Formation, vertex deviation, and age of the Milky Way's bulge: Input from a cosmological simulation with a late-forming bar

Victor P. Debattista*, Oscar A. Gonzalez, Robyn E. Sanderson, Kareem El-Badry, Shea Garrison-Kimmel, Andrew Wetzel, Claude André Faucher-Giguère, Philip F. Hopkins

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

We present the late-time evolution of m12m, a cosmological simulation of a Milky Way-like galaxy from the FIRE project. The simulation forms a bar after redshift z = 0.2. We show that the evolution of the model exhibits behaviours typical of kinematic fractionation, with a bar weaker in older populations, an X-shape traced by the younger, metal-rich populations, and a prominent X-shape in the edge-on mean metallicity map. Because of the late formation of the bar in m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate the bulge, at a level higher than is observed at high latitudes in the Milky Way, implying that its bar cannot have formed as late as in m12m. We also study the model's vertex deviation of the velocity ellipsoid as a function of stellar metallicity and age in the equivalent of Baade's Window. The formation of the bar leads to a non-zero vertex deviation. We find that metal-rich stars have a large vertex deviation (∼40), which becomes negligible for metal-poor stars, a trend also found in the Milky Way, despite not matching in detail. We demonstrate that the vertex deviation also varies with stellar age and is large for stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertex deviation. When we exclude stars that have been accreted, the vertex deviation is not significantly changed, demonstrating that the observed variation of vertex deviation with metallicity is not necessarily due to an accreted population.

Original languageEnglish (US)
Pages (from-to)5073-5085
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume485
Issue number4
DOIs
StatePublished - Mar 13 2019

Fingerprint

apexes
deviation
stars
simulation
metallicity
metal
FIRE (climatology)
metals
Milky Way Galaxy
fractionation
kinematics
ellipsoids
polar regions
trends

Keywords

  • Galaxy: bulge
  • Galaxy: evolution
  • Galaxy: formation
  • Galaxy: kinematics and dynamics
  • Galaxy: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Debattista, V. P., Gonzalez, O. A., Sanderson, R. E., El-Badry, K., Garrison-Kimmel, S., Wetzel, A., ... Hopkins, P. F. (2019). Formation, vertex deviation, and age of the Milky Way's bulge: Input from a cosmological simulation with a late-forming bar. Monthly Notices of the Royal Astronomical Society, 485(4), 5073-5085. https://doi.org/10.1093/mnras/stz746
Debattista, Victor P. ; Gonzalez, Oscar A. ; Sanderson, Robyn E. ; El-Badry, Kareem ; Garrison-Kimmel, Shea ; Wetzel, Andrew ; Faucher-Giguère, Claude André ; Hopkins, Philip F. / Formation, vertex deviation, and age of the Milky Way's bulge : Input from a cosmological simulation with a late-forming bar. In: Monthly Notices of the Royal Astronomical Society. 2019 ; Vol. 485, No. 4. pp. 5073-5085.
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abstract = "We present the late-time evolution of m12m, a cosmological simulation of a Milky Way-like galaxy from the FIRE project. The simulation forms a bar after redshift z = 0.2. We show that the evolution of the model exhibits behaviours typical of kinematic fractionation, with a bar weaker in older populations, an X-shape traced by the younger, metal-rich populations, and a prominent X-shape in the edge-on mean metallicity map. Because of the late formation of the bar in m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate the bulge, at a level higher than is observed at high latitudes in the Milky Way, implying that its bar cannot have formed as late as in m12m. We also study the model's vertex deviation of the velocity ellipsoid as a function of stellar metallicity and age in the equivalent of Baade's Window. The formation of the bar leads to a non-zero vertex deviation. We find that metal-rich stars have a large vertex deviation (∼40◦), which becomes negligible for metal-poor stars, a trend also found in the Milky Way, despite not matching in detail. We demonstrate that the vertex deviation also varies with stellar age and is large for stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertex deviation. When we exclude stars that have been accreted, the vertex deviation is not significantly changed, demonstrating that the observed variation of vertex deviation with metallicity is not necessarily due to an accreted population.",
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Formation, vertex deviation, and age of the Milky Way's bulge : Input from a cosmological simulation with a late-forming bar. / Debattista, Victor P.; Gonzalez, Oscar A.; Sanderson, Robyn E.; El-Badry, Kareem; Garrison-Kimmel, Shea; Wetzel, Andrew; Faucher-Giguère, Claude André; Hopkins, Philip F.

In: Monthly Notices of the Royal Astronomical Society, Vol. 485, No. 4, 13.03.2019, p. 5073-5085.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Formation, vertex deviation, and age of the Milky Way's bulge

T2 - Input from a cosmological simulation with a late-forming bar

AU - Debattista, Victor P.

AU - Gonzalez, Oscar A.

AU - Sanderson, Robyn E.

AU - El-Badry, Kareem

AU - Garrison-Kimmel, Shea

AU - Wetzel, Andrew

AU - Faucher-Giguère, Claude André

AU - Hopkins, Philip F.

PY - 2019/3/13

Y1 - 2019/3/13

N2 - We present the late-time evolution of m12m, a cosmological simulation of a Milky Way-like galaxy from the FIRE project. The simulation forms a bar after redshift z = 0.2. We show that the evolution of the model exhibits behaviours typical of kinematic fractionation, with a bar weaker in older populations, an X-shape traced by the younger, metal-rich populations, and a prominent X-shape in the edge-on mean metallicity map. Because of the late formation of the bar in m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate the bulge, at a level higher than is observed at high latitudes in the Milky Way, implying that its bar cannot have formed as late as in m12m. We also study the model's vertex deviation of the velocity ellipsoid as a function of stellar metallicity and age in the equivalent of Baade's Window. The formation of the bar leads to a non-zero vertex deviation. We find that metal-rich stars have a large vertex deviation (∼40◦), which becomes negligible for metal-poor stars, a trend also found in the Milky Way, despite not matching in detail. We demonstrate that the vertex deviation also varies with stellar age and is large for stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertex deviation. When we exclude stars that have been accreted, the vertex deviation is not significantly changed, demonstrating that the observed variation of vertex deviation with metallicity is not necessarily due to an accreted population.

AB - We present the late-time evolution of m12m, a cosmological simulation of a Milky Way-like galaxy from the FIRE project. The simulation forms a bar after redshift z = 0.2. We show that the evolution of the model exhibits behaviours typical of kinematic fractionation, with a bar weaker in older populations, an X-shape traced by the younger, metal-rich populations, and a prominent X-shape in the edge-on mean metallicity map. Because of the late formation of the bar in m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate the bulge, at a level higher than is observed at high latitudes in the Milky Way, implying that its bar cannot have formed as late as in m12m. We also study the model's vertex deviation of the velocity ellipsoid as a function of stellar metallicity and age in the equivalent of Baade's Window. The formation of the bar leads to a non-zero vertex deviation. We find that metal-rich stars have a large vertex deviation (∼40◦), which becomes negligible for metal-poor stars, a trend also found in the Milky Way, despite not matching in detail. We demonstrate that the vertex deviation also varies with stellar age and is large for stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertex deviation. When we exclude stars that have been accreted, the vertex deviation is not significantly changed, demonstrating that the observed variation of vertex deviation with metallicity is not necessarily due to an accreted population.

KW - Galaxy: bulge

KW - Galaxy: evolution

KW - Galaxy: formation

KW - Galaxy: kinematics and dynamics

KW - Galaxy: structure

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