VLBI arrays are only just becoming practical over wide areas with numerous developments and innovations (such as multi-phase centre techniques) in observation and data analysis techniques. However, fully automated pipelines for VLBI data analysis are based on old software packages and are unable to incorporate new calibration and imaging algorithms. In this work, the researcher developed a pipeline for VLBI data analysis which integrates a recent wide-field imaging algorithm, RFI excision, and a purpose-built source finding algorithm specifically developed for the 64kx64k wide-field VLBI images. The researcher used this novel pipeline to process 6% (~ 9 arcmin2 of the total 160 arcmin2) of the data from the CANDELS GOODS- North extragalactic field at 1.6 GHz. The milli-arcsec scale images have an average rms of a ~ 10 uJy/beam. Forty four (44) candidate sources were detected, most of which are at sub-mJy flux densities, having brightness temperatures and luminosities of >5x105 K and >6x1021 W Hz-1 respectively. This work demonstrates that automated post-processing pipelines for wide-field, uniform sensitivity VLBI surveys are feasible and indeed made more efficient with new software, wide-field imaging algorithms and more purpose-built source- finders. This broadens the discovery space for future wide-field surveys with upcoming arrays such as the African VLBI Network (AVN), MeerKAT and the Square Kilometre Array (SKA).
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Foreground simulations for observations of the global 21-cm signal
- Authors: Klutse, Diana
- Date: 2019
- Subjects: Cosmic background radiation , Astronomy -- Observations , Electromagnetic waves , Radiation, Background
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76398 , vital:30557
- Description: The sky-averaged (global) spectrum of the redshifted 21-cm line promises to be a direct probe of the Dark Ages, the period before the first luminous sources formed and the Epoch of Reionization during which these sources produced enough ionizing photons to ionize the neutral intergalactic medium. However, observations of this signal are contaminated by both astrophysical foregrounds which are orders of magnitude brighter than the cosmological signal and by non-astrophysical and non-ideal instrumental effects. It is therefore crucial to understand all these data components and their impacts on the cosmological signal, for successful signal extraction. In this view, we investigated the impact that small scale spatial structures of diffuse Galactic foreground has on the foreground spectrum as observed by a global 21-cm observation. We simulated two different sets of observations using a realistic dipole beam model of two synchotron foreground templates that differ from each other in the small scale structure: the original 408 MHz all-sky map by Haslam et al. (1982) and a version where the calibration was improved to remove artifcats and point sources (Remazeilles et al., 2015). We generated simulated foreground spectra and modeled them using a polynomial expansion in frequency. We found that the different foreground templates have a modest impact on the simulated spectra, generate differences up to 2% in the root mean square of residual spectra after the log-polynomial best fit was subtracted out.
- Full Text:
- Authors: Klutse, Diana
- Date: 2019
- Subjects: Cosmic background radiation , Astronomy -- Observations , Electromagnetic waves , Radiation, Background
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76398 , vital:30557
- Description: The sky-averaged (global) spectrum of the redshifted 21-cm line promises to be a direct probe of the Dark Ages, the period before the first luminous sources formed and the Epoch of Reionization during which these sources produced enough ionizing photons to ionize the neutral intergalactic medium. However, observations of this signal are contaminated by both astrophysical foregrounds which are orders of magnitude brighter than the cosmological signal and by non-astrophysical and non-ideal instrumental effects. It is therefore crucial to understand all these data components and their impacts on the cosmological signal, for successful signal extraction. In this view, we investigated the impact that small scale spatial structures of diffuse Galactic foreground has on the foreground spectrum as observed by a global 21-cm observation. We simulated two different sets of observations using a realistic dipole beam model of two synchotron foreground templates that differ from each other in the small scale structure: the original 408 MHz all-sky map by Haslam et al. (1982) and a version where the calibration was improved to remove artifcats and point sources (Remazeilles et al., 2015). We generated simulated foreground spectra and modeled them using a polynomial expansion in frequency. We found that the different foreground templates have a modest impact on the simulated spectra, generate differences up to 2% in the root mean square of residual spectra after the log-polynomial best fit was subtracted out.
