Cake Talk: Chiara Spiniello

Chiara Spiniello, MPA Postdoc Fellow at the Max-Planck-Institut für Astrophysik, Garching

Title: The XLENS Project: Constrain the Initial Mass Function and the Luminous & Dark Matter distribution in massive Early-Type Galaxies


I will introduce present results from The X-Shooter Lens Survey (XLENS). With XLENS we are able to fully separate the stellar from the dark-matter content in the internal region of lens early-type galaxies (ETGs)  to understand their interplay and to probe directly their formation and dynamical evolution. We combine precise strong gravitational lensing and dynamical constraints on the mass distribution with high signal-to-noise spectroscopy in the entire rest-frame visible to the NIR.

First, I will introduce the Survey, focussing on its scientific goals as well as the method and techniques used to study the mass distribution of a sample of very massive lens ETGs, with velocity dispersions greater than 250 km/s and redshift 0.1<z<0.5. I will then show how to constrain the low-mass end of the Initial Mass Function (IMF) directly from galaxy optical spectra using a new set of non-degenerate optical spectroscopic indices which are strong in cool giants and dwarfs and almost absent in main sequence stars (Spiniello et al., 2014, Spiniello et al. 2015a). I will present unambiguous evidence that the low-mass end of the IMF is not universal.  Finally, I will demonstrate that the combination of this SSP modelling with a fully self-consistent  joint lensing+dynamics analysis (Barnabè et al. 2012) allows us to disentangle IMF slope variations from internal dark-matter variations and, for the first time ever, to contemporary put constrains on the IMF cutoff mass (Barnabè et al., 2013, Spiniello et al., 2015c).