We present Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) images ofthe merger remnant NGC 7252. In particular, we focus on the surface brightnessprofiles and effective radii, Reff, of 36 young massive clusters (YMCs) withinthe galaxy. All the clusters have masses exceeding 10^5 Msun and are, despitethe 64 Mpc distance to the galaxy, (partly) resolved on the HST images. Effective radii can be measured down to ~2.5 pc, and the largest clusters haveReff approaching 20 pc. The median Reff of our sample clusters is ~6-7 pc,which is larger than typical radii of YMCs (~2.5 pc). This could be due to oursample selection (only selecting resolved sources) or to an intrinsicmass--radius relation within the cluster population. We find at least threeclusters that have power-law profiles of the Elson, Fall, & Freeman (1987,"EFF") type extending out to >150 pc. Among them are the two most massiveclusters, W3 and W30, which have profiles that extend to at least 500 and 250pc, respectively. Despite their extended profiles, the effective radii of thethree clusters are 17.2, 12.6 and 9.1 pc for W3, W26 and W30, respectively. Wecompare these extended profiles with those of YMCs in the LMC (R136 in 30 Dor),the Antennae galaxies (Knot S) and in the nearby spiral galaxy NGC 6946. Extended profiles seem to be a somewhat common feature, even though many nearbyYMCs show distinct truncations. A continuous distribution between these twoextremes, i.e. truncated or extremely extended, is the most likelyinterpretation. We suggest that the presence or absence of an extended envelopein {em very young clusters} may be due to the gas distribution of theproto-cluster giant molecular cloud, in particular if the proto-cluster corebecomes distinct from the surrounding gas before star formation begins.
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