The O star hinterland of the Galactic starburst, NGC 3603
  The very bright and compact massive young cluster, NGC 3603, has been cited
as an example of a starburst in the Milky Way and compared with the
much-studied R136/30 Doradus region in the Large Magellanic Cloud. Here we
build on the discovery by Mohr-Smith et al. (2017) of a large number of
reddened O stars around this cluster. We construct a list of 288 candidate O
stars with proper motions, in a region of sky spanning 1.5x1.5 square degrees
centered on NGC 3603, by cross-matching the Mohr-Smith et al. (2017) catalogue
with Gaia DR2 (Gaia Collaboration et al. 2018). This provides the basis for a
first comprehensive examination of the proper motions of these massive stars in
the halo of NGC 3603, relative to the much better studied central region. We
identify up to 11 likely O star ejections -- 8 of which would have been ejected
between 0.60 and 0.95 Myr ago (supporting the age of c.1 Myr that has been
attributed to the bright cluster centre). Seven candidate ejections are
arranged in a partial ring to the south of the cluster core spanning radii of
9-18 arcmin (18-36 pc if the cluster is 7 kpc away). We also show that the
cluster has a halo of a further 100 O stars extending to a radius of at least 5
arcmin, adding to the picture of NGC 3603 as a scaled down version of the
R136/30 Dor region.
