Luminosity functions using new radio surveys
<p>Galaxy evolution at radio wavelengths is often measured using luminosity functions which are commonly based on the luminosity (L) and redshift (z) of individual sources as well as the overall distribution for a sample. However, an important factor when K-correcting radio sources to their r...
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| Formato: | Thesis |
| Idioma: | English |
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2019
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| _version_ | 1826287848779677696 |
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| author | Peters, J |
| author2 | Jarvis, M |
| author_facet | Jarvis, M Peters, J |
| author_sort | Peters, J |
| collection | OXFORD |
| description | <p>Galaxy evolution at radio wavelengths is often measured using luminosity functions which are commonly based on the luminosity (L) and redshift (z) of individual sources as well as the overall distribution for a sample. However, an important factor when K-correcting radio sources to their rest-frame luminosity is the spectral index (α). This is often assumed to be a constant value for the entire sample. In reality, there is a distributioninαwhich affects the rate at which sources drop below the flux limit of thesurvey. If not accounted for, the differing rates at which sources become unobservable can be mistaken as a genuine decline in source numbers and affect the evolution of the radio luminosity function (RLF).</p>
<p>To tackle this, I estimate RLFs incorporating theα-distribution for both active galactic nuclei (AGN) and star forming galaxies (SFGs). Data from the Low-Frequency Array (LOFAR) and the Very Large Array (VLA) are used to formulate 150 MHz RLFs for a sample of AGN. MeerKAT and VLA data are used to measure and model the 1.4 GHz RLFs for a sample of SFGs. Markov Chain Monte Carlo sampling is used to find parameters to fit models based onρ(L,z) andρ(L,z,α) for comparison.The main findings of this work are that the accurate modelling of theα-distribution has a significant effect on not only the shape of the RLF,but the value of the evolution parameter k, parameterised as (1 +z)k in pure evolution and pure density evolution. This is true for both AGN and SFGs.</p>
<p>The AGN RLF model has higher values of k when accounting for theα-distribution. Steep spectrum sources drop out of the flux limit of a survey earlier and therefore drive the RLF to evolve faster.</p>
<p>The SFG RLF model has lower values of k when α is accounted for, since high values of k are found to compensate for the absence ofαinformation.Since the aim of RLFs is to measure the evolution of galaxies, it is imperative that the α-distribution be included to obtain accurate estimates of the strength of any evolution.</p>
<p>Future work would aim to improve on this further through including an-other factor that affects the visibility of a source; the angular or projected linear size of the source. In this thesis, observations of the same field but using different antenna configurations have shown that high-resolution,long baseline imaging needs to be supplemented with short baseline observations to fully capture all scales of emission and all sources. Therefore, a radio telescope with an abundance of both short and long baselines is necessary. MeerKAT is such a telescope, as will be the SKA. Therefore, my work has set out the way forward for towards properly understanding the evolution of radio sources in the Universe.</p> |
| first_indexed | 2024-03-07T02:04:49Z |
| format | Thesis |
| id | oxford-uuid:9e9df12c-c9ec-4bfc-88f8-a4299f5c384d |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T02:04:49Z |
| publishDate | 2019 |
| record_format | dspace |
| spelling | oxford-uuid:9e9df12c-c9ec-4bfc-88f8-a4299f5c384d2022-03-27T00:51:25ZLuminosity functions using new radio surveysThesishttp://purl.org/coar/resource_type/c_db06uuid:9e9df12c-c9ec-4bfc-88f8-a4299f5c384dGalaxy evolutionAstronomyGalaxiesAstrophysicsActive galaxiesInterferometryRadio astronomyRadio telescopesEnglishHyrax Deposit2019Peters, JJarvis, M<p>Galaxy evolution at radio wavelengths is often measured using luminosity functions which are commonly based on the luminosity (L) and redshift (z) of individual sources as well as the overall distribution for a sample. However, an important factor when K-correcting radio sources to their rest-frame luminosity is the spectral index (α). This is often assumed to be a constant value for the entire sample. In reality, there is a distributioninαwhich affects the rate at which sources drop below the flux limit of thesurvey. If not accounted for, the differing rates at which sources become unobservable can be mistaken as a genuine decline in source numbers and affect the evolution of the radio luminosity function (RLF).</p> <p>To tackle this, I estimate RLFs incorporating theα-distribution for both active galactic nuclei (AGN) and star forming galaxies (SFGs). Data from the Low-Frequency Array (LOFAR) and the Very Large Array (VLA) are used to formulate 150 MHz RLFs for a sample of AGN. MeerKAT and VLA data are used to measure and model the 1.4 GHz RLFs for a sample of SFGs. Markov Chain Monte Carlo sampling is used to find parameters to fit models based onρ(L,z) andρ(L,z,α) for comparison.The main findings of this work are that the accurate modelling of theα-distribution has a significant effect on not only the shape of the RLF,but the value of the evolution parameter k, parameterised as (1 +z)k in pure evolution and pure density evolution. This is true for both AGN and SFGs.</p> <p>The AGN RLF model has higher values of k when accounting for theα-distribution. Steep spectrum sources drop out of the flux limit of a survey earlier and therefore drive the RLF to evolve faster.</p> <p>The SFG RLF model has lower values of k when α is accounted for, since high values of k are found to compensate for the absence ofαinformation.Since the aim of RLFs is to measure the evolution of galaxies, it is imperative that the α-distribution be included to obtain accurate estimates of the strength of any evolution.</p> <p>Future work would aim to improve on this further through including an-other factor that affects the visibility of a source; the angular or projected linear size of the source. In this thesis, observations of the same field but using different antenna configurations have shown that high-resolution,long baseline imaging needs to be supplemented with short baseline observations to fully capture all scales of emission and all sources. Therefore, a radio telescope with an abundance of both short and long baselines is necessary. MeerKAT is such a telescope, as will be the SKA. Therefore, my work has set out the way forward for towards properly understanding the evolution of radio sources in the Universe.</p> |
| spellingShingle | Galaxy evolution Astronomy Galaxies Astrophysics Active galaxies Interferometry Radio astronomy Radio telescopes Peters, J Luminosity functions using new radio surveys |
| title | Luminosity functions using new radio surveys |
| title_full | Luminosity functions using new radio surveys |
| title_fullStr | Luminosity functions using new radio surveys |
| title_full_unstemmed | Luminosity functions using new radio surveys |
| title_short | Luminosity functions using new radio surveys |
| title_sort | luminosity functions using new radio surveys |
| topic | Galaxy evolution Astronomy Galaxies Astrophysics Active galaxies Interferometry Radio astronomy Radio telescopes |
| work_keys_str_mv | AT petersj luminosityfunctionsusingnewradiosurveys |