Multi-Epoch Millimeter VLBI Observations of the Twin-Jet System in NGC1052

This Master thesis reports on a detailed analysis of the emission from the center of the active galaxy NGC 1052 at 22, 43, and 86GHz. The active galactic nucleus (AGN) of this elliptical galaxy hosts two radio-emitting jets with an unresolved emission gap in between at lower frequencies. This gap can be explained by an absorbing torus. Due to its distance of about 19 Mpc, the innermost structure can be analyzed in great detail with millimeter-wavelength very-long-baseline interferometry (VLBI). AGNs are known for strong emission over the whole electromagnetic spectrum. To explain the high energy output a super massive black hole (SMBH) is thought to be located at the center. A unified scheme was developed to describe most aspects seen in different classes of AGN, but the underlying physical processes are not completely understood, yet. The low luminosity AGN NGC1052 is an excellent source to test current jet models, thanks to its orientation near to the plane of the sky and the observed twin-jet structure. Observations at 3mm wavelength reveal a strong central feature, smaller than 8. 6μas along the jet angle, from that both jets are emanating with similar brightness. This gave rise to the question whether the central radio feature is the center of the AGN. To check this assumption, I analyzed 29 VLBI-observations at 22GHz and 43GHz carried out between March 2005 and April 2009. Two attempts were made to test whether the central feature is the center of the source. The technique of phase-referencing recovers the relative position of VLBI observations to align the maps. A kinematic study was performed to track the kinematic center of the jets. The proper motions for both jets were derived to μ = 1.12 ± 0.46 mas yr−1 for the eastern jet and μ = 1.86±0.61 mas yr−1 for the western jet, leading to apparent speeds of β = 0.34±0.14 and β = 0.56±0.18, respectively. A detailed analysis of the morphology and flux evolution revealed an asymmetry in the two-sided jet system. Measurements of the brightness temperature gradient and opening angle of the jets support these assumptions and show distinctions from the standard model describing a conical jet. In contrast to previous studies of NGC1052, which identified the eastern jet to be approaching and the western jet to be receding, in this work the western jet was proved is the brighter one. In 2006 the jet-system was very symmetric. Starting in 2007 the morphology of the source showed a significant asymmetry, which is seen in the flux ratio between western and eastern jet, too. It rises from around 1 in 2006 to a mean value of 1.7 from 2007 on. There are two possible reasons for this asymmetry: a change of the inclination angle of the jets to the line of sight or an intrinsic asymmetry. Assuming initial symmetric jet parameters, same brightness and velocity for both jets, an estimate on the inclination angle for 2006, and 2007 to 2009 was derived. Within 1σ Gaussian error of the flux density ratios and velocities, the angle to the line of sight has to change from the lowest possible value during 2006 of 84 ◦ to the highest possible value after 2006 of 80 ◦ to explain the results from my analysis. An asymmetry in the jets is more likely than the change of angle to the line of sight, since the morphology, the flux density, and brightness temperature studies reveal an asymmetry in the twin-jet. To explain and initial asymmetry the intrinsic assumptions could be wrong: the velocities and/or the flux densities are not initially the same for both jets. There could be differences in the jet-production for the western and eastern jet, for example resulting from an asymmetric magnetic field or changing particle densities. It is possible that there is an external distorting medium, that has more impact on one of the jets than on the other. To verify the reason for the observed asymmetry more studies have to be conducted, testing the magnetic field, and material producing or distorting the jets.