A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

Andrew S. Graus, James S. Bullock, Alex Fitts, Michael C. Cooper, Michael Boylan-Kolchin, Daniel R. Weisz, Andrew Wetzel, Robert Feldmann, Claude André Faucher-Giguère, Eliot Quataert, Philip F. Hopkins, Dusan Keres

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

We explore the radial variation of star formation histories (SFHs) in dwarf galaxies simulated with Feedback In Realistic Environments (FIRE) physics. The sample contains 26 field dwarf galaxies with Mstar = 105–109 M. We find age gradients are common in our dwarfs, with older stars dominant at large radii. The strength of the gradient correlates with overall galaxy age such that earlier star formation produces a more pronounced gradient. The relation between formation time and strength of the gradient is driven by both mergers and star formation feedback. Mergers can both steepen and flatten the age gradient depending on the timing of the merger and SFHs of the merging galaxy. In galaxies without significant mergers, feedback pushes stars to the outskirts. The strength of the age gradient is determined by the subsequent evolution of the galaxy. Galaxies with weak age gradients constantly grow to z = 0, meaning that young star formation occurs at a similar radius to which older stars are heated to. In contrast, galaxies with strong age gradients tend to maintain a constant half-mass radius over time. If real galaxies have age gradients as we predict, stellar population studies that rely on sampling a limited fraction of a galaxy can give a biased view of its global SFH. Central fields can be biased young by Gyrs while outer fields are biased old. Fields positioned near the 2D half-light radius will provide the least biased measure of a dwarf galaxy’s global SFH.

Original languageEnglish (US)
Pages (from-to)1186-1201
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume490
Issue number1
DOIs
StatePublished - 2019
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Cosmology: theory
  • Galaxies: dwarf
  • Galaxies: formation
  • Local Group

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    Graus, A. S., Bullock, J. S., Fitts, A., Cooper, M. C., Boylan-Kolchin, M., Weisz, D. R., Wetzel, A., Feldmann, R., Faucher-Giguère, C. A., Quataert, E., Hopkins, P. F., & Keres, D. (2019). A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies. Monthly Notices of the Royal Astronomical Society, 490(1), 1186-1201. https://doi.org/10.1093/mnras/stz2649