The G305 H ii complex ( G305.4+0.1 ) is one of the most massive star forming structures yet identified within the Galaxy .
It is host to many massive stars at all stages of formation and evolution , from embedded molecular cores to post main-sequence stars .
Here , we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2 , using HST+NICMOS imaging and VLT+ISAAC spectroscopy .
We find that the spectro-photometric distance to the clusters is consistent with the kinematic distance to the G305 complex , an average of all measurements giving a distance of 3.8 \pm 0.6kpc .
From analysis of the stellar populations and the pre-main-sequence stars we find that Danks 2 is the elder of the two clusters , with an age of 3 ^ { +3 } _ { -1 } Myr .
Danks 1 is clearly younger with an age of 1.5 ^ { +1.5 } _ { -0.5 } Myr , and is dominated by three very luminous H-rich Wolf-Rayet stars which may have masses \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ > $ } } } 100M _ { \normalsize \odot } .
The two clusters have mass functions consistent with the Salpeter slope , and total cluster masses of 8000 \pm 1500M _ { \normalsize \odot } and 3000 \pm 800M _ { \normalsize \odot } for Danks 1 and Danks 2 respectively .
Danks 1 is significantly the more compact cluster of the two , and is one of the densest clusters in the Galaxy with \log ( \rho / M _ { \odot } { pc } ^ { -3 } ) = 5.5 ^ { +0.5 } _ { -0.4 } .
In addition to the clusters , there is a population of apparently isolated Wolf-Rayet stars within the molecular cloud ’ s cavity .
Our results suggest that the star-forming history of G305 began with the formation of Danks 2 , and subsequently Danks 1 , with the origin of the diffuse evolved population currently uncertain .
Together , the massive stars at the centre of the G305 region appear to be clearing away what is left of the natal cloud , triggering a further generation of star formation at the cloud ’ s periphery .