COMPARING M31 AND MILKY WAY SATELLITES: THE EXTENDED STAR FORMATION HISTORIES OF ANDROMEDA II AND ANDROMEDA XVI

Daniel R. Weisz*, Evan D. Skillman, Sebastian L. Hidalgo, Matteo Monelli, Andrew E. Dolphin, Alan McConnachie, Edouard J. Bernard, Carme Gallart, Antonio Aparicio, Michael Boylan-Kolchin, Santi Cassisi, Andrew A. Cole, Henry C. Ferguson, Mike Irwin, Nicolas F. Martin, Lucio Mayer, Kristen B. W. McQuinn, Julio F. Navarro, Peter B. Stetson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We present the first comparison between the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites. Using the Advanced Camera for Surveys on board the Hubble Space Telescope, we obtained deep optical imaging of Andromeda II (And II; M-V = -12.0; log(M-star/M-circle dot) similar to 6.7) and Andromeda XVI (And XVI; M-V = -7.5; log(M-star/M-circle dot) similar to 4.9) yielding color-magnitude diagrams that extend at least 1 mag below the oldest main-sequence turnoff, and are similar in quality to those available for the MW companions. And II and And XVI show strikingly similar SFHs: both formed 50%-70% of their total stellar mass between 12.5 and 5 Gyr ago (z similar to 5-0.5) and both were abruptly quenched similar to 5 Gyr ago (z similar to 0.5). The predominance of intermediate age populations in And XVI makes it qualitatively different from faint companions of the MW and clearly not a pre-reionization fossil. Neither And II nor And XVI appears to have a clear analog among MW companions, and the degree of similarity in the SFHs of And II and And XVI is not seen among comparably faint-luminous pairs of MW satellites. These findings provide hints that satellite galaxy evolution may vary substantially among hosts of similar stellar mass. Although comparably deep observations of more M31 satellites are needed to further explore this hypothesis, our results underline the need for caution when interpreting satellite galaxies of an individual system in a broader cosmological context.

Original languageEnglish
Article number24
Number of pages6
JournalAstrophysical Journal
Volume789
Issue number1
DOIs
Publication statusPublished - 1 Jul 2014

Keywords

  • galaxies: dwarf
  • galaxies: individual (And II, And XVI)
  • Galaxy: evolution
  • Galaxy: formation
  • Local Group
  • DWARF SPHEROIDAL GALAXIES
  • HUBBLE-SPACE-TELESCOPE
  • LOCAL GROUP
  • WFPC2 OBSERVATIONS
  • REIONIZATION
  • KINEMATICS
  • COMPANIONS
  • ABUNDANCES
  • EVOLUTION
  • DISK

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