Dark matter halo properties of nearby, late-type galaxies

With the advent of detailed simulations of galaxy formation in a CDM universe, specific predictions are being made on the structure of dark matter halos (DMHs) on galaxy scales. However most DMHs of low surface brightness and dwarf irregular galaxies show some level of disagreement with the predictions. To better test these models, I have embarked on a study of 20 nearby, late-type galaxies, carefully chosen to provide the most consistent tests of model predictions. I have obtained deep broad band BVR and narrow band Halpha imaging of each to better constrain the luminous, baryonic component in these galaxies. To constrain the core kinematics of these systems, I have obtained deep, long-slit spectroscopy observations around the wavelength of Halpha. Using new VLA and WSRT full synthesis HI observations for a subsample of galaxies, I have determined extended rotation curves and HI masses. After accounting for the baryonic mass, I modelled the dark matter contribution using the Psuedo-isothermal, Navarro-Frenk-White or Burkert density profile.; Most of the galaxies modelled were better fit by a Pseudo-isothermal DMH as determined by comparing the c2red which were derived from the overall rotation curve fits. Only one galaxy was better fit by a Navarro-Frenk-White DMH. I also compared the circular velocity residuals as a function of radius for each DMH profile. As before, the Puedo-isothermal DMH model yielded the smallest residuals for the same six galaxies referred to above.; I have also presented the DMH density profiles inverted from their Dark Matter rotation curves. Out of seven galaxies, four have profiles with obvious constant density cores. Only one galaxy had a steep DMH density profile with a measured inner power law slope of -1.2, which is consistent with that predicted from numerical simulations. I compared these data with a sample of similarly determined density profiles from the literature, and I found the range and distribution of measured inner slopes consistent. I merged the samples and determined there were no trends in the measured inner power law slopes with absolute magnitude or central surface brightness.