DUAL-FREQUENCY OBSERVATIONS OF 140 COMPACT, FLAT-SPECTRUM ACTIVE GALACTIC NUCLEI FOR SCINTILLATION-INDUCED VARIABILITY
| dc.contributor.author | Koay, J. Y. | |
| dc.contributor.author | Macquart, J.-P. | |
| dc.contributor.author | Rickett, B. J. | |
| dc.contributor.author | Bignall, H. E. | |
| dc.contributor.author | Lovell, J. E. J. | |
| dc.contributor.author | Reynolds, C. | |
| dc.contributor.author | Jauncey, D. L. | |
| dc.contributor.author | Pursimo, T. | |
| dc.contributor.author | Kedziora-Chudczer, L. | |
| dc.contributor.author | Ojha, R. | |
| dc.date.accessioned | 2020-04-01T13:14:58Z | |
| dc.date.available | 2020-04-01T13:14:58Z | |
| dc.date.issued | 2011-08-30 | |
| dc.description.abstract | The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey detected a drop in interstellar scintillation (ISS) for sources at redshifts z gsim 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. | en_US |
| dc.description.sponsorship | J. Y. Koay is supported by the Curtin Strategic International Research Scholarship (CSIRS) provided by Curtin University, and thanks Professor Ron Ekers of CSIRO and Greg Taylor of the University of New Mexico for helpful discussions. B. J. Rickett thanks the National Science Foundation (NSF) for partial support under grant AST-0507713. R. Ojha is supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. We all thank the operators and scientific staff at the Very Large Array; in particular, we thank Vivek Dhawan for his extensive advice and help during our long sequence of observations. The VLA is part of the National Radio Astronomy Observatory (NRAO), which is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. This study made use of data from the Wisconsin H-Alpha Mapper (WHAM) survey, which is funded by the NSF. Data were also obtained from the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. | en_US |
| dc.description.uri | https://iopscience.iop.org/article/10.1088/0004-6256/142/4/108 | en_US |
| dc.format.extent | 21 pages | en_US |
| dc.genre | journal articles | en_US |
| dc.identifier | doi:10.13016/m2mpft-v8gs | |
| dc.identifier.citation | J. Y. Koay,J.-P. Macquart,B. J. Rickett,H. E. Bignall,J. E. J. Lovell,C. Reynolds,D. L. Jauncey,T. Pursimo,L. Kedziora-Chudczer,R. Ojha, DUAL-FREQUENCY OBSERVATIONS OF 140 COMPACT FLAT-SPECTRUM ACTIVE GALAhttps://iopscience.iop.org/article/10.1088/0004-6256/142/4/108CTIC NUCLEI FOR SCINTILLATION-INDUCED VARIABILITY, | en_US |
| dc.identifier.uri | http://hdl.handle.net/11603/17786 | |
| dc.identifier.uri | http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2011AJ....142..108K | |
| dc.identifier.uri | https://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Search&refcode=2011AJ....142..108K | |
| dc.identifier.uri | http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/AJ/142/108 | |
| dc.language.iso | en_US | en_US |
| dc.publisher | IOP | en_US |
| dc.relation.isAvailableAt | The University of Maryland, Baltimore County (UMBC) | |
| dc.relation.ispartof | UMBC Physics Department Collection | |
| dc.relation.ispartof | UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II) | |
| dc.rights | This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author. | |
| dc.rights | © 2011. The American Astronomical Society. All rights reserved. | |
| dc.title | DUAL-FREQUENCY OBSERVATIONS OF 140 COMPACT, FLAT-SPECTRUM ACTIVE GALACTIC NUCLEI FOR SCINTILLATION-INDUCED VARIABILITY | en_US |
| dc.type | Text | en_US |