Astron. Astrophys. 364, 391-408 (2000)

86 GHz VLBI survey of compact radio sources ^*

A.P. Lobanov ¹, T.P. Krichbaum ¹, D.A. Graham ¹, A. Witzel ¹, A. Kraus ¹, J.A. Zensus ^1,3, S. Britzen ^1,4, A. Greve ² and M. Grewing <sup>2

1</sup> Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² IRAM, Grenoble, 300 Rue de la Piscine, 38460 St. Martin d'Héres, France
³ National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA
⁴ Present address: JIVE, Postbus 2, Dwingeloo AA 2990, The Netherlands

Received 17 September 1999 / Accepted 12 October 2000

Abstract

We present results from 86 GHz VLBI ¹ observations of 28 compact radio sources made in April 1993. All but two of the observed objects are active galactic nuclei. The remaining two objects are the galactic center Sgr A^* and the X-ray binary star Cygnus X-3. Of the observed sources, 26 have yielded fringe detections. We present correlated flux densities, estimate the maximum observed brightness temperatures, and provide single Gaussian component model fits. Out of the 17 sources with good uv -coverages, 3 are without detectable structural details (0642+449, 0716+714, and Cygnus A), 3 have little closure phase information (4C67.05, 1823+568, and 1928+738), and the remaining 11 have been imaged. We study the brightness temperatures, , of the observed sources, and apply a basic population model with a single value of the intrinsic brightness temperature, , in order to reproduce the observed distribution of . Our data are consistent with a population of sources that have K in the jets, and - K in the VLBI cores. The observed are also correlated with the apparent speeds measured in the jets. For comparison, we apply the same population scenario to a larger sample of 132 AGN observed with VLBI at 15 GHz, and show that the distribution of brightness temperatures from that sample is consistent with the intrinsic brightness temperature of K. The observed decrease of along the jets can be reproduced by adiabatic losses in relativistic shocks embedded in the jet.

Key words: galaxies: active galaxies: jets galaxies: nuclei galaxies: quasars: general radio continuum: galaxies

* Figs. 25 to 30 are only available here in electronic form with the On-line publication. Table 1, Table 4, and Table 5 are also available at the CDS via anonymous ftp to cdsarc.u.strasbg.fr (130.79.128.5) or via http://cdsweb.u.strasbg.fr/cgi-bin/qcat?J/A+A/364/391 .

Send offprint requests to: A.P. Lobanov

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Contents

• 1. Introduction
• 2. Observations
  • 2.1. Amplitude calibration
  • 2.2. Structure analysis
    • 2.2.1. Single-component models
    • 2.2.2. Multi-component models
    • 2.2.3. Hybrid images
• 3. Results
  • 3.1. Images and notes on individual sources
• 4. Brightness temperature and jet physics
  • 4.1. Population model for the jet brightness temperatures
  • 4.2. Shortcomings of the population model
  • 4.3. Evolution of brightness temperature in the jets
  • 4.4. Brightness temperatures and jet speeds
  • 4.5. VLBI data at lower frequencies
• 5. Summary
• Acknowledgements
• Appendices
  • A: brightness temperature distribution
  • B: the - correlation
  • C: visibility distributions
• References

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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