Colliding and merging galaxies. I - Evidence for the recent merging of two disk galaxies in NGC 7252

Results from a photographic, spectroscopic, and photometric study of the 'Atoms-for-Peace' galaxy are presented. The observations reveal that NGC 7252 possesses a single nucleus, a nearly round main body marked by delicate ripples, faint surrounding loops, and two slender tails that project to 80 kpc and 130 kpc from the center. The principal body itself shows a spectrum indicative of young A stars and contains a small central disk of ionized gas. The disk rotates with v sin i approximately equal to 80-100 km/s around a well-defined axis, whereas the gas immediately beyond it follows a totally different motion pattern. Five characteristics taken together indicate a recent merger of two similarly massive disk galaxies: the two tails, the unusual isolation opposite tail motions, the single nucleus and body, and the two surviving motion systems of the gas.