Structure and Kinematics of the Milky Way through A stars

Abstract

In the context of the Gaia era, the analysis of the structure and the kinematics of the Milky Way is an ongoing active field of research. Despite A-type stars have a relatively high intrinsic brightness and are moderately numerous as well as kinetically cold, they have been scarcely used as tracers of Galactic properties. This work opens a new window by studying a sample of A-type stars selected using the IGAPS photometric survey. It covers the Galactic plane within 30 ° ≤ l ≤ 215 ° and |b| ≤ 5 ° up to magnitude r ≤ 19 mag with around 3.5 million sources. Gaia EDR3 astrometry and proper motions, together with Gaia DR3 line-of-sight velocities, are used to analyse large-scale features of the Galactic disc. This sample allows to unveil structure and kinematic properties of the Milky Way disc at inter-mediate stellar ages. This includes a study of the obtained density distributions completeness, and a comparison between the b < 0° and b > 0° regions. Furthermore, the sample shows clear evidences of the Galactic warp in its vertical kinematics. Possible biases caused by interstellar extinction or by the usage of some kinematic estimators are examined to verify the results. The last goal of this study is to demonstrate the high potential of A-type stars as Galactic-scale tracers. They can be used to fill the age gap between the youngest OB stars and the old red giants, allowing to expand our knowledge about the evolution of the Galaxy.