Galactic disks, infall, and the global value of Omega

摘要: Stringent limits on the current rate of infall satellite systems onto spiral galaxies are set basis thinness and coldness Galactic disks. For infalling satellites isotropically oriented circular orbits, it is shown that, due to scattering, thermal energy gain disk exceeds loss from dynamical friction by a factor 1.6, with 25 percent deposited in z motion 75 planar motions. It found that no more than 4 mass inside solar radius can have accreted within last 5 billion years, or else its scale Toomre Q-parameter would exceed observed values. In standard cold-dark-matter-dominated models for growth structure Omega sub tot 1, dark matter lumps rises faster t exp 2/3 28 Gyr. proposed heating accounts substantial fraction increase velocity dispersion height age Galaxy.