Dynamical modelling of brightest cluster galaxies: constraints on the IMF

Abstract

We study the stellar and dynamical masses, as well as the stellar populations, of brightest cluster galaxies (BCGs) located in 32 massive clusters, and for a sub-sample of these use the results to place constraints on the Initial Mass Function (IMF). We measure the spatially-resolved stellar population properties of the BCGs, such as recent star formation episodes, and use it to predict their stellar mass-to-light ratios (ϒ*POP). We find that ∼60 per cent of the BCGs have constant ϒ*POP over the radial range (<15 kpc). We also use the stellar and dynamical mass profiles to derive the stellar mass-to-light ratio from dynamics (ϒ*DYN, see Loubser, these proceedings). We directly compare ϒ*POP with ϒ*DYN, and find that for most BCGs, a Salpeter IMF is needed to explain their properties, but we also find a small subset of BCGs for which a Kroupa-like IMF is needed to explain their properties