MSc defense Stephen Halberg Hansen

Title: Initial Mass Function Universality

Vejleder: Jens Hjorth

Abstract
The Initial Mass Function (IMF) describes the distribution of a population of stars according to their mass. There exist several different IMFs today, with each having their unique shape. For each IMF, a Star Formation Rate (SFR) can be calculated, with it being different for each IMF. Today, one can convert between the SFR from different IMFs, by using constants, multiplied it to a SFR from one IMF to get a SFR from another IMF. It is not known however, if these constants change as either the parameters of the IMFs are changed or the parameters of the stellar population are changed, such as the age of it, or the parameters defining the calculation of the SFR. In this thesis, I calculate the SFR for different IMFs, the ratios between them, and how the ratios change as a fuction of several interesting parameters, using spectra from Stellar Population Synthesis (SPS) models, which allows one to create spectra from stellar population with a given IMF, metallicity, age of the stellar population, and such.  I also calculate several interesting variables and the ratios between them using the IMFs themselves only, without using SPS models. I find that the SFR ratios between different IMFs are dependent on parameters describing the IMFs and parameters describing the stellar population, meaning that the constants used for conversion between SFR from different IMFs are dependent on these. I also find that the variables derived from IMFs themselves are also dependent on the parameters describing the IMFs. With the results from here, I create a universal tool for conversion between different IMFs as a function of these parameters, creating an "Initial Mass Function Universality" for the IMFs used here, and also explain how the stellar population will evolve as the IMF parameters are changed.