Event Details

Hunting the Ghosts of Galaxies

In recent decades it has become clear that galaxies form through two distinct processes; the in-situ conversion of gas into stars, and the acquisition of stars originally formed in separate galaxies (ex-situ stars) during galaxy-galaxy interactions and mergers. Modern hydrodynamical simulations of galaxy formation indicate that the ex-situ fraction rises dramatically as a function of galaxy mass (from ~10% of all stars at Milky Way masses to over 90% for the most massive galaxies). Unfortunately, observationally determining the ratio of in-situ to ex-situ stars in galaxies beyond the Milky Way has proven to be extremely difficult.

In this talk I will present a new technique which leverages the power of full-spectral fitting of galaxy spectra and the mass-metallicity relation of galaxies in order to determine the fraction of stars that were accreted by a galaxy. I will compare the observationally measured ex-situ fractions for a sample of early-type galaxies drawn from across the mass-size plane to those predicted by the simulations, demonstrating good agreement, and thereby lending further support to the prediction that at fixed mass, more extended galaxies have accreted a larger fraction of their stars.

If someone from outside of the Astrophysics group would like to join the webinar, please send a request to i.garland@lancaster.ac.uk