HST study of star cluster in LEGUS galaxies

We classify 3757 star clusters in 16 nearby galaxies according to their H{alpha} morphology (concentrated, partially exposed, no emission), using Hubble Space Telescope (HST) imaging from the Legacy ExtraGalactic Ultraviolet Survey (LEGUS).

We find : (1) The mean SED ages of clusters with concentrated (1-2 Myr) and partially exposed H II region morphologies (2-3 Myr) indicate a relatively early onset of gas clearing and a short (1-2 Myr) clearing time-scale. (2) The reddening of clusters can be overestimated due to the presence of red supergiants, which is a result of stochastic sampling of the IMF in low mass clusters. (3) The age-reddening degeneracy impacts the results of the SED fitting - out of 1408 clusters with M* => 5000 M_{sun}_, we find that at least 46 (3 per cent) have SED ages which appear significantly underestimated or overestimated based on H {alpha} and their environment, while the total percentage of poor age estimates is expected to be several times larger.