YOUNG STARS AT THE EDGE: STELLAR CLUSTERING IN THE OUTER REGIONS OF THE M33 DISK

We investigate the distribution of bright main-sequence stars near the northern edge of the M33 disk. Clustering on sub-kiloparsec scales is seen among stars with ages similar to 10 Myr, and two large star-forming complexes are identified. Similar large-scale grouping is not evident among stars with ages 100 Myr. Stars of this age are also distributed over a much larger area than those with younger ages, and it is argued that random stellar motions alone, as opposed to orderly motions of the type spurred by large-scale secular effects, can re-distribute stars out to distances of at least 2 kpc (i.e., one disk scale length) from their birthplaces on 100 Myr timescales. Such random motions may thus play a significant role in populating the outer regions of the M33 disk. Finally, it is suggested that-to the extent that the ambient properties of the outer disk mirror those in the main body of the disk-stars in this part of M33 may have formed in star clusters with masses 50-250 M-circle dot, which is substantially lower than the peak predicted for the solar neighborhood initial cluster mass function.