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The measurement of stellar masses in = 0.5 galaxies using the micro-lensing of quasars

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. 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.
Speaker: Paul Schechter, MIT

Thursday, 04/21/16

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Free

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Kavli Institute Astrophysics Colloquium

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