Star formation at the edge of the Local Group: A rising star formation history in the isolated galaxy WLM

Saundra M. Albers, Daniel R. Weisz, Andrew A. Cole, Andrew E. Dolphin, Evan D. Skillman, Benjamin F. Williams, Michael Boylan-Kolchin, James S. Bullock, Julianne J. Dalcanton, Philip F. Hopkins, Ryan Leaman, Alan W. McConnachie, Mark Vogelsberger, Andrew Wetzel

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

We present the star formation history (SFH) of the isolated (D ∼ 970 kpc) Local Group dwarf galaxy Wolf-Lundmark-Melotte (WLM) measured from colour-magnitude diagrams (CMDs) constructed from deep Hubble Space Telescope imaging. Our observations include a central (0.5 rh) and outer field (0.7 rh) that reach below the oldest main-sequence turn-off. WLM has no early dominant episode of star formation: 20 per cent of its stellar mass formed by ∼12.5 Gyr ago (z ∼ 5). It also has an SFR that rises to the present with 50 per cent of the stellar mass within the most recent 5 Gyr (z < 0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark-matter core creation. The SFHs of real isolated dwarf galaxies and those from the Feedback in Realistic Environment suite are in good agreement for M*(z = 0) ∼ 107-109M☉, but in worse agreement at lower masses (M*(z = 0) ∼ 105-107 M☉). These differences may be explainable by systematics in the models (e.g. reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.

Original languageEnglish (US)
Pages (from-to)5538-5550
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume490
Issue number4
DOIs
StatePublished - Dec 1 2019

Bibliographical note

Funding Information:
This study is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programme 13768. The authors thank Shea Garrison-Kimmel and Andrew Graus for sharing results from their dwarf galaxy simulations and Piero Madau and Peter Behroozi for helpful comments during the editing process. Support for this work was provided by NASA through grants HST-GO-13768, HST-GO-15006, and JWST-ERS-1334 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. SMA is supported by the National Science Foundation Graduate Research Fellowship under Grant DGE 1752814. DRW acknowledges support from an Alfred P. Sloan Fellowship and an Alexander von Humboldt Fellowship. MBK acknowledges support from NSF grant AST-1517226 and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-14282, HST-AR-14554, and HST-GO-14191 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. This research has made use of NASA’s Astrophysics Data System Bibliographic Services and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Funding Information:
This study is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programme 13768. The authors thank Shea Garrison-Kimmel and Andrew Graus for sharing results from their dwarf galaxy simulations and Piero Madau and Peter Behroozi for helpful comments during the editing process. Support for this work was provided by NASA through grants HST-GO-13768, HST-GO-15006, and JWST-ERS-1334 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. SMA is supported by the National Science Foundation Graduate Research Fellowship under Grant DGE 1752814. DRW acknowledges support from an Alfred P. Sloan Fellowship and an Alexander von Humboldt Fellowship. MBK acknowledges support from NSF grant AST-1517226 and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-14282, HST-AR-14554, and HST-GO-14191 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. This research has made use of NASA's Astrophysics Data System Bibliographic Services and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Keywords

  • Galaxies: dwarf
  • Galaxies: evolution
  • Galaxies: stellar content
  • Local Group

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