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).
- Full Text:
- Date Issued: 2019
- 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).
- Full Text:
- Date Issued: 2019
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:
- Date Issued: 2019
- 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:
- Date Issued: 2019
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