The Formation of Disks in Elliptical Galaxies

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Abstract
We investigate detailed kinematical properties of simulated collisionless merger remnants of disk galaxies with mass ratios of 1 : 1 and 3 : 1. The simulations are performed by direct summation using the new special hardware device GRAPE-5. In agreement with observations, the shape of the line-of-sight velocity distribution (LOSVD) is Gaussian with small deviations. For most cases, we find that the retrograde wings of the LOSVD are steeper than the prograde ones. This is in contradiction with observations that show broad retrograde and steep prograde wings. This serious problem in the collisionless formation scenario of massive elliptical galaxies can be solved if all rotating elliptical galaxies, even boxy ones, contain an additional stellar disk component of approximately 15% of the total stellar mass and a scale length of order the effective radius of the spheroid. We propose that the progenitor galaxies of massive elliptical galaxies must have contained a significant amount of gas that did not condense into stars during the merger process itself but formed an extended gaseous disk before the star formation epoch. The heating source that prevented the gas from forming stars early and the origin of the large specific angular momentum required for the gas component to form an extended disk are still unsolved problems.

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