The Milky Way in the Context of Barred Galaxies: Dark Matter and (Chemo-) Dynamics
Final Report Abstract
Galaxies are basic building blocks of the Universe. Their formation and evolution from tiny initial fluctuations to their presently observed states is one of the most important current problems in astrophysics. To study galaxy evolution we have here followed the approach of investigating the fossil evidence in nearby galaxies, as encoded in the motions, ages and element abundances of the stars in these galaxies. In particular we have focussed on large spiral galaxies such as our Milky Way and the nearby Andromeda galaxy M31, which are part of a class of galaxies in which a bar structure in the disk was important for driving gas into the central regions and enhancing star formation. However, these galaxies also grow and change through accretion of smaller galaxies, early-on in the case of the Milky Way, but only a few gigayears ago in M31. The element abundances of stars are highest in the inner disks of these galaxies where the gas from which they formed has been enriched by many previous generations of stars. We used hydrodynamical simulations to determine the mass distribution in this region, and the rotation rate of the bar which together determine the orbits of the stars. Then, with a newly developed method we showed that the high-abundance stars in M31 flare not only in the barred bulge as also seen in the Milky Way, but also further out in its disk. Together with the flat abundance gradients this is likely a signature of the recently accreted satellite that has heated and mixed M31’s disk. To conduct similar studies for more distant barred galaxies, we developed and tested the Schwarzschild method for modelling spatially resolved two-dimensional kinematics, abundances and age information for the stars in these galaxies, with applications currently on-going.
Publications
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Deprojection of external barred galaxies from photometry. Monthly Notices of the Royal Astronomical Society, 508(4), 6209-6222.
Tahmasebzadeh, Behzad; Zhu, Ling; Shen, Juntai; Gerhard, Ortwin & Qin, Yujing
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Unravelling stellar populations in the Andromeda Galaxy. Astronomy & Astrophysics, 647, A131.
Gajda, Grzegorz; Gerhard, Ortwin; Blaña, Matías; Zhu, Ling; Shen, Juntai; Saglia, Roberto P. & Bender, Ralf
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Gas Dynamics in the Galaxy: Total Mass Distribution and the Bar Pattern Speed. The Astrophysical Journal, 925(1), 71.
Li, Zhi; Shen, Juntai; Gerhard, Ortwin & Clarke, Jonathan P.
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Large-scale Hydrodynamical Shocks as the Smoking-gun Evidence for a Bar in M31. The Astrophysical Journal, 933(2), 233.
Feng, Zi-Xuan; Li, Zhi; Shen, Juntai; Gerhard, Ortwin; Saglia, R. P. & Blaña, Matias
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Orbit-superposition Dynamical Modeling of Barred Galaxies. The Astrophysical Journal, 941(2), 109.
Tahmasebzadeh, Behzad; Zhu, Ling; Shen, Juntai; Gerhard, Ortwin & Ven, Glenn van de
