An accurate age for the enigmatic galaxy NGC1052-DF2
Abstract
The galaxy NGC1052-DF2 has been the subject of intense debate in the literature. Not only does it seem to have a very low dark matter content, it also has a peculiar population of very bright globular clusters that make up 3% of the total light. A central question is when the galaxy and its unusual globular clusters were formed. The best constraints have come from optical spectroscopy of the bright globular clusters. The clusters have a metallicity of [Fe/H]=-1.4 and an apparent age of 9 Gyr, consistent with constraints on the metallicity and age of the diffuse light. However, these age measurements are only lower limits, due to the unknown contribution of blue horizontal branch (BHB) stars to the integrated light. If the BHB branch is as strong as in Milky Way globular clusters of the same metallicity, the true age of the globular clusters, and the galaxy, could be 13 Gyr - predating the formation of the massive elliptical galaxy NGC1052. The objective of this proposal is to measure the contribution of hot stars to the integrated light by obtaining F225W UV imaging of NGC1052-DF2 and its globular clusters with UVIS. The F225W-F814W color is sensitive to hot stars and breaks the degeneracy between age and the strength of the BHB. This measurement will pin down the formation epoch of the galaxy, currently only constrained to be at least 9 Gyr ago; determine whether the globular clusters all have identical UV properties or show variation in their F225W-F814W colors like luminous Milky Way clusters; and test the hypothesis that a significant fraction of the diffuse light comes from disrupted globular clusters.
- Publication:
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HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15850V