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Theses

Evolution de la structure VLBI des sources de l'ICRF : lien entre astrométrie et astrophysique

Abstract : Active Galactic Nuclei (AGN) are located in the center of extremely distant and bright galaxies. Their luminosity comes from the interaction between a super-massive central blackhole and an accretion disk, producing a relativistic collimated jet of matter. Thanks to the extremely high resolution achieved by Very Long Base line Interferometry (VLBI), the jet structure may be studied in detail, while the astrometric position of the AGN is determined with ahigh accuracy. Because of their location at cosmological distances, no proper motions are detected for those objects, making them ideal fiducial points for building highly-precise celestial reference frames.Instabilities up to a few hundreds of micro arc seconds are yet often observed in astrometricpositions on time scales from months to years. This is generally thought to be caused by theevolution of source structure. The study presented here investigates the correlation between the two phenomena on a statistical basis. Based on regular VLBI observations conducted between1994 and 2003, astrometric position variations and source structure evolution are compared fora sample of 68 AGN over a period of 10 years. The results indicate that a correlation between the two phenomena does exist but it is not as strong as expected. Additionally, a simulation of the effects caused by the precession of the accretion disc and the potential presence of abinary black hole in the center of the AGN is presented. Applied to the source 1308+326, the simulation shows that the magnitude of the effects is consistent with the oscillations of the jet trajectory observed on VLBI scale.
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Submitted on : Thursday, October 1, 2015 - 10:13:08 AM
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Romuald Bouffet. Evolution de la structure VLBI des sources de l'ICRF : lien entre astrométrie et astrophysique. Astrophysique [astro-ph]. Université de Bordeaux, 2015. Français. ⟨NNT : 2015BORD0083⟩. ⟨tel-01207646⟩

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