Comparing m31 and milky way satellites: The extended star formation histories of andromeda

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

doi:10.1088/0004-637X/789/1/24

Comparing m31 and milky way satellites: The extended star formation histories of andromeda

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

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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 _/M⊙) ∼ 6.7) and Andromeda XVI (And XVI; M_V = -7.5; log(M _/M⊙) ∼ 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.

Original language	English (US)
Article number	24
Journal	Astrophysical Journal
Volume	789
Issue number	1
DOIs	https://doi.org/10.1088/0004-637X/789/1/24
State	Published - Jul 1 2014

Keywords

Galaxies: dwarf
Galaxies: individual (And II, And XVI)
Galaxy: evolution
Galaxy: formation
Local Group

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Weisz, D. R., Skillman, E. D., Hidalgo, S. L., Monelli, M., Dolphin, A. E., McConnachie, A., Bernard, E. J., Gallart, C., Aparicio, A., Boylan-Kolchin, M., Cassisi, S., Cole, A. A., Ferguson, H. C., Irwin, M., Martin, N. F., Mayer, L., McQuinn, K. B. W., Navarro, J. F., & Stetson, P. B. (2014). Comparing m31 and milky way satellites: The extended star formation histories of andromeda. Astrophysical Journal, 789(1), Article 24. https://doi.org/10.1088/0004-637X/789/1/24

Weisz, DR, Skillman, ED, Hidalgo, SL, Monelli, M, Dolphin, AE, McConnachie, A, Bernard, EJ, Gallart, C, Aparicio, A, Boylan-Kolchin, M, Cassisi, S, Cole, AA, Ferguson, HC, Irwin, M, Martin, NF, Mayer, L, McQuinn, KBW, Navarro, JF & Stetson, PB 2014, 'Comparing m31 and milky way satellites: The extended star formation histories of andromeda', Astrophysical Journal, vol. 789, no. 1, 24. https://doi.org/10.1088/0004-637X/789/1/24

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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; MV = -12.0; log(M /M⊙) ∼ 6.7) and Andromeda XVI (And XVI; MV = -7.5; log(M /M⊙) ∼ 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.",

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

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T2 - The extended star formation histories of andromeda

AU - Weisz, Daniel R.

AU - Skillman, Evan D.

AU - Hidalgo, Sebastian L.

AU - Monelli, Matteo

AU - Dolphin, Andrew E.

AU - McConnachie, Alan

AU - Bernard, Edouard J.

AU - Gallart, Carme

AU - Aparicio, Antonio

AU - Boylan-Kolchin, Michael

AU - Cassisi, Santi

AU - Cole, Andrew A.

AU - Ferguson, Henry C.

AU - Irwin, Mike

AU - Martin, Nicolas F.

AU - Mayer, Lucio

AU - McQuinn, Kristen B.W.

AU - Navarro, Julio F.

AU - Stetson, Peter B.

PY - 2014/7/1

Y1 - 2014/7/1

N2 - 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; MV = -12.0; log(M /M⊙) ∼ 6.7) and Andromeda XVI (And XVI; MV = -7.5; log(M /M⊙) ∼ 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.

AB - 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; MV = -12.0; log(M /M⊙) ∼ 6.7) and Andromeda XVI (And XVI; MV = -7.5; log(M /M⊙) ∼ 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.

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KW - Galaxies: individual (And II, And XVI)

KW - Galaxy: evolution

KW - Galaxy: formation

KW - Local Group

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Comparing m31 and milky way satellites: The extended star formation histories of andromeda

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