Constraining the population of isolated massive stars within the Central
  Molecular Zone
  Many galaxies host pronounced circumnuclear starbursts, fuelled by infalling
gas. Such activity is expected to drive the secular evolution of the nucleus
and generate super winds, while the intense radiation fields and extreme gas
and cosmic ray densities present may act to modify the outcome of star
formation with respect to more quiescent galactic regions. The centre of the
Milky Way is the only example of this phenomenon where, by virtue of its
proximity, individual stars may be resolved. Previous studies have revealed
that it hosts a rich population of massive stars; these are located within
three clusters, with an additional contingent dispersed throughout the Central
Molecular Zone (CMZ). We employed VLT+KMOS to obtain homogeneous, high S/N
spectroscopy of the later cohort for classification and quantitative analysis.
Including previously identified examples, we found a total of 83 isolated
massive stars within the Galactic Centre, which are biased towards objects
supporting powerful stellar winds and/or extensive circumstellar envelopes. No
further stellar clusters, or their tidally stripped remnants, were identified,
although an apparent stellar overdensity was found to be coincident with the
Sgr B1 star forming region. The cohort of isolated massive stars within the CMZ
is comparable in size to that of the known clusters but, due to observational
biases, is likely highly incomplete at this time. Combining both populations
yields over 320 spectroscopically classified stars that are expected to undergo
core collapse within the next 20Myr. Given that this is presumably an
underestimate of the true number, the population of massive stars associated
with the CMZ appears unprecedented amongst star formation complexes within the
Milky Way, and one might anticipate that they play a substantial role in the
energetics and evolution of the nuclear region.
