The Three Young Nuclear Super Star Clusters in NGC 5253
  The blue compact dwarf galaxy NGC 5253 hosts a very young central starburst.
The center contains intense radio thermal emission from a massive ultracompact
H II region (or "supernebula") and two massive and very young super star
clusters (SSCs), which are seen at optical and infrared wavelengths. The
spatial correspondence between these three objects over an area of < 0.5 arcsec
is very uncertain, and it is usually assumed that one of the optically-detected
SSCs coincides with the supernebula. Using the Gaia Data Release 2 catalog, we
improve the absolute astrometry of Hubble Space Telescope ultraviolet, optical
and infrared images by a factor of ~10 and match them to the radio observations
with an accuracy of 10-20 mas. We find that there are 3 SSCs at the center of
NGC 5253. At optical wavelengths, the two SSCs lie either side of the
supernebula, which coincides with a highly obscured region. In the infrared,
all 3 SSCs are seen with the supernebula dominating at the longest wavelengths.
We examine the properties of the SSCs, which have ages of ~ 1 Myr, are very
compact (<0.6 pc) and separated by projected distances of only 1.5 and 5.8 pc.
It seems likely that they will merge and may form the building blocks for
nuclear star clusters.
