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arXiv · 2309.15148

The star formation histories of quiescent ultra-diffuse galaxies and their dependence on environment and globular cluster richness

Anna Ferré-Mateu·Jonah S. Gannon·Duncan A. Forbes·Maria Luisa Buzzo·Aaron J. Romanowsky·Jean P. Brodie
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Abstract

We derive the stellar population parameters of 11 quiescent ultra-diffuse galaxies (UDGs) from Keck/KCWI data. We supplement these with 14 literature UDGs, creating the largest spectroscopic sample of UDGs to date (25). We find a strong relationship between their $\alpha$-enhancement and their star formation histories: UDGs that formed on very short timescales have elevated [Mg/Fe] abundance ratios, whereas those forming over extended periods present lower values. Those forming earlier and faster are overall found in high-density environments, being mostly early infalls into the cluster. No other strong trends are found with infall times. We analyze the stellar mass-metallicity, age-metallicity and [Mg/Fe]-metallicity relations of the UDGs, comparing them to other types of low mass galaxies. Overall, UDGs scatter around the established stellar mass--metallicity relations of classical dwarfs. We find that GC-rich UDGs have intermediate-to-old ages, but previously reported trends of galaxy metallicity and GC richness are not reproduced with this spectroscopic sample due to the existence of GC-rich UDGs with elevated metallicities. In addition, we also find that a small fraction of UDGs could be 'failed-galaxies', supported by their GC richness, high $\alpha$-abundances, fast formation timescales and that they follow the mass-metallicity relation of z~2 galaxies. Finally, we also compare our observations to simulated UDGs. We caution that there is not a single simulation that can produce the diverse UDG properties simultaneously, in particular the low metallicity failed-galaxy like UDGs.

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Anna Ferré-Mateu, Jonah S. Gannon, Duncan A. Forbes, Maria Luisa Buzzo, Aaron J. Romanowsky, Jean P. Brodie. 2023-09-26. The star formation histories of quiescent ultra-diffuse galaxies and their dependence on environment and globular cluster richness. https://arxiv.org/abs/2309.15148

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