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Table 5:

High-mass young objects in NGC 6334 - NGC 6357 (M > 200 $M_\odot $) at various stages of the high-mass star formation process.


Starless High-mass IR-quiet High-luminosity O-B3 stars
  clumps protostars IR protostars  
NGC 6334 - NGC 6357        
Number 1 6 9 300
$\langle size \rangle$ 0.29 pc 0.38 pc 0.37 pc  
Statistical lifetime[*] $\sim$ $1 \times 10^{4}$ yr $\sim$ $6 \times 10^{4}$ yr $\sim$ $9 \times 10^{4}$ yr $\sim$ $3 \times 10^{6}$ yr
$\langle M\rangle$ 242 $M_\odot $ 571 $M_\odot $ 664 $M_\odot $  
$\langle n_{\rm H_{2}}\rangle$ $4.1 \times 10^{4}$ cm-3 $1.1 \times 10^{5}$ cm-3 $1.9 \times 10 ^{5}$ cm-3  
Free-fall time[*] $4.9 \times 10 ^{4}$ yr $8 \times 10^{4}$ yr  
Cygnus X        
Number[*] 10 17 25 660
Statistical lifetime $3 \times 10^4$ yr $\sim$ $5.1 \times 10^{4}$ yr $\sim$ $7.6 \times 10^{4}$ yr ( $2 \pm 1) \times 10^{6}$ yr
Free-fall time $4 \times 10^{5}$ yr $8 \times 10^{4}$ yr  

Statistical lifetime 		$2 \times 10^{5}$ yr $2 \times 10^{4}$ yr $2 \times 10^{5}$ yr  
in dark clouds        

Notes. (1) Lifetime calculated relative to the known age of the stars in the young cluster Pismis 24 (cf. Massey et al. 2001 and Ahumada et al. 2007) using the census given in line 1. (2) Free-fall time measured from the mean values of the volume-averaged density given line 5: $t_{\rm free-fall} = \sqrt{\frac{3 \pi}{32 G \langle \rho \rangle}}$ (3) The numbers of OB3 stars in Cygnus X and thus the statistical lifetimes of high-mass young stellar objects have been corrected from the values given in Motte et al. (2007).


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