We evaluate the radiation and gravitational forces on dust grains out of the disk for a large sample of spiral galaxies. The main results are a selective expulsion of grains and the presence of equilibrium positions inside the halo, providing a new test for the distribution of dark matter.
It is argued that spiral patterns in galaxies generally are transient features which will decay away in a few dynamical times, only to be replaced by other similarly short-lived waves. The evidence for this point of view is presented and the current state of the theory is discussed. A major consequence of such behaviour is that disc stars are scattered into gradually more eccentric orbits by successive spiral waves. This has two further implications: (a) the velocity dispersion of stellar populations will increase with their ages and (b) persistent spiral structure demands a gas component in the disc that can dissipate some of the random moiton energy. That the theory offers such a matural explanation for these two well established aspects of galactic structure is cited as indirect evidence in its favour.
The evolutionary ayntheaio rnethod is applied to calculate Mgl+MgH λ 5150 and TiO λ 7150 absorption features of integrated spectra and integrated UBV colours of a stellar system. These calculations are used to investigate star formation rate in nuclei of some spiral galaxies. The (IMg, B-V) diagram is shown to be a goo discriminator between metallicity and star formation effects. Star formation rates, metallicities and initial mass function slopes are obtained for the nuclei of 8 spiral galaxies. Star formation rates in nuclei correlate with rotation velocities of galaxies. Dynamical friction of gas clouds system in a galactic stellar disk is the possible cause of that correlation.