Star Formation in the Central 400 pc of the Milky Way: Evidence for a
  Population of Massive YSOs
  The central kpc of the Milky Way might be expected to differ significantly
from the rest of the Galaxy with regard to gas dynamics and the formation of
YSOs. We probe this possibility with mid-infrared observations obtained with
IRAC and MIPS on Spitzer and with MSX. We use color-color diagrams and SED fits
to explore the nature of YSO candidates (including objects with 4.5 micron
excesses possibly due to molecular emission). There is an asymmetry in the
distribution of the candidate YSOs, which tend to be found at negative Galactic
longitudes; this behavior contrasts with that of the molecular gas,
approximately 2/3 of which is at positive longitudes. The small scale height of
these objects suggests that they are within the Galactic center region and are
dynamically young. They lie between two layers of infrared dark clouds and may
have originated from these clouds. We identify new sites for this recent star
formation. The methanol masers appear to be associated with young, embedded
YSOs characterized by 4.5 micron excesses. We use the SEDs of these sources to
estimate their physical characteristics. Within the central 400x50 pc
(|l|<1.3\degr and |b|<10') the star formation rate based on the identification
of Stage I evolutionary phase of YSO candidates is about 0.14 solar mass/yr. We
suggest that a recent burst of star formation took place within the last 10^5
years. This suggestion is also consistent with estimates of star formation
rates within the last ~10^7 years showing a peak around 10^5 years ago. Lastly,
we find that the Schmidt-Kennicutt Law applies well in the central 400 pc of
the Galaxy. This implies that star formation does not appear to be dramatically
affected by the extreme physical conditions in the Galactic center region.
