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ASTR 5610, Majewski [SPRING 2010]. Lecture Notes

ASTR 5610 (Majewski) Lecture Notes


Summary of Formation Scenarios: The IPII/Thick Disk Origin



"Bottom-Up" Formation Scenarios: Secular Heating


Latest secular heating process, growing in popularity, is radial migration of stars, in which, through resonant scattering by transient spiral structure, stars in the disk can change their mean orbital radii (e.g., Schonrich & Binney 2009a,b).

Process may be enhanced by bar (Minchev & Famaey 2010).

These models precit chemical, spatial and chemical trends that mimic what is seen for the thin/thick disks.


"Bottom-Up" Formation Scenarios: Violent Heating


Note different versions of this model:
  1. Stars getted heated from a pre-existing thin disk into a puffier thick disk (e.g., Quinