Comparing M31 and Milky Way satellites: The extended star formation histories of Andromeda II and Andromeda XVI
- Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN (United States)
- Instituto de Astrofísica de Canarias. Vía Láctea s/n., E-38200 La Laguna, Tenerife, Canary Islands (Spain)
- Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
- Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
- Astronomy Department, University of Maryland, College Park, MD (United States)
- INAF-Osservatorio Astronomico di Collurania, Teramo (Italy)
- School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania (Australia)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Observatoire astronomique de Strasbourg, Universit de Strasbourg, CNRS, UMR 7550, 11 rue de l'Universit, F-67000 Strasbourg (France)
- Institut für Theoretische Physik, University of Zurich, Zürich (Switzerland)
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{sub V} = –12.0; log(M {sub *}/M {sub ☉}) ∼ 6.7) and Andromeda XVI (And XVI; M{sub V} = –7.5; log(M {sub *}/M {sub ☉}) ∼ 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 ∼ 5-0.5) and both were abruptly quenched ∼5 Gyr ago (z ∼ 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.
- OSTI ID:
- 22356521
- Journal Information:
- Astrophysical Journal, Vol. 789, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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