Impacts of the Local arm on the local circular velocity inferred from the Gaia DR3 young stars in the Milky Way

TL;DR

This study uses Gaia DR3 data and simulations to analyze how the Local arm influences local circular velocity measurements, revealing that the Local arm affects kinematic estimates and suggesting a method to infer the true azimuthally averaged circular velocity.

Contribution

The paper introduces a method to account for the Local arm's impact on circular velocity measurements using Gaia data and simulation comparisons.

Findings

The Local arm influences the kinematics of young stars near the Sun.

The measured local circular velocity is affected by the Local arm's co-rotation resonance.

The azimuthally averaged circular velocity near the Sun is estimated at approximately 234 km/s.

Abstract

A simple one-dimensional axisymmetric disc model is applied to the kinematics of OB stars near the Sun obtained from Gaia DR3 catalogue. The model determines the 'local centrifugal speed' $V_\mathrm{c}(R_{0})$ - defined as the circular velocity in the Galactocentric rest frame, where the star would move in a near-circular orbit if the potential is axisymmetric with the local potential of the Galaxy. We find that the $V_\mathrm{c}(R_{0})$ values and their gradient vary across the selected region of stars within the solar neighbourhood. By comparing with an N-body/hydrodynamic simulation of a Milky Way-like galaxy, we find that the kinematics of the young stars in the solar neighbourhood is affected by the Local arm, which makes it difficult to measure $V_\mathrm{c}(R_{0})$. However, from the resemblance between the observational data and the simulation, we suggest that the known rotational velocity gap between the Coma Bernices and Hyades-Pleiades moving groups could be driven by the co-rotation resonance of the Local arm, which can be used to infer the azimuthally averaged circular velocity. We find that $V_\mathrm{c}(R)$ obtained from the $\mathrm{D}<2$ kpc sample is well matched with this gap at the position of the Local arm. Hence, we argue that our results from the $\mathrm{D}<2$ kpc sample, $V_\mathrm{c}(R_{0})= 233.95\pm2.24$ km $\mathrm{s}^{-1}$, is close to the azimuthally averaged circular velocity rather than the local centrifugal speed, which is influenced by the presence of the Local arm.