Matthew S. Povich Research
Spitzer/MIPSGAL 24 micron image of the M17 SWex infrared dark cloud, with positions of 488 candidate young stellar objects (YSOs) overlaid (from Povich & Whitney 2010). Colors identify YSO evolutionary stages from modeling each source—red: emission dominated by accreting envelopes; yellow: dominated by optically thick circumstellar disks; green: optically thin disks; and cyan: ambiguous. YSOs with excess emission at 4.5 microns, thought to be an indication of outflow activity, are marked by diamonds.
 
Matthew S. Povich Research
Distribution of YSOs in the M17 SWex sample as a function of stellar mass from models (the YSO mass function; Povich & Whitney 2010). The remarkable feature of this distribution is the departure from the expected power-law slope (black curve) at the high-mass end. The steeper slope observed (red curve) is a selection effect arising from the more rapid destruction of circumstellar disks around more massive YSOs. The complete lack of stars more massive than 20 solar masses is mysterious—we have interpreted it as evidence that massive star formation has been delayed in this cloud.