The "Taffy" Galaxies UGC 12914/5

May 1993 • 1993AJ....105.1730C

Authors • Condon, J. J. • Helou, G. • Sanders, D. B. • Soifer, B. T.

Abstract • The interacting spiral galaxies UGC 12914 and UGC 12915 are joined by a radio continuum bridge whose brightness contours look like stretching strands of taffy as these two galaxies separate following a nearly head- on collision. We propose that the bridge cosmic rays, magnetic fields, and H I gas were stripped from the interpenetrating stellar disks and trace their post-collision orbits. Spectral steepening caused by synchrotron and inverse-Compton losses indicates that the collision occurred ~2 X 10^7^ years ago. New H I maps suggest that the UGC 12914/5 orbit lies nearly in the plane of the sky, and the total masses of UGC 12914 and UGC 12915 estimated from their H I rotation curves also indicate that about 2 X 10^7^ years have passed since the collision if the orbits are nearly parabolic. The disks of UGC 12914/5 obey the standard far-infrared (FIR)/radio correlation, but synchrotron emission from relativistic electrons trapped in the bridge nearly doubles the total radio luminosity of the UGC 12914/5 system. Consequently UGC 12914/5 has a lower FIR/radio ratio than all 258 IRAS Bright Galaxy Sample galaxies thought not to contain a Seyfert nucleus. Apparently the relativistic electrons that normally would have escaped silently into intergalactic space continue to radiate in the bridge magnetic field. We conclude that escape losses cannot be neglected in models explaining the FIR/radio correlation; isolated disk galaxies are not good "calorimeters."

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