Is the observed high-frequency radio luminosity distribution of QSOs bimodal?
The distribution of QSO radio luminosities has long been debated in the literature. Some argue that it is a bimodal distribution, implying that there are two separate QSO populations (normally referred to as ‘radio-loud’ and ‘radio-quiet’), while others claim it forms a more continuous distribution...
| Main Authors: | , , , , , |
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| Format: | Journal Article |
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Institute of Physics Publishing, Inc.
2012
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| Subjects: | |
| Online Access: | http://hdl.handle.net/20.500.11937/38929 |
| _version_ | 1848755452627648512 |
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| author | Mahony, E. Sadler, E. Croom, S. Ekers, Ronald Feain, I. Murphy, T. |
| author_facet | Mahony, E. Sadler, E. Croom, S. Ekers, Ronald Feain, I. Murphy, T. |
| author_sort | Mahony, E. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | The distribution of QSO radio luminosities has long been debated in the literature. Some argue that it is a bimodal distribution, implying that there are two separate QSO populations (normally referred to as ‘radio-loud’ and ‘radio-quiet’), while others claim it forms a more continuous distribution characteristic of a single population. We use deep observations at 20GHz to investigate whether the distribution is bimodal at high radio frequencies. Carrying out this study at high radio frequencies has an advantage over previous studies as the radio emission comes predominantly from the core of the AGN, hence probes the most recent activity. Studies carried out at lower frequencies are dominated by the large scale lobes where the emission is built up over longer timescales (107 − 108 yrs), thereby confusing the sample. Our sample comprises 874 X-ray selected QSOs that were observed as part of the 6dF Galaxy Survey. Of these, 40% were detected down to a 3 detection limit of 0.2–0.5mJy. No evidence of bimodality is seen in either the 20GHz luminosity distribution or in the distribution of the R20 parameter: the ratio of the radio to optical luminosities traditionally used to classify objects as being either radio-loud or radio-quiet. Previous results have claimed that at low radio luminosities, star formation processes can dominate the radio emission observed in QSOs. We attempt to investigate these claims by stacking the undetected sources at 20GHz and discuss the limitations in carrying out this analysis. However, if the radio emission was solely due to star formation processes, we calculate that this corresponds to star formation rates ranging from ~10 solar masses/yr to ~2300 solar masses/yr. |
| first_indexed | 2025-11-14T08:56:32Z |
| format | Journal Article |
| id | curtin-20.500.11937-38929 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:56:32Z |
| publishDate | 2012 |
| publisher | Institute of Physics Publishing, Inc. |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-389292017-09-13T14:20:53Z Is the observed high-frequency radio luminosity distribution of QSOs bimodal? Mahony, E. Sadler, E. Croom, S. Ekers, Ronald Feain, I. Murphy, T. quasars: general galaxies: star formation galaxies: active radio continuum: galaxies The distribution of QSO radio luminosities has long been debated in the literature. Some argue that it is a bimodal distribution, implying that there are two separate QSO populations (normally referred to as ‘radio-loud’ and ‘radio-quiet’), while others claim it forms a more continuous distribution characteristic of a single population. We use deep observations at 20GHz to investigate whether the distribution is bimodal at high radio frequencies. Carrying out this study at high radio frequencies has an advantage over previous studies as the radio emission comes predominantly from the core of the AGN, hence probes the most recent activity. Studies carried out at lower frequencies are dominated by the large scale lobes where the emission is built up over longer timescales (107 − 108 yrs), thereby confusing the sample. Our sample comprises 874 X-ray selected QSOs that were observed as part of the 6dF Galaxy Survey. Of these, 40% were detected down to a 3 detection limit of 0.2–0.5mJy. No evidence of bimodality is seen in either the 20GHz luminosity distribution or in the distribution of the R20 parameter: the ratio of the radio to optical luminosities traditionally used to classify objects as being either radio-loud or radio-quiet. Previous results have claimed that at low radio luminosities, star formation processes can dominate the radio emission observed in QSOs. We attempt to investigate these claims by stacking the undetected sources at 20GHz and discuss the limitations in carrying out this analysis. However, if the radio emission was solely due to star formation processes, we calculate that this corresponds to star formation rates ranging from ~10 solar masses/yr to ~2300 solar masses/yr. 2012 Journal Article http://hdl.handle.net/20.500.11937/38929 10.1088/0004-637X/754/1/12 Institute of Physics Publishing, Inc. unknown |
| spellingShingle | quasars: general galaxies: star formation galaxies: active radio continuum: galaxies Mahony, E. Sadler, E. Croom, S. Ekers, Ronald Feain, I. Murphy, T. Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title | Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title_full | Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title_fullStr | Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title_full_unstemmed | Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title_short | Is the observed high-frequency radio luminosity distribution of QSOs bimodal? |
| title_sort | is the observed high-frequency radio luminosity distribution of qsos bimodal? |
| topic | quasars: general galaxies: star formation galaxies: active radio continuum: galaxies |
| url | http://hdl.handle.net/20.500.11937/38929 |