A-type stars in the Canada-France Imaging Survey II. Tracing the height of the disc at large distances with Blue Stragglers

TL;DR

This study uses Blue Straggler stars from the CFIS survey to analyze the Milky Way's disc structure, revealing significant flaring at large distances likely caused by dynamical heating from the Sagittarius dwarf galaxy.

Contribution

It provides the first detailed kinematic analysis of Blue Straggler stars to trace the flaring of the Milky Way disc at large radii.

Findings

Detected disc flaring up to 8 kpc at 27 kpc Galactocentric distance.

Strong disc flaring is more consistent with dynamical heating by Sagittarius dwarf galaxy.

Kinematic decomposition distinguishes halo and disc populations.

Abstract

We present the kinematics of Blue Straggler (BS) stars identified in the Canada-France-Imaging-Survey (CFIS), covering 4000 deg$^2$ on the sky in the $u$-band. The BS sample, characterised through CFIS and Pan-STARRS photometry, has been kinematically decomposed into putative halo and disc populations after cross-matching with Gaia astrometry and SDSS/SEGUE/LAMOST spectroscopy. This decomposition clearly reveals the strong flaring of the outer Milky Way disc. In particular, we show that we can detect this flaring up to a vertical height of $|Z| \simeq 8$ kpc at a Galactocentric distance of $R\sim $27 kpc. While some small level of flaring is expected for extended discs built up by radial migration, we demonstrate that this observed very strong flaring of the Milky Way disc is more likely consistent with it being dynamically heated by the repeated passage of the Sagittarius dwarf spheroidal galaxy through the midplane.