Multifrequency Observations of the Double-Nucleus Galaxy Markarian 266: Enhanced Synchrotron Emission Induced by a Merger

October 1988 • 1988ApJ...333..168M

Authors • Mazzarella, Joseph M. • Gaume, Ralph A. • Aller, Hugh D. • Hughes, Philip A.

Abstract • Optical CCD images and radio aperture-synthesis observations are presented for the double-nucleus galaxy Markarian 266 (NGC 5256 = I Zw 67). Although the galaxy appears optically as a disturbed system containing two active nuclei separated by 10", multifrequency radio synthesis images with a resolution of half-power beamwidth (HPBW) = 2" reveal the presence of three separate nonthermal continuum sources. Two of the radio components coincide with optical Seyfert 2 and low-ionization nuclear emission-line region (Liner) nuclei, while the third source lies between the optical nuclei. No optical counterpart to the peak in the central radio component is apparent in broad-band or Hα images. The peculiar optical morphology and far-infrared properties as measured by IRAS indicate that Mrk 266 is an ongoing interaction/merger between two previously separate galaxies. A high-resolution 6 cm synthesis image (HPBW = 0.4" x 0.3") reveals double structure in the central radio component, and a "linear" morphology in the SW component which is similar to that found in many isolated Seyfert nuclei. We propose that the enhanced radio emission between the nuclei of Mrk 266 is produced by synchrotron emission stimulated by the collision of two galaxies. Shocks induced by the collision and possible ongoing merger of two disk galaxies may accelerate electrons and locally enhance the magnetic field in the region between the nuclei where compression and shocking is most intense. A detailed application of Bell's cosmic-ray acceleration mechanism, assuming equipartition of energy to derive the magnetic field and electron density, successfully explains the power and spectrum of the radio source located between the nuclei of Mrk 266. A more general implication is that shock-induced synchrotron emission may be a primary mechanism responsible for findings which indicate that close galaxy pairs and mergers are more likely to be radio-loud than galaxies in other samples.

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Joe Mazzarella

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