Radio continuum jet in NGC 7479

Creators: Laine, Seppo; Beck, Rainer

Abstract

The barred galaxy NGC 7479 hosts a remarkable jetlike radio continuum feature: bright, 12 kpc long in projection, and hosting an aligned magnetic field. The degree of polarization is 6%-8% along the jet and remarkably constant, which is consistent with helical field models. The radio brightness of the jet suggests strong interaction with the ISM and hence a location near the disk plane. We observed NGC 7479 at four wavelengths with the VLA and Effelsberg radio telescopes. The equipartition strength is 35-40 μG for the total and ≥10 μG for the ordered magnetic field in the jet. The jet acts as a bright, polarized background. Faraday rotation between 3.5 and 6 cm and depolarization between 6 and 22 cm can be explained by magnetoionic gas in front of the jet, with thermal electron densities of ~0.06 cm^−3 in the bar and ~0.03 cm^−3 outside the bar. The regular magnetic field along the bar points toward the nucleus on both sides. The regular field in the disk reveals multiple reversals, probably consisting of field loops stretched by a shearing gas flow in the bar. The projection of the jet bending in the sky plane is in the sense opposite to that of the underlying stellar and gaseous spiral structure. The bending in 3D is most easily explained as a precessing jet, with an age less than 10^6 yr. Our observations are consistent with very recent triggering, possibly by a minor merger. NGC 7479 provides a unique opportunity to study interaction-triggered 15 kpc scale radio jets within a spiral galaxy.

Additional Information

© 2008 The American Astronomical Society. Received 2007 June 20; accepted 2007 September 26. We are grateful to Vladimir Shoutenkov for help with the data reduction and to Matthias Ehle for providing the X-ray image and for model fitting of the X-ray data. We thank Marita Krause for a critical reading of the manuscript and many useful comments on an earlier version of this paper. We thank Max Camenzind, Christian Kaiser, and Robert Laing for very useful discussions on jet triggering mechanisms and Bruce Elmegreen, Arieh Konigl, and Tim Heckman for enlightening discussions on the jet feature. We thank the anonymous referee for many useful comments. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Effelsberg 100 m telescope is operated by the Max-Planck-Institut fur Radioastronomie in Bonn on behalf of the Max-Planck-Gesellschaft (MPG). This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

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