Phd ceremony Ms. C. Spiniello: The initial mass function in early-type galaxies

Phd ceremony: Ms. C. Spiniello. 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The initial mass function in early-type galaxies

Promotor(s): prof. L.V.E. Koopmans, prof. S.C. Trager

Faculty: Mathematics and Natural Sciences

In this thesis we investigated the internal structure and the distribution of dark and luminous matter in the inner region of the most massive systems in the Universe, the early-type galaxies (ETGs), whose formation scenario puts still a big strain on modern cosmology.

Specifically, we focussed on constrain the stellar Initial Mass Function (IMF), its low-mass end slope and cutoff-mass directly from galaxy spectra by combining strong gravitational lensing, stellar kinematics and stellar population analysis. The IMF is the distribution of stellar masses that form in one star-formation event. Hence, since the star’s mass determines its subsequent evolutionary path, all the observable properties of galaxies (i.e., colour and luminosity) are heavily influenced by its IMF and star-formation history. Often unappreciated, the IMF is a fundamental cornerstone in modern astrophysics and cosmology, thus detecting variations in the IMF shape with galaxy properties provides deep insights into the process by which stars form within the Cold Dark Matter framework. Recent observations indicate that the internal dark-matter fraction of ETGs increases rapidly with galaxy mass, although a number of hints for a varying IMF slope have been suggested. With the XLENS we have designed and applied a powerful tool to disentangle between the two scenarios and to constrain the low-mass end and cut-off mass of the IMF directly from galaxy spectra. We have presented here solid spectroscopic evidences that indicate that the low-mass end of the IMF slope steepens with the stellar velocity dispersion of the galaxy.