VLBI and total flux density investigations of the structure of active galactic nuclei

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Doctoral thesis (article-based)
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36, [75]
Metsähovi publications in radio science, 42
This doctoral thesis studies the structure of active galactic nuclei (AGN) using very long baseline interferometry (VLBI) at high radio frequencies (22 - 86 GHz). The VLBI observations are complemented using information from total flux density (TFD) observations at the corresponding frequencies and the TFD variations are compared to the structure changes seen in the VLBI images. The basis of this work is the data from the three epoch VLBI monitoring project, which produced 45 images and parameters of 15 extragalactic sources at 22 GHz. The maximum intrinsic brightness temperature for synchrotron sources is assumed to be limited by the inverse Compton catastrophe to ≅ 1012 K. We have presented two new methods to estimate this limit using total flux density observations, synchrotron-Self-Compton X-ray fluxes and shock parameters from VLBI observations. Using several data sets, we find that both methods yield a value of ≤ 1011 K, which is consistent with the equipartition limit of 1010 - 1011 K. We have developed a new method for estimating the geometry of the Universe using the linear sizes of shocks in AGN jets. The angular sizes of the shocks from VLBI observations are normalized using intrinsic diameter estimates from TFD observations. Using a very small set of test data, we verify that the accuracy of the derived values compare favourably with traditional methods using much larger samples. A clear connection between radio and gamma-ray flares and VLBI component ejections was found. Furthermore, it was shown that the origin of the gamma-ray flares is in the shocks and that they can not be produced close to the core of the AGN. A helical structure was found in the jet of CTA 102, a High Polarised Quasar (HPQ). The apparent proper motions in the jet varied from 4.2 to 13.8 times the speed of the light. This work combined the work of several years of observation, covering wavelengths from 1.3 to 12 mm and angular resolutions from 50 to 500 microarcseconds. The first 2mm VLBI experiment between Pico Veleta and Metsähovi was performed and correlation fringes were detected on a baseline of 1.55 billion wavelengths. The success of this experiment shows that VLBI observations are possible at very high frequencies leading to very high resolution and enabling to produce images of the fine structure of the cores of the AGN.
cosmology:observations, active galaxies, galaxies:jets, interferometry, VLBI, radiation mechanisms
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  • Lähteenmäki, A., Valtaoja, E., Wiik, K., 1999, Total flux density variations in extragalactic radio sources. II. Determining the limiting brightness temperature for synchrotron sources, The Astrophysical Journal, 511, 112. [article1.pdf] © 1999 American Astronomical Society and authors. By permission.
  • Wiik, K., Valtaoja, E., 2001, The geometry of the universe from high resolution VLBI data of AGN shocks, Astronomy & Astrophysics, 366, 1061. [article2.pdf] © 2001 Astronomy & Astrophysics. By permission.
  • Wiik, K., Valtaoja, E., Leppänen, K., 2001, VLBI monitoring of a sample of 15 AGN at 22 GHz. I. Data, Astronomy & Astrophysics, 380, 72. [article3.pdf] © 2001 Astronomy & Astrophysics. By permission.
  • Valtaoja, E., Savolainen, T., Wiik, K., Lähteenmäki, A., 2002, Millimetre Continuum Variations, VLBI Structure, and Gamma-rays: Investigating Shocked Jet Physics, Publications of the Astronomical Society of Australia, 19, 117. [article4.pdf] © 2002 CSIRO PUBLISHING. By permission.
  • Greve, A., Könönen, P., Graham, D. A., Wiik, K., Krichbaum, T. P., Conway, J., Rantakyrö, F., Urpo, S., Grewing, M., Booth, R. S., John, D., Navarro, S., Mujunen, A., Ritakari, J., Peltonen, J., Sjöman, P., Berton, M., 2002, 147 GHz VLBI Observations: Detection of 3C 273 and 3C 279 on the 3100 km Baseline Metsähovi - Pico Veleta, Astronomy & Astrophysics, 390, L19. [article5.pdf] © 2002 Astronomy & Astrophysics. By permission.
  • Savolainen, T., Wiik, K., Valtaoja, E., Jorstad, S. G., Marscher, A. P., 2002, Connections Between Millimeter Continuum Variations and VLBI Structure in 27 AGN, Astronomy & Astrophysics (in press). [article6.pdf] © 2002 Astronomy & Astrophysics. By permission.
  • Rantakyrö, F. T., Wiik, K., Tornikoski, M., Valtaoja, E., Bååth, L. B., 2002, Multifrequency Interferometer and Radio Continuum Monitoring Observations of CTA 102, Helsinki University of Technology, Metsähovi Publications on Radio Science HUT-MET-37; submitted to Astronomy & Astrophysics. [article7.pdf] © 2002 Astronomy & Astrophysics. By permission.
  • Wiik, K., Valtaoja, E., Lähteenmäki, A., 2000, Comparison of Total Flux and VLBI Properties of a Sample of Fifteen AGN at 22 GHz, in Astrophysical Phenomena Revealed by Space VLBI, Proceedings of the VSOP Symposium Eds.: H. Hirabayashi, P.G. Edwards, and D.W. Murphy, Published by the Institute of Space and Astronautical Science, Kanagawa, Japan, 321.
  • Valtaoja E, Wiik K, 1999, AGN shocks as cosmological standard rods, Second Millimeter-VLBI Science Workshop, IRAM Granada, Spain, 21.
  • Wiik, K., Valtaoja, E., 1998, Comparison of Total Flux and VLBI Properties of a Sample of 15 AGN at 22 GHz, ASP Conference Series, 1998, Volume 144, IAU Colloquium 164, eds. J.A. Zensus, G.B. Taylor, & J.M. Wrobel, 144, 151.
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