The hight transverse velocity stars in Gaia-LAMOST

Although the stellar halo accounts for just ~1% of the total stellar mass of the Milky Way, their kinematics tell us a lot about the origins and evolution of our Galaxy. It has been shown that the high transverse velocity stars in Gaia DR2 reveal a double sequence in the Hertzsprung-Russell (HR) diagram, indicating a duality in the local halo within 1 kpc. We fit these stars by updating the popular Besancon/Galaxia model, incorporating the latest observational results for the stellar halo. We are able to obtain a good match to the Gaia data and provide new constraints on the properties of the disc and halo. In particular, we show that the canonical thick disc contribution to the high velocity tail is small, but not negligible, and likely has an influence on the red sequence of the HR diagram. Check Amarante+20a for details!

Normalised histogram of the transverse velocity for Gaia data and our model, black and green respectively. Our modelling updates the canonical Galaxia model kinematics and the thick disc and stellar halo fractions.