We revisit the diagonal ridge feature (diagonal distributions in the $R, v_{\phi}$ plane) found in $Gaia$ and present timing analysis for it between Galactocentric distances of $R=7.5$ and 12 \,kpc, using Main-Sequence-Turn-Off and OB stars selected from the LAMOST Galactic spectroscopic surveys. We recover the ridge pattern in the $R$--$v_{\phi}$ plane color coded by mean radial velocity and find this feature is presented from very young (OB stars, few hundred \,Myr) to very old populations ($\tau$ = 9$-$14 \,Gyr). Meanwhile, some ridge features are also revealed in the metallicity [Fe/H], [$\alpha$/Fe] and $v_{z}$ distributions. In the $L_{Z}, v_{\phi}$ plane, one of the ridge patterns, with constant angular momentum per unit mass, shows variations with different age populations compared. However, the remaining two ones are relatively stable, implying there might have two kinds of ridge patterns with different dynamical origins and evolution.

中文翻译：

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在具有LAMOST主序关闭和OB型恒星的Gaia-DR2中发现的不同年龄人口的对角脊模式

我们重新审视了在 $Gaia$ 中发现的对角脊特征（$R, v_{\phi}$ 平面中的对角线分布），并使​​用 Main 在 Gaiacentric 距离 $R=7.5$ 和 12 \,kpc 之间对其进行时序分析-从 LAMOST 银河光谱调查中选择的序列关闭和 OB 星。我们恢复了 $R$--$v_{\phi}$ 平面中由平均径向速度颜色编码的脊图案，发现这个特征从非常年轻的（OB 星，几百 \,Myr）到非常老的种群（ $\tau$ = 9$-$14 \,Gyr)。同时，在金属丰度 [Fe/H]、[$\alpha$/Fe] 和 $v_{z}$ 分布中也揭示了一些脊特征。在 $L_{Z}, v_{\phi}$ 平面中，脊模式之一，每单位质量具有恒定的角动量，比较不同年龄人群的变化。不过剩下的两个比较稳定，