| Abstract : | The interstellar medium (ISM) of a spiral galaxy is very much dynamically active and forms the playground for star formation. Various factors like large-scale distribution in dark matter halo, differential galactic rotation, interaction with satellite galaxies, stellar feedback etc give rise to different density and velocity structures in the ISM. Turbulence in the ISM gives rise to scale-invariant random structures, which eventually play an active role in regulating the star formation, by enhancing the gravitational clustering and adding to thermal pressure gradients. Through numerous multiwavelength observations, these structures are traced and some of their statistical properties like the density power spectrum, velocity dispersion and radial variation are well established. However, the generation mechanisms of these structures are yet to be understood. In this thesis, we attempt to probe these structures and their dynamics in nearby spiral galaxies. We enhance the measurement of HI column density power spectrum and for the first time measure the line of sight velocity power spectrum for external spiral galaxies. These measurements let us infer on the generating mechanism of coherent structures at ~10 kpc scales and comment on the energy they cascade to the star formation scales announcing their effect. A seemingly different but still interesting dynamical effect in the galaxy’s disc is the bending waves. These arise due to interaction with satellite galaxies, and tidal effects amongst many others. Observationally the bending waves are traced as corrugation in edge-on discs for density and in the face on stellar discs for velocity mostly in optical or infrared. The second part of the thesis discusses the investigation of large-scale corrugation in gas density and velocity using 21-cm observations of several spiral galaxies. Here we find that the disk is vertically perturbed at the stellar extent, where lower multipole bending waves are more frequent. |
