SIMBAD references

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 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 three SSCs at the center of NGC 5253. At optical wavelengths, the two SSCs lie on either side of the supernebula, which coincides with a highly obscured region. In the infrared, all three 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 are 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.