Speaker
Description
Through the survey of Planetary Nebulae (PNe) in M31 with Megacam@CFHT, we identify ~5000 PNe in M31 with ~1200 having spectroscopic observations from Hecospec@MMT (~300 of which also have chemical abundance measurements). We find the kinematically and chemically distinct thin and thick discs of M31, as well as the kinematics of its inner-halo substructures. Of particular note, we find that the [Ar/H] vs [O/Ar] plane for emission line nebulae is analogous to the [Fe/H] vs [α/Fe] plane for stars, and exploration of the M31 PN population in this plane (with GCE models) allowed us to constrain the chemical enrichment and star formation history of the thin and thick disc in M 31 (that contrast that of the MW). Using PNe as chemodynamical probes and from GCE models, we infer that majority of the stellar population in the M31 disc was formed at very early times, and was disrupted by a wet major (mass ratio ~ 1:5) merger ~2.5-4 Gyr ago to form the thick disc while the thin disc was reformed in a burst (including relatively metal-poor gas brought in by the satellite) following the merger. We also obtain important constraints on the properties of the cannibalized satellite.
