The Brightest Young Star Clusters in NGC 5253

TL;DR

This study uses detailed multi-wavelength Hubble data to accurately determine the ages, masses, and properties of young star clusters in NGC 5253, revealing recent concentrated star formation and the characteristics of the most massive clusters in the starburst region.

Contribution

It provides unprecedentedly precise measurements of cluster properties and insights into the recent star formation history in NGC 5253 using comprehensive spectral energy distribution modeling.

Findings

Clusters are 1-15 Myr old with masses 10^4 to 2.5x10^5 solar masses.

The most massive cluster is ~1 Myr old, in a dust cloud with A_V~50 mag.

Star formation has become more concentrated towards the radio nebula over 15 Myr.

Abstract

The nearby dwarf starburst galaxy NGC5253 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 NGC5253 with wavelength coverage from 1500 Ang to 1.9 micron 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 ~1-15 Myr and masses ~1x10^4 - 2.5x10^5 M_sun. The clusters' spatial location and ages indicate that star formation has become more concentrated towards the radio nebula over the last ~15 Myr. The most massive cluster is in the radio nebula; with a mass 2.5x10^5 M_sun and an age ~1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with A_V~50 mag, and shows a clear nearIR excess, likely from hot dust. The second radio nebula cluster is also ~1 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.