A dearth of young and bright massive stars in the Small Magellanic Cloud
  Massive star evolution at low metallicity is closely connected to many fields
in high-redshift astrophysics, but poorly understood. The Small Magellanic
Cloud (SMC) is a unique laboratory to study this because of its metallicity of
0.2 Zsol, its proximity, and because it is currently forming stars. We used a
spectral type catalog in combination with GAIA magnitudes to calculate
temperatures and luminosities of bright SMC stars. By comparing these with
literature studies, we tested the validity of our method, and using GAIA data,
we estimated the completeness of stars in the catalog as a function of
luminosity. This allowed us to obtain a nearly complete view of the most
luminous stars in the SMC. When then compared with stellar evolution
predictions. We also calculated the extinction distribution, the ionizing
photon production rate, and the star formation rate. Our results imply that the
SMS hosts only 30 very luminous main-sequence stars (M > 40 Msol; L > 10^5
Lsol), which are far fewer than expected from the number of stars in the
luminosity range 3*10^4 < L/Lsol < 3*10^5 and from the typically quoted star
formation rate in the SMC. Even more striking, we find that for masses above M
> 20 Msol, stars in the first half of their hydrogen-burning phase are almost
absent. This mirrors a qualitatively similar peculiarity that is known for the
Milky Way and Large Magellanic Cloud. This amounts to a lack of
hydrogen-burning counterparts of helium-burning stars, which is more pronounced
for higher luminosities. We argue that a declining star formation rate or a
steep initial mass function are unlikely to be the sole explanations for the
dearth of young bright stars. Instead, many of these stars might be embedded in
their birth clouds, although observational evidence for this is weak. We
discuss implications for cosmic reionization and the top end of the initial
mass function.
