Diagonal Ridge Pattern of Different Age Populations Found in Gaia-DR2 with LAMOST Main-sequence Turnoff and OB-type Stars

Abstract

We revisit the diagonal ridge feature (diagonal distributions in the R , v ϕ plane) found in Gaia and present a timing analysis for it between Galactocentric distances of R  = 7.5 and 12 kpc, using main-sequence turnoff and OB stars selected from the LAMOST Galactic spectroscopic surveys. We recover the ridge pattern in the R – v ϕ plane color coded by mean radial velocity and find that this feature is presented from very young (OB stars, few hundred megayears) to very old populations ( τ  = 9–14 Gyr). Meanwhile, some ridge features are also revealed in the metallicity [Fe/H], [ α /Fe], and v z distributions. In the L Z , v ϕ plane, one of the ridge patterns, with constant angular momentum per unit mass, shows variations with different age populations compared. However, the remaining two are relatively stable, implying there might be two kinds of ridge patterns with different dynamical origins and evolutions.