Statistical Properties of Collisionless Equal‐ and Unequal‐Mass Merger Remnants of Disk Galaxies

We perform a large parameter survey of 112 collisionless N-body simulationsof binary mergers of disk-galaxies with mass ratios of 1:1, 2:1, 3:1, and 4:1using the special purpose hardware GRAPE. The basic properties of the remnantscorrelate with the mass ratio of the progenitor disks. We find that about 80%of the equal-mass merger simulations lead to slowly rotating remnants withsignificant minor-axis rotation. One half of all projected 1:1 remnants showsboxy and the other half shows disky isophotes. Remnants with mass ratios of 3:1and 4:1 all rotate fast and show a small amount of minor-axis rotation. About90% of the projected 3:1 and 4:1 remnants show disky isophotes. 2:1 remnantsshow intermediate properties. Projection effects lead to a large spread in thedata in good agreement with observations. They do not change the fundamentalkinematical differences between equal-mass and unequal-mass merger remnants.The results of this study weaken the disk merger scenario as the possibleformation mechanism of massive boxy giant ellipticals. In general, theproperties of equal-mass (and 2:1) merger remnants are consistent with theobserved population of giant ellipticals in the intermediate mass regimebetween low mass fast rotating disky and bright massive boxy giant ellipticals.3:1 and 4:1 merger remnants, however, are in very good agreement with the classof low luminosity, fast rotating giant elliptical galaxies. Binary mergers ofdisk galaxies are therefore still very good candidates for being the mainformation mechanism for intermediate and low mass giant ellipticals. Thehomogeneous class of massive boxy ellipticals most likely formed by a differentprocess.Comment: 35 pages, 16 figures, significantly revised version accepted for publication by Ap