Comparison of Dark Matter Proportions Across Types of Spiral Galaxies

Authors: Elliott Williams and Amy Lovell

A large obstacle on the path to better understanding the evolution of the Universe is knowing the extent to which “nature” and “nurture” affect structures in our Universe. Recent studies have observed that many galactic properties such as luminosity and morphology are dependent on their environment and in particular, their halos, from the galactic cluster scale down to galaxy groups. In this study, we investigate the relationship between dark matter (as a fraction of the total mass of the galaxy) and morphology of individual galaxies to determine if a similar relationship between galaxies and their environment exists at this scale. Our approach differs in the sense that we look at the proportion rather than the actual value of the characteristic we are studying to control for the size of the galaxies. We select the sample from Sa, Sb, and Sc type galaxies, where the spiral arms of Sa galaxies are the tightest and those of Sb, Sc are increasingly more unwound. While unable to statistically prove due to the sample size, an increasing trend in the dark matter fractions was observed between Sa and Sb type galaxies apart from NGC 4594. Little to no trend was discernable in dark matter between Sb and Sc type galaxies. We suggest a larger sample size and controlling for the environment in future experiments.