Constraining the Milky Way assembly history with Galactic Archaeology

Abstract

The aim of Galactic Archaeology is to recover the evolutionary history of the Milky Way from its present day kinematical and chemical state. Because stars move away from their birth sites, the current dynamical information alone is not sufficient for this task. The chemical composition of stellar atmospheres, on the other hand, is largely preserved over the stellar lifetime and, together with accurate ages, can be used to recover the birthplaces of stars currently found at the same Galactic radius. In addition to the availability of large stellar samples with accurate 6D kinematics and chemical abundance measurements, this requires detailed modeling with both dynamical and chemical evolution taken into account. An important first step is to understand the variety of dynamical processes that can take place in the Milky Way, including the perturbative effects of both internal (bar and spiral structure) and external (infalling satellites) agents. We discuss here (1) how to constrain the Galactic bar, spiral structure, and merging satellites by their effect on the local and global disc phase-space, (2) the effect of multiple patterns on the disc dynamics, and (3) the importance of radial migration and merger perturbations for the formation of the Galactic thick disc. Finally, we discuss the construction of Milky Way chemo-dynamical models and relate to observations.

Stellar metallicity gradients of the Milky Way disc from LAMOST

“…The flattening trend of metallicity gradients with R and Z for the younger, mono-age populations are probably consequences of stellar migration and disc flaring (Minchev et al 2014, Kawata et al 2017. A flaring phenomenon for almost all mono-age disc populations have been predicted by simulations (Minchev 2016), and also been observed recently (Xiang et al 2018). Nevertheless, mechanisms cause the reverse trend of metallicity gradient as a function of age need to be further understood.…”

Fundamental relations for the velocity dispersion of stars in the Milky Way

“…Because the heating rate is higher in the inner regions than in the outer regions, one has to take migration into account when modelling the AVR at a given location. However, in a comprehensive review of stellar migration, Minchev (2016) argues that migration, on average, generally does not lead to disc heating.…”

Yule-Simpson’s paradox in Galactic Archaeology

“…Galactic Archaeologists use the observed stellar kinematics, chemical abundances, and derived ages as fossil records to recover the chemo-dynamical history of the Milky Way (Freeman & Bland-Hawthorn 2002;Bland-Hawthorn et al 2010;Rix & Bovy 2013;Binney 2013;Minchev 2016;Hogg et al 2016). Age information is by far the hardest one to obtain, yet extremely important to break degeneracies among different chemical evolution models (Miglio et al 2017).…”