Context :

Aims : The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties .
Here , we aim to quantitatively investigate the strikingly low radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars ( \sigma _ { \mathrm { 1 D } } = 5.6 \pm 0.2 km s ^ { -1 } ) in the very young massive star forming region M17 , in order to obtain first constraints on the multiplicity properties of young massive stellar objects .

Methods : We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained \sigma _ { \mathrm { 1 D } } distributions to the observed value .
We specifically investigate two scenarios : a low binary fraction and a dearth of short-period binary systems .

Results : Simulated populations with low binary fractions ( f _ { \mathrm { bin } } = 0.12 _ { -0.09 } ^ { +0.16 } ) or with truncated period distributions ( P _ { \mathrm { cutoff } } > 9 months ) are able to reproduce the low \sigma _ { \mathrm { 1 D } } observed within their 68 % -confidence intervals .
Furthermore , parent populations with f _ { \mathrm { bin } } > 0.42 or P _ { \mathrm { cutoff } } < 47 d can be rejected at the 5 % -significance level .
Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old , well characterized OB-type populations .
To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process .
In the context of the second scenario , compact binaries must form later on , and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks .

Conclusions : If the obtained constraints for the M17 ’ s massive-star population are representative of the multiplicity properties of massive young stellar objects , our results may provide support to a massive star formation process in which binaries are initially formed at larger separations , then harden or migrate to produce the typical ( untruncated ) power-law period distribution observed in few Myr-old OB binaries .