A Headless Tadpole Galaxy: The High Gas-phase Metallicity of the Ultra-diffuse Galaxy UGC 2162

Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.; Elmegreen, D. M.; Filho, M.; Muñoz-Tuñón, C.; Pérez-Montero, E.; Román, J.
Bibliographical reference

The Astrophysical Journal, Volume 869, Issue 1, article id. 40, 7 pp. (2018).

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The cosmological numerical simulations tell us that accretion of external metal-poor gas drives star formation (SF) in galaxy disks. One the best pieces of observational evidence supporting this prediction is the existence of low-metallicity star-forming regions in relatively high-metallicity host galaxies. The SF is thought to be fed by metal-poor gas recently accreted. Since the gas accretion is stochastic, there should be galaxies with all the properties of a host but without the low-metallicity starburst. These galaxies have not been identified yet. The exception may be UGC 2162, a nearby ultra-diffuse galaxy (UDG) that combines low surface brightness and relatively high metallicity. We confirm the high metallicity of UGC 2162 (12+{log}({{O}}/{{H}})={8.52}-0.24+0.27) using spectra taken with the 10 m GTC telescope. UGC 2162 has the stellar mass, metallicity, and star formation rate surface density expected for a host galaxy in between outbursts. This fact suggests a physical connection between some UDGs and metal-poor galaxies, which may be the same type of object in a different phase of the SF cycle. UGC 2162 is a high-metallicity outlier of the mass–metallicity relation, a property shared by the few UDGs with known gas-phase metallicity.
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Starsbursts play a key role in the cosmic evolution of galaxies, and thus in the star formation (SF) history of the universe, the production of metals, and the feedback coupling galaxies with the cosmic web. Extreme SF conditions prevail early on during the formation of the first stars and galaxies, therefore, the starburst phenomenon constitutes a

Muñoz Tuñón