Table 6
Median properties and lifetime estimates for MDCs of different evolutionary states.
| IR-bright MDC | IR-quiet MDC | starless MDC candidate | O-B3 stars | |
|
|
||||
| Number | 6 | 10 | 16 | 150 |
| Size (pc) | 0.08 | 0.11 | 0.14 | – |
| ⟨ Tdust ⟩ (K) | 29 | 16 | 15 | – |
| Lbol (L⊙) | 9500 | 760 | 130 | – |
| Mass (M⊙) | 140 | 106 | 103 | – |
| ⟨ nH2 ⟩ (cm-3) | 1.4 × 107 | 3.1 × 106 | 1.4 × 106 | – |
| Free-fall time1 | 9 × 103 yr | 2 × 104 yr | 3 × 104 yr | – |
| Number of high-mass cores2 | 32 high-mass protostars | 1−7 high-mass prestellar cores | – | |
| Statistical lifetime of high-mass cores3 | 3 × 105 yr | 1−7 × 104 yr | 1.5 × 106 yr | |
Notes.
Free-fall time measured from the median values of the density averaged over the full MDC volume, which is approximately a sphere with a FWHM radius: ⟨ nH2 ⟩ full = ⟨ nH2 ⟩ /8 and 
.
We assumed that protostellar MDCs host ~2 protostars as was found for Cygnus-X by Bontemps et al. (2010), while 1 to 7 starless MDCs could host one high-mass prestellar core.
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