The nearby dwarf starburst galaxy NGCÂ 5253 hosts a number of young , massive star clusters , the two youngest of which are centrally concentrated and surrounded by thermal radio emission ( the ‘ radio nebula ’ ) .
To investigate the role of these clusters in the starburst energetics , we combine new and archival Hubble Space Telescope images of NGCÂ 5253 with wavelength coverage from 1500Â Ã Â to 1.9Â \mu m in 13 filters .
These include H \alpha , P \beta , and P \alpha , and the imaging from the Hubble Treasury Program LEGUS ( Legacy Extragalactic UV Survey ) .
The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages , masses , and extinctions of the 9 optically brightest clusters ( M _ { V } < - 8.8 ) and the two young radio nebula clusters .
The clusters have ages \sim 1–15Â Myr and masses \sim 1 \times 10 ^ { 4 } -2.5 \times 10 ^ { 5 } Â M _ { \odot } .
The clusters ’ spatial location and ages indicate that star formation has become more concentrated towards the radio nebula over the last \sim 15 Â Myr .
The most massive cluster is in the radio nebula ; with a mass \sim 2.5 \times 10 ^ { 5 } Â M _ { \odot } and an age \sim 1Â Myr , it is 2–4 times less massive and younger than previously estimated .
It is within a dust cloud with A _ { V } \sim 50 Â mag , and shows a clear nearIR excess , likely from hot dust .
The second radio nebula cluster is also \sim 1Â Myr old , confirming the extreme youth of the starburst region .
These two clusters account for about half of the ionizing photon rate in the radio nebula , and will eventually supply about 2/3 of the mechanical energy in present-day shocks .
Additional sources are required to supply the remaining ionizing radiation , and may include very massive stars .