We are deriving star formation histories (SFH) for the Milky Way disk and halo using the robust technique of color-magnitude diagram (CMD) fitting applied to Gaia DR2 CMDs.

The technique of CMD fitting is a well recognized method that has been used for over 20 years to determine detailed SFH for Local Group galaxies (Gallart et al. 2005; Tolstoy et al. 2009).  However, applying this technique to derive the SFH of populations of Milky Way stars had only been possible within an extremely small volume around the Sun for which distances were obtained by Hipparcos (Hernandez et al. 2000, Bertelli & Nasi 2001, Cignoni et al. 2006) or delivered in Gaia DR1 (Bernard 2018). The accurate distances for large stellar samples provided in Gaia DR2, together with the precise, homogeneous Gaia photometry, is enabling a real breakthrough in this field: this information has allowed us, for the first time, to apply the CMD-fitting technique to the different morphological components of our own Galaxy and therefore to robustly derive their SFHs and age distributions using only the Gaia photometric information of millions of stars. This provides answers to long lasting questions regarding the formation and evolution of the disk and halo components of the Milky Way, for which the determination of stellar ages was necessary.  

See results on

The SFH across the think and thick disk of the Milky Way close to the Sun.

The SFH of the Milky Way halo (accreted Gaia-Enceladus + in-situ halo).