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تسجيل مستخدم جديدUnderstanding the velocity distribution of the Galactic Bulge with APOGEE and Gaia
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We revisit the stellar velocity distribution in the Galactic bulge/bar region with APOGEE DR16 and {it Gaia} DR2, focusing in particular on the possible high-velocity (HV) peaks and their physical origin. We fit the velocity distributions with two different models, namely with Gauss-Hermite polynomial and Gaussian mixture model (GMM). The result of the fit using Gauss-Hermite polynomials reveals a positive correlation between the mean velocity ($bar{V}$) and the skewness ($h_{3}$) of the velocity distribution, possibly caused by the Galactic bar. The $n=2$ GMM fitting reveals a symmetric longitudinal trend of $|mu_{2}|$ and $sigma_{2}$ (the mean velocity and the standard deviation of the secondary component), which is inconsistent to the $x_{2}$ orbital family predictions. Cold secondary peaks could be seen at $|l|sim6^circ$. However, with the additional tangential information from {it Gaia}, we find that the HV stars in the bulge show similar patterns in the radial-tangential velocity distribution ($V_{rm R}-V_{rm T}$), regardless of the existence of a distinct cold HV peak. The observed $V_{rm R}-V_{rm T}$ (or $V_{rm GSR}-mu_{l}$) distributions are consistent with the predictions of a simple MW bar model. The chemical abundances and ages inferred from ASPCAP and CANNON suggest that the HV stars in the bulge/bar are generally as old as, if not older than, the other stars in the bulge/bar region.
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