Low Metallicities and Old Ages for Three Ultra-diffuse Galaxies in the Coma Cluster

Meng Gu, Charlie Conroy, David Law, Pieter Van Dokkum, Renbin Yan, David Wake, Kevin Bundy, Allison Merritt, Roberto Abraham, Jielai Zhang, Matthew Bershady, Dmitry Bizyaev, Jonathan Brinkmann, Niv Drory, Kathleen Grabowski, Karen Masters, Kaike Pan, John Parejko, Anne Marie Weijmans, Kai Zhang

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF 7, DF 44, and DF 17, which have central surface brightnesses of μ g ≈24.4-25.1 mag arcsec-2. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hr of on-source integration, we achieved a mean signal-to-noise ratio in the optical of 9.5 ∗-1, 7.9 ∗-1, and 5.0 ∗-1, respectively, for DF 7, DF 44, and DF 17. Stellar population models applied to these spectra enable measurements of recession velocities, ages, and metallicities. The recession velocities of DF 7, DF 44, and DF 17 are km s-1, km s-1, and km s-1, spectroscopically confirming that all of them reside in the Coma cluster. The stellar populations of these three galaxies are old and metal-poor, with ages of Gyr, Gyr, and Gyr, and iron abundances of [Fe/H] , , and , respectively. Their stellar masses are (3-6) ×108 M o. The UDGs in our sample are as old or older than galaxies at similar stellar mass or velocity dispersion (only DF 44 has an independently measured dispersion). They all follow the well-established stellar mass-stellar metallicity relation, while DF 44 lies below the velocity dispersion-metallicity relation. These results, combined with the fact that UDGs are unusually large for their stellar masses, suggest that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness.

Original languageEnglish
Article number37
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 2018

Bibliographical note

Funding Information:
We thank the referee for helpful comments that improved this paper. M.G. acknowledges support from the National Science Foundation Graduate Research Fellowship. C.C. acknowledges support from NASA grant NNX15AK14G, NSF grant AST-1313280, and the Packard Foundation. M.B. acknowledges funding from NSF/AST-1517006. A.W. acknowledges support of a Leverhulme Trust Early Career Fellowship. The computations in this paper were run on the Odyssey cluster supported by the FAS Division of Science, Research Computing Group at Harvard University.

Funding Information:
Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS website ishttp://www.sdss.org.

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.


  • galaxies: clusters: individual (Coma)
  • galaxies: evolution
  • galaxies: stellar content

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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