We use N-body/hydrodynamic simulations to study the evolution of the spin of a Milky Way-like galaxy through interactions. We perform a controlled experiment of co-planar galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specically, we consider cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with a closest approach distance of about 50 kpc, in prograde or retrograde sense. By examining the time change of the circular velocity of the disk material of the target galaxy from each case, we nd that the target galaxy tends to lose the spin through prograde collisions but hardly through retrograde collisions, regardless of the companion galaxy type. The decrease of the spin results mainly from the de ection of the orbit of the disk material by tidal disruption. Although there is some disk material which gains the circular velocity through hydrodynamic as well as gravitational interactions or by transferring material from the companion galaxy, it turns out that the amount of the material is generally insucient to increase the overall galactic spin under the conditions we set. We nd that the spin angular momentum of the target galaxy disk decreases by 15{20% after a prograde collision. We conclude that the accumulated eects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies.

Introduction
Model Description
Simulation Results
Summary and Discussion
Acknowledgments
Run LLr2
References

• Jeong-Sun Hwang(Department of Physics and Astronomy, Sejong University, Seoul 05006, Korea, Department of Science Education, Gwangju National University of Education, Gwangju 61204, Korea) Corresponding author
• Changbom Park(School of Physics, Korea Institute for Advanced Study, Seoul 02455, Korea)
• Soo-hyeon Nam(Department of Physics, Korea University, Seoul 02841, Korea)
• Haeun Chung(University of Arizona, Steward Observatory, 933 N Cherry Ave., Tucson, AZ 85721, USA)