Local spiral structure based on the Gaia EDR3 parallaxes
  Context. The astrometric satellite Gaia is expected to significantly increase
our knowledge as to the properties of the Milky Way. The Gaia Early Data
Release 3 (Gaia EDR3) provides the most precise parallaxes for many OB stars,
which can be used to delineate the Galactic spiral structure. Aims. We
investigate the local spiral structure with the largest sample of
spectroscopically confirmed young OB stars available to date, and we compare it
with what was traced by the parallax measurements of masers. Methods. A sample
consisting of three different groups of massive young stars, including O-B2
stars, O-B0 stars and O-type stars with parallax accuracies better than 10% was
compiled and used in our analysis. Results. The local spiral structures in all
four Galactic quadrants within $\approx$5 kpc of the Sun are clearly delineated
in detail. The revealed Galactic spiral pattern outlines a clear sketch of
nearby spiral arms, especially in the third and fourth quadrants where the
maser parallax data are still absent. These O-type stars densify and extend the
spiral structure constructed by using the Very Long Baseline Interferometry
(VLBI) maser data alone. The clumped distribution of O-type stars also
indicates that the Galaxy spiral structure is inhomogeneous.
