High dynamic range VLBI observations of NGC 6251

Details High dynamic range VLBI observations of NGC 6251 High dynamic range VLBI observations of NGC 6251

Jun 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...305..684j&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 305, June 15, 1986, p. 684-697.

Astronomy and Astrophysics

Astronomy

45

Galactic Nuclei, Radio Jets (Astronomy), Radio Sources (Astronomy), Very Long Base Interferometry, X Ray Astronomy, Circular Polarization, Data Reduction, Doppler Effect, Signal To Noise Ratios, Thermal Noise

Scientific paper

The large radio galaxy NGC 6251 has been observed with an 11-telescope VLBI array, including the full VLA, at 18 cm. High-dynamic-range maps of both the VLBI-scale and VLA-scale radio structure from these observations, as well as hybrid maps from earlier VLBI experiments at 6 and 13 cm, are presented. The 18-cm VLBI hybrid map has an unusually high dynamic range of about 300 to 1 (ratio of the peak brightness to five times the rms noise level) and is limited by thermal noise rather than calibration errors. A lower limit of 80 to 1 for the ratio of jet/counterjet brightness at parsec scales can be set. This is the strongest such limit produced by VLBI observations of any source to date. If the absence of a detectable counterjet is caused by relativistic beaming, then the jet must be aligned within 45 deg of the line of sight. The VLA map shows a complex structure along the previously detected kiloparsec-scale counterjet. The physical conditions in the inner few parsecs of the NGC 6251 jet and their relation to the conditions in the extraordinarily long and well collimated kiloparsec-scale jets are discussed, and it is shown that both small-scale and large-scale morphology can be explained in terms of a simple model and relativistic beaming.

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