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 language | English (US) |
|---|---|
| Pages (from-to) | 5073-5085 |
| Number of pages | 13 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 485 |
| Issue number | 4 |
| DOIs | |
| State | Published - Mar 13 2019 |
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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
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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 journal › Article
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
UR - http://www.scopus.com/inward/record.url?scp=85064450103&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85064450103&partnerID=8YFLogxK
U2 - 10.1093/mnras/stz746
DO - 10.1093/mnras/stz746
M3 - Article
AN - SCOPUS:85064450103
VL - 485
SP - 5073
EP - 5085
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -