Star Formation Sites toward the Galactic Center Region: The Correlation
  of CH3OH Masers, H2O Masers, and Near-IR Green Sources
  We present a study of star formation in the Central Molecular Zone (CMZ) of
our Galaxy through the association of three star formation indicators: 6.7 GHz
CH3OH masers, 22 GHz H2O masers, and enhanced 4.5 micron emission (`green')
sources. We explore how star formation in the Galactic center (l < 1.3 deg, |b|
< 10', where l and b are Galactic longitude and Galactic latitude) compares
with that of the Galactic disk (6 deg < l < 345 deg, |b| < 2 deg). Using an
automated algorithm, we search for enhanced 4.5 micron emission sources toward
6.7 GHz CH3OH masers detected in the Parkes Methanol Multibeam Survey. We
combine these results with our 22 GHz H2O maser survey of the CMZ carried out
with the Mopra telescope. We find that the correlation of CH3OH masers with
green sources is a function of Galactic latitude, with a minimum close to b=0
and increasing with |b| (toward the central part of the Galaxy, 6 deg < l < 345
deg, |b| < 2 deg). We find no significant difference between the correlation
rate of CH3OH masers with green sources in the CMZ and the disk. This suggests
that although the physical conditions of the gas are different in the Galactic
center from that of the Galactic disk, once gravitational instability sets in
at sufficiently high densities, signatures of star formation appear to be
similar in both regions. Moreover, the detection of green sources, even at the
distance of the Galactic center, shows that our technique can easily identify
the early stages of star formation, especially in low extinction regions of the
Galaxy. Through the association of H2O and CH3OH masers, we identify 15
star-forming sites in the CMZ. We find no coincident H2O and CH3OH masers
outside the CMZ (with limited H2O maser survey coverage outside the CMZ),
possibly indicating a difference in the maser evolutionary sequence for
star-forming cores in the Galactic center region and the disk.
