The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs
We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the pres...
| Main Authors: | , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
2005
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| _version_ | 1797075262091821056 |
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| author | Wall, J Jackson, C Shaver, P Hook, I Kellermann, K |
| author_facet | Wall, J Jackson, C Shaver, P Hook, I Kellermann, K |
| author_sort | Wall, J |
| collection | OXFORD |
| description | We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths. © ESO 2005. |
| first_indexed | 2024-03-06T23:47:57Z |
| format | Journal article |
| id | oxford-uuid:71985fab-f9c5-414d-ad85-e51d01e1df4c |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T23:47:57Z |
| publishDate | 2005 |
| record_format | dspace |
| spelling | oxford-uuid:71985fab-f9c5-414d-ad85-e51d01e1df4c2022-03-26T19:44:40ZThe Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:71985fab-f9c5-414d-ad85-e51d01e1df4cEnglishSymplectic Elements at Oxford2005Wall, JJackson, CShaver, PHook, IKellermann, KWe analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths. © ESO 2005. |
| spellingShingle | Wall, J Jackson, C Shaver, P Hook, I Kellermann, K The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title | The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title_full | The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title_fullStr | The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title_full_unstemmed | The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title_short | The Parkes quarter-Jansky flat-spectrum sample - III. Space density and evolution of QSOs |
| title_sort | parkes quarter jansky flat spectrum sample iii space density and evolution of qsos |
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