High Galactic latitude runaway stars as tracers of the spiral arms

Abstract

A direct observation of the spiral structure of the Galaxy is hindered by our position in the middle of the Galactic plane. We propose a method based on the analysis of the birthplaces of high Galactic latitude runaway stars to map the spiral arms and determine their dynamics. As a proof of concept, the method is applied to a local sample of early-type stars and a sample of runaways stars to obtain estimates of the pattern speed (Ωp, local = 20.3 ± 0.5 km s-1 kpc-1 and Ωp, runaway = 21.9 ± 8.6 km s-1 kpc-1) and the spiral arm's phase angle (φlocal = -53.1° ± 3.1° and φrunaway = -63.5° ± 22.5°). We also estimate the performance of this method once the data gathered by Gaia, in particular for runaway stars observed on the other side of the Galaxy, are available