The measurement of stellar masses in
= 0.5 galaxies using the micro-lensing of quasars
Massachusetts Institute of Technology
We measure the stellar mass surface densities of early type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single epoch X-ray snapshots of ten quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter IMF with a low mass cutoff of 0.1 solar masses and treat the zeropoint of the surface mass density as a free parameter. Our method measures the GRAININESS of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.53, with a one sigma confidence range, dominated by small number statistics, of 0.95 < F < 2.5.
Date: Friday, 13 May 2016 Time: 15:30 Where: McGill University McGill Space Institute (3550 University), Conference Room Contact: Robert Rutledge