Journal
ASTROPHYSICAL JOURNAL
Volume 870, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/aaef8c
Keywords
astrometry; open clusters and associations: general; stars: formation; stars: kinematics and dynamics
Categories
Funding
- NASA [NNX15AF42G]
- Chandra grants [AR7-18002X, GO7-18001X, G06-17015x]
- Chandra ACIS Team by the Chandra X-ray Center [SV474018, NAS8-03060]
- NASA [NNX15AF42G, 805012] Funding Source: Federal RePORTER
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The Gaia mission has opened a new window into the internal kinematics of young star clusters at the sub-km s(-1) level, with implications for our understanding of how star clusters form and evolve. We use a sample of 28 clusters and associations with ages from similar to 1-5 Myr, where lists of members are available from previous X-ray, optical, and infrared studies. Proper motions from Gaia DR2 reveal that at least 75% of these systems are expanding; however, rotation is only detected in one system. Typical expansion velocities are on the order of similar to 0.5 km s(-1), and in several systems, there is a positive radial gradient in expansion velocity. Systems that are still embedded in molecular clouds are less likely to be expanding than those that are partially or fully revealed. One-dimensional velocity dispersions, which range from sigma(1D) = 1 to 3 km s(-1), imply that most of the stellar systems in our sample are supervirial and that some are unbound. In star-forming regions that contain multiple clusters or subclusters, we find no evidence that these groups are coalescing, implying that hierarchical cluster assembly, if it occurs, must happen rapidly during the embedded stage.
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