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Observing cosmic reionization with PAPER: polarized foreground simulations and all sky images
- Authors: Nunhokee, Chuneeta Devi
- Date: 2019
- Subjects: Cosmic background radiation , Astronomy -- Observations , Epoch of reionization -- Research , Hydrogen -- Spectra , Radio interferometers
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/68203 , vital:29218
- Description: The Donald C. Backer Precision Array to Probe the Epoch of Reionization (PAPER, Parsons et al., 2010) was built with an aim to detect the redshifted 21 cm Hydrogen line, which is likely the best probe of thermal evolution of the intergalactic medium and reionization of neutral Hydrogen in our Universe. Observations of the 21 cm signal are challenged by bright astrophysical foregrounds and systematics that require precise modeling in order to extract the cosmological signal. In particular, the instrumental leakage of polarized foregrounds may contaminate the 21 cm power spectrum. In this work, we developed a formalism to describe the leakage due to instrumental widefield effects in visibility-based power spectra and used it to predict contaminations in observations. We find the leakage due to a population of point sources to be higher than the diffuse Galactic emission – for which we can predict minimal contaminations at k>0.3 h Mpc -¹ We also analyzed data from the last observing season of PAPER via all-sky imaging with a view to characterize the foregrounds. We generated an all-sky catalogue of 88 sources down to a flux density of 5 Jy. Moreover, we measured both polarized point source and the Galactic diffuse emission, and used these measurements to constrain our model of polarization leakage. We find the leakage due to a population of point sources to be 12% lower than the prediction from our polarized model.
- Full Text:
- Authors: Nunhokee, Chuneeta Devi
- Date: 2019
- Subjects: Cosmic background radiation , Astronomy -- Observations , Epoch of reionization -- Research , Hydrogen -- Spectra , Radio interferometers
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/68203 , vital:29218
- Description: The Donald C. Backer Precision Array to Probe the Epoch of Reionization (PAPER, Parsons et al., 2010) was built with an aim to detect the redshifted 21 cm Hydrogen line, which is likely the best probe of thermal evolution of the intergalactic medium and reionization of neutral Hydrogen in our Universe. Observations of the 21 cm signal are challenged by bright astrophysical foregrounds and systematics that require precise modeling in order to extract the cosmological signal. In particular, the instrumental leakage of polarized foregrounds may contaminate the 21 cm power spectrum. In this work, we developed a formalism to describe the leakage due to instrumental widefield effects in visibility-based power spectra and used it to predict contaminations in observations. We find the leakage due to a population of point sources to be higher than the diffuse Galactic emission – for which we can predict minimal contaminations at k>0.3 h Mpc -¹ We also analyzed data from the last observing season of PAPER via all-sky imaging with a view to characterize the foregrounds. We generated an all-sky catalogue of 88 sources down to a flux density of 5 Jy. Moreover, we measured both polarized point source and the Galactic diffuse emission, and used these measurements to constrain our model of polarization leakage. We find the leakage due to a population of point sources to be 12% lower than the prediction from our polarized model.
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MEQSILHOUETTE: a mm-VLBI observation and signal corruption simulator
- Authors: Blecher, Tariq
- Date: 2017
- Subjects: Large astronomical telescopes , Very long baseline interferometry , MEQSILHOUETTE (Software) , Event horizon telescope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/40713 , vital:25019
- Description: The Event Horizon Telescope (EHT) aims to resolve the innermost emission of nearby supermassive black holes, Sgr A* and M87, on event horizon scales. This emission is predicted to be gravitationally lensed by the black hole which should produce a shadow (or silhouette) feature, a precise measurement of which is a test of gravity in the strong-field regime. This emission is also an ideal probe of the innermost accretion and jet-launch physics, offering the new insights into this data-limited observing regime. The EHT will use the technique of Very Long Baseline Interferometry (VLBI) at (sub)millimetre wavelengths, which has a diffraction limited angular resolution of order ~ 10 µ-arcsec. However, this technique suffers from unique challenges, including scattering and attenuation in the troposphere and interstellar medium; variable source structure; as well as antenna pointing errors comparable to the size of the primary beam. In this thesis, we present the meqsilhouette software package which is focused towards simulating realistic EHT data. It has the capability to simulate a time-variable source, and includes realistic descriptions of the effects of the troposphere, the interstellar medium as well as primary beams and associated antenna pointing errors. We have demonstrated through several examples simulations that these effects can limit the ability to measure the key science parameters. This simulator can be used to research calibration, parameter estimation and imaging strategies, as well as gain insight into possible systematic uncertainties.
