Massive (> 10,000 solar mass) young star clusters and OB associations
dominate the energetic feedback from stars into the interstellar medium.
They contain the most massive and luminous stars in the Galaxy,
which shape their environments through winds, ionizing flux, radiation pressure,
and eventually supernovae, destroying natal molecular clouds and inflating superbubbles.
We develop a method, based on differential extinction of the Galactic disk,
to search for massive star clusters powering most luminous star forming
complexes in the Galaxy identified in the WMAP foreground maps. As results,
we identify 25 candidate clusters within 40 star forming complexes having extinctions
consistent with their distances. One notable example is the discovery of
the Dragonfish association which is the most luminous OB association in the Galaxy
powering a giant nebula at 10 kpc across the Galactic plane.
Using near-infrared spectroscopy, we identify two Luminous Blue Variable candidates,
one Wolf-Rayet, 15 O-type stars (including one possible runaway) out of 50 sampled
stars located within the boundary of this association, which is consistent with the expected
total number of OB stars greater than 400. The mass of the Dragonfish association is
100,000 solar mass, similar to that of Westerlund 1 known to be the most massive star cluster.
These results, hence, offer an important opportunity to study the formation and evolution
of most massive star clusters. We will discuss ongoing and planned follow-up observations
of these new massive star clusters as well as the development of Wide Integral Field
Infrared Spectrograph which is ideal to study them.