Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability
The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z "greater than approximately 2", indicating an apparent increase in angular diameter or a decrease in flux density of the most compact...
| Main Authors: | , , , , , , , , , |
|---|---|
| Format: | Journal Article |
| Published: |
Institute of Physics Publishing, Inc
2011
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/20.500.11937/38096 |
| _version_ | 1848755227171225600 |
|---|---|
| author | Koay, J. Macquart, Jean-Pierre Rickett, B.J. Bignall, Hayley Lovell, J. E. J. Reynolds, Cormac Jauncey, D. L. Pursimo, T. Kedziora-Chudczer, L. Ojha, R. |
| author_facet | Koay, J. Macquart, Jean-Pierre Rickett, B.J. Bignall, Hayley Lovell, J. E. J. Reynolds, Cormac Jauncey, D. L. Pursimo, T. Kedziora-Chudczer, L. Ojha, R. |
| author_sort | Koay, J. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z "greater than approximately 2", indicating an apparent increase in angular diameter or a decrease in flux density of the most compact components of these sources relative to their extended emission. This can result from intrinsic source size effects or scatter broadening in the intergalactic medium (IGM) in excess of the expected (1 + z)1/2 angular diameter scaling of brightness temperature limited sources resulting from cosmological expansion. We report here 4.9 GHz and 8.4 GHz observations and data analysis for a sample of 140 compact, flat-spectrum sources which may allow us to determine the origin of this angular diameter-redshift relation by exploiting their different wavelength dependences. In addition to using ISS as a cosmological probe, the observations provide additional insight into source morphologies and the characteristics of ISS. As in the MASIV Survey, the variability of the sources is found to be significantly correlated with line-of-sight Hα intensities, confirming its link with ISS. For 25 sources, time delays of about 0.15-3 days are observed between the scintillation patterns at both frequencies, interpreted as being caused by a shift in core positions when probed at different optical depths.Significant correlation is found between ISS amplitudes and source spectral index; in particular, a large drop in ISS amplitudes is observed at α < –0.4 confirming that steep spectrum sources scintillate less. We detect a weakened redshift dependence of ISS at 8.4 GHz over that at 4.9 GHz, with the mean variance at four-day timescales reduced by a factor of 1.8 in the z > 2 sources relative to the z < 2 sources, as opposed to the factor of three decrease observed at 4.9 GHz. This suggests scatter broadening in the IGM, but the interpretation is complicated by subtle selection effects that will be explored further in a follow-up paper. |
| first_indexed | 2025-11-14T08:52:57Z |
| format | Journal Article |
| id | curtin-20.500.11937-38096 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:52:57Z |
| publishDate | 2011 |
| publisher | Institute of Physics Publishing, Inc |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-380962017-09-13T15:38:03Z Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability Koay, J. Macquart, Jean-Pierre Rickett, B.J. Bignall, Hayley Lovell, J. E. J. Reynolds, Cormac Jauncey, D. L. Pursimo, T. Kedziora-Chudczer, L. Ojha, R. quasars: general ISM: structure methods: data analysis radio continuum: ISM galaxies: active intergalactic medium The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z "greater than approximately 2", indicating an apparent increase in angular diameter or a decrease in flux density of the most compact components of these sources relative to their extended emission. This can result from intrinsic source size effects or scatter broadening in the intergalactic medium (IGM) in excess of the expected (1 + z)1/2 angular diameter scaling of brightness temperature limited sources resulting from cosmological expansion. We report here 4.9 GHz and 8.4 GHz observations and data analysis for a sample of 140 compact, flat-spectrum sources which may allow us to determine the origin of this angular diameter-redshift relation by exploiting their different wavelength dependences. In addition to using ISS as a cosmological probe, the observations provide additional insight into source morphologies and the characteristics of ISS. As in the MASIV Survey, the variability of the sources is found to be significantly correlated with line-of-sight Hα intensities, confirming its link with ISS. For 25 sources, time delays of about 0.15-3 days are observed between the scintillation patterns at both frequencies, interpreted as being caused by a shift in core positions when probed at different optical depths.Significant correlation is found between ISS amplitudes and source spectral index; in particular, a large drop in ISS amplitudes is observed at α < –0.4 confirming that steep spectrum sources scintillate less. We detect a weakened redshift dependence of ISS at 8.4 GHz over that at 4.9 GHz, with the mean variance at four-day timescales reduced by a factor of 1.8 in the z > 2 sources relative to the z < 2 sources, as opposed to the factor of three decrease observed at 4.9 GHz. This suggests scatter broadening in the IGM, but the interpretation is complicated by subtle selection effects that will be explored further in a follow-up paper. 2011 Journal Article http://hdl.handle.net/20.500.11937/38096 10.1088/0004-6256/142/4/108 Institute of Physics Publishing, Inc fulltext |
| spellingShingle | quasars: general ISM: structure methods: data analysis radio continuum: ISM galaxies: active intergalactic medium Koay, J. Macquart, Jean-Pierre Rickett, B.J. Bignall, Hayley Lovell, J. E. J. Reynolds, Cormac Jauncey, D. L. Pursimo, T. Kedziora-Chudczer, L. Ojha, R. Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title | Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title_full | Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title_fullStr | Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title_full_unstemmed | Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title_short | Dual-frequency Observations of 140 Compact, Flat-spectrum Active Galactic Nuclei for Scintillation-induced Variability |
| title_sort | dual-frequency observations of 140 compact, flat-spectrum active galactic nuclei for scintillation-induced variability |
| topic | quasars: general ISM: structure methods: data analysis radio continuum: ISM galaxies: active intergalactic medium |
| url | http://hdl.handle.net/20.500.11937/38096 |