Two tails in NGC 3656 and the major merger origin of shell and minor-axis dust lane elliptical galaxies

I report on the discovery of two faint (similar to 26.8 R mag arcsec(-2)) tidal tails around the shell elliptical galaxy NGC 3656 (Arp 155). This galaxy had previously been interpreted as a case of accretion, or minor merger. The two tidal tails are inconsistent with a minor merger and point instead to a disk-disk major merger origin. NGC 3656 extends Toomre's merger sequence toward normal elliptical galaxies and hints at a major merger origin for shells and minor-axis dust lanes. A dwarf galaxy lies at the tip of one of the tidal tails. A prominent shell, which shows sharp azimuthal color discontinuities, belongs to a rotating dynamical component with young stars that includes the inner dust lane.