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Extreme chemical abundance ratio suggesting an exotic origin for an ultradiffuse galaxy
Monthly Notices of the Royal Astronomical Society (2019)
  • Ignacio Martín-Navarro, University of California Observatories
  • Aaron J. Romanowsky, San Jose State University
  • Jean P. Brodie, University of California Observatories
  • Anna Ferr´e-Mateu, Swinburne University of Technology
  • Adebusola Alabi, University of California Observatories
  • Duncan A. Forbes, Swinburne University of Technology
  • Margarita Sharina, Russian Academy of Sciences
  • Alexa Villaume, University of California Observatories
  • Viraj Pandya, University of California Observatories
  • David Martinez-Delgado, Universität Heidelberg
Ultradiffuse galaxies (UDGs) are a population of extended galaxies but with relatively low luminosities. The origin of these objects remains unclear, largely due to the observational challenges of the low surface brightness Universe. We present here a detailed stellar population analysis of a relatively isolated UDG, DGSAT I, based on spectroscopic data from the Keck Cosmic Web Imager integral field unit. The star formation history of DGSAT I seems to be extended, with a mean luminosity-weighted age of ∼3 Gyr, in agreement with previous photometric studies. However, we find a very high [Mg/Fe] abundance ratio, which is extreme even in the context of the highly alpha-enhanced massive ellipticals and ultrafaint dwarfs. The [Mg/Fe] enhancement of DGSAT I appears to be 10 times higher than the most magnesium-enhanced stellar systems discovered to date, and suggests that the chemical enrichment of this object was dominated by core-collapse supernovae. Intriguingly, this breaks the canonical relation between [Mg/Fe] and star formation time-scale. With a measured velocity dispersion of 56 ± 10 km s−1, DGSAT I also shows a high-mass-to-light ratio, which indicates that it is highly dark matter dominated. The metal-poor conditions of DGSAT I may have enhanced the formation of massive stars, while at the same time, additional mechanisms are needed to prevent iron-rich yields from being recycled into stars. These results suggest that some UDGs could have experienced chemical enrichment episodes similar to the first building blocks of galaxies.
  • galaxies: abundances,
  • galaxies: evolution,
  • galaxies: formation,
  • galaxies: stellar content
Publication Date
April, 2019
Publisher Statement
This article was published in Monthly Notices of the Royal Astronomical Society ©: 2019 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
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Citation Information
Ignacio Martín-Navarro, Aaron J. Romanowsky, Jean P. Brodie, Anna Ferr´e-Mateu, et al.. "Extreme chemical abundance ratio suggesting an exotic origin for an ultradiffuse galaxy" Monthly Notices of the Royal Astronomical Society Vol. 484 Iss. 3 (2019) p. 3425 - 3433 ISSN: 0035-8711
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