The population of hot subdwarf stars studied with Gaia II. The Gaia DR2
  catalogue of hot subluminous stars
  Based on data from the ESA Gaia Data Release 2 (DR2) and several
ground-based, multi-band photometry surveys we compiled an all-sky catalogue of
$39\,800$ hot subluminous star candidates selected in Gaia DR2 by means of
colour, absolute magnitude and reduced proper motion cuts. We expect the
majority of the candidates to be hot subdwarf stars of spectral type B and O,
followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB
stars, and central stars of planetary nebulae. The contamination by cooler
stars should be about $10\%$. The catalogue is magnitude limited to Gaia
$G<19\,{\rm mag}$ and covers the whole sky. Except within the Galactic plane
and LMC/SMC regions, we expect the catalogue to be almost complete up to about
$1.5\,{\rm kpc}$. The main purpose of this catalogue is to serve as input
target list for the large-scale photometric and spectroscopic surveys which are
ongoing or scheduled to start in the coming years. In the long run, securing a
statistically significant sample of spectroscopically confirmed hot subluminous
stars is key to advance towards a more detailed understanding of the latest
stages of stellar evolution for single and binary stars.
