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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. and Gonzalez, Oscar A. and Sanderson, Robyn E. and El-Badry, Kareem and Garrison-Kimmel, Shea and Wetzel, Andrew and Faucher-Giguère, Claude-André and Hopkins, Philip F. (2018) Formation, vertex deviation and age of the Milky Way's bulge: input from a cosmological simulation with a late-forming bar. . (Unpublished)

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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, which becomes negligible for metal-poor stars, a trend also found in the Milky Way. 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.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Sanderson, Robyn E.0000-0003-3939-3297
El-Badry, Kareem0000-0002-6871-1752
Garrison-Kimmel, Shea0000-0002-4655-8128
Wetzel, Andrew0000-0003-0603-8942
Faucher-Giguère, Claude-André0000-0002-4900-6628
Hopkins, Philip F.0000-0003-3729-1684
Additional Information:V.P.D. was supported by STFC Consolidated grant ST/M000877/1. R.E.S. was supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under grant AST-1400989. Support for S.G.K. was provided by NASA through Einstein Postdoctoral Fellowship grant PF5-160136 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. A.W. was supported by NASA through grants HST-GO-14734 and HST-AR-15057 from STScI. Support for P.F.H. was provided by an Alfred P. Sloan Research Fellowship, NSF Collaborative Research Grant #1715847 and CAREER grant #1455342. K.E.mB. acknowledges support from a Berkeley graduate fellowship, a Hellman award for graduate study, and an NSF Graduate Research Fellowship. Numerical calculations were run on the Caltech compute cluster "Wheeler," allocations from XSEDE TG-AST130039 and PRAC NSF.1713353 supported by the NSF, NASA HEC SMD-16-7592, and the High Performance Computing at Los Alamos National Labs. CAFG was supported by NSF through grants AST-1412836, AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant NNX15AB22G, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/M000877/1
NSF Astronomy and Astrophysics FellowshipAST-1400989
NASA Einstein FellowshipPF5-160136
Alfred P. Sloan FoundationUNSPECIFIED
University of California, BerkeleyUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:Galaxy: bulge - Galaxy: evolution - Galaxy: formation - Galaxy: kinematics and dynamics - Galaxy: structure
Record Number:CaltechAUTHORS:20190206-105548856
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92716
Deposited By: George Porter
Deposited On:08 Feb 2019 20:41
Last Modified:08 Feb 2019 20:41

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