- Full Text:
- Authors: Blecher, Tariq
- Date: 2017
- Subjects: Large astronomical telescopes , Very long baseline interferometry , MEQSILHOUETTE (Software) , Event horizon telescope
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/40713 , vital:25019
- Description: The Event Horizon Telescope (EHT) aims to resolve the innermost emission of nearby supermassive black holes, Sgr A* and M87, on event horizon scales. This emission is predicted to be gravitationally lensed by the black hole which should produce a shadow (or silhouette) feature, a precise measurement of which is a test of gravity in the strong-field regime. This emission is also an ideal probe of the innermost accretion and jet-launch physics, offering the new insights into this data-limited observing regime. The EHT will use the technique of Very Long Baseline Interferometry (VLBI) at (sub)millimetre wavelengths, which has a diffraction limited angular resolution of order ~ 10 µ-arcsec. However, this technique suffers from unique challenges, including scattering and attenuation in the troposphere and interstellar medium; variable source structure; as well as antenna pointing errors comparable to the size of the primary beam. In this thesis, we present the meqsilhouette software package which is focused towards simulating realistic EHT data. It has the capability to simulate a time-variable source, and includes realistic descriptions of the effects of the troposphere, the interstellar medium as well as primary beams and associated antenna pointing errors. We have demonstrated through several examples simulations that these effects can limit the ability to measure the key science parameters. This simulator can be used to research calibration, parameter estimation and imaging strategies, as well as gain insight into possible systematic uncertainties.
- Full Text:
Calibration and wide field imaging with PAPER: a catalogue of compact sources
- Authors: Philip, Liju
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2397 , vital:20285
- Description: Observations of the redshifted 21 cm HI line promise to be a formidable tool for cosmology, allowing the investigation of the end of the so-called dark ages, when the first galaxies formed, and the subsequent Epoch of Reionization when the intergalactic medium transitioned from neutral to ionized. Such observations are plagued by foreground emission which is a few orders of magnitude brighter than the 21 cm line. In this thesis I analyzed data from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in order to improve the characterization of the extragalactic foreground component. I derived a catalogue of unresolved radio sources down to a 5 Jy flux density limit at 150 MHz and derived their spectral index distribution using literature data at 408 MHz. I implemented advanced techniques to calibrate radio interferometric data that led to a few percent accuracy on the flux density scale of the derived catalogue. This work, therefore, represents a further step towards creating an accurate, global sky model that is crucial to improve calibration of Epoch of Reionization observations.
- Full Text:
- Authors: Philip, Liju
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2397 , vital:20285
- Description: Observations of the redshifted 21 cm HI line promise to be a formidable tool for cosmology, allowing the investigation of the end of the so-called dark ages, when the first galaxies formed, and the subsequent Epoch of Reionization when the intergalactic medium transitioned from neutral to ionized. Such observations are plagued by foreground emission which is a few orders of magnitude brighter than the 21 cm line. In this thesis I analyzed data from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in order to improve the characterization of the extragalactic foreground component. I derived a catalogue of unresolved radio sources down to a 5 Jy flux density limit at 150 MHz and derived their spectral index distribution using literature data at 408 MHz. I implemented advanced techniques to calibrate radio interferometric data that led to a few percent accuracy on the flux density scale of the derived catalogue. This work, therefore, represents a further step towards creating an accurate, global sky model that is crucial to improve calibration of Epoch of Reionization observations.
- Full Text:
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