The distribution of mass with spiral galaxies. Unique solutions from gas and stellar kinematics

PhD ceremony: Mr. T.P.K. Martinsson, 16.15 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: The distribution of mass with spiral galaxies. Unique solutions from gas and stellar kinematics

Promotor(s): prof. M.A.W. Verheijen

Faculty: Mathematics and Natural Sciences

This thesis investigates the amount and distribution of dynamically distinct components such as stars, gas, and dark matter, in thirty spiral galaxies similar to our own Milky Way, with direct implications for our general understanding of the formation and evolution of galaxies. With optical and radio spectroscopy, I have measured the total dynamical mass of each galaxy based on the rotation speed of the disk. The total mass of a galaxy's disk component follows from the measured random motions of the stars while the masses of the atomic and molecular gas disks follow directly from their emission in the infrared and radio regions of the electromagnetic spectrum. The mass and distribution of the dark matter is then calculated by considering the difference between the total dynamical mass and the mass of the visible components. Contrary to what is commonly assumed, I have found that dark matter is an important and often dominant mass component even in the most luminous, central regions of spiral galaxies. On average, the visible components of spiral galaxies contribute approximately 30 percent to the total mass within a radius comparable to that of the orbit of the Sun in our Milky Way galaxy; the remaining 70 percent of the mass is dark. This implies that the luminous mass of disk galaxies is approximately three times lower than commonly assumed.