# The local spiral arm in the LAMOST-Gaia common stars?

## TL;DR

This study uses LAMOST-Gaia data to analyze the velocity field of young stars near the local spiral arm, revealing their movement patterns and suggesting a connection to a density wave, with implications for spiral arm formation.

## Contribution

It provides new insights into the velocity behavior of young stars near the local arm and links their motion to a density wave, offering evidence for spiral arm formation mechanisms.

## Key findings

- Young stars move along Y with faster azimuthal velocity on the trailing side of the local arm.
- Residual velocity field shows inward motion of young stars with v_R of -5 to -3 km/s.
- Velocity divergence suggests young stars are associated with a nearby density wave.

## Abstract

Using the LAMOST-Gaia common stars, we demonstrate that the in-plane velocity field for the nearby young stars are significantly different from that for the old ones. For the young stars, the probably perturbed velocities similar to the old population are mostly removed from the velocity maps in the $X$--$Y$ plane. The residual velocity field shows that the young stars consistently move along $Y$ with faster $v_\phi$ at the trailing side of the local arm, while at the leading side, they move slower in azimuth direction. At both sides, the young stars averagely move inward with $v_R$ of $-5\sim-3$ km s$^{-1}$. The divergence of the velocity in $Y$ direction implies that the young stars are associated with a density wave nearby the local arm. We therefore suggest that the young stars may reflect the formation of the local spiral arm by correlating themselves with a density wave. The range of the age for the young stars is around 2 Gyr, which is sensible since the transient spiral arm can sustain that long. We also point out that alternative explanations of the peculiar velocity field for the young population cannot be ruled out only from this observed data.