# The spiral pattern rotation speed of the Galaxy and the corotation radius with GAIA DR2

## TL;DR

This study uses Gaia DR2 data of young open clusters to measure the spiral arm rotation speed and corotation radius of the Milky Way, finding a pattern speed of about 28.2 km/s/kpc and a corotation radius near the solar orbit.

## Contribution

It provides a new measurement of the Galaxy's spiral pattern speed and corotation radius using a homogeneous dataset of young clusters from Gaia DR2.

## Key findings

- Pattern speed of 28.2 km/s/kpc with 2.1 km/s/kpc uncertainty.
- Corotation radius approximately 8.5 kpc, close to the Sun's orbit.
- No difference in pattern speed among different spiral arms.

## Abstract

In this work we revisit the issue of the rotation speed of the spiral arms and the location of the corotation radius of our Galaxy. This research was performed using homogeneous data set of young open clusters (age < 50 Myr) determined from Gaia DR2 data. The stellar astrometric membership were determined using proper motions and parallaxes, taking into account the full covariance matrix. The distance, age, reddening and metallicity of the clusters were determined by our non subjective multidimensional global optimization tool to fit theoretical isochrones to Gaia DR2 photometric data. The rotation speed of the arms is obtained from the relation between age and angular distance of the birthplace of the clusters to the present-day position of the arms. Using the clusters belonging to the Sagittarius-Carina, Local and Perseus arms, and adopting the Galactic parameters $R_0$ = 8.3 kpc and $V_0$ = 240 km\,s$^{-1}$, we determine a pattern speed of $28.2 \pm 2.1$ km\,s$^{-1}$\,kpc$^{-1}$, with no difference between the arms. This implies that the corotation radius is $R_c = 8.51 \pm 0.64$ kpc, close to the solar Galactic orbit ($R_c/R_0 = 1.02\pm0.07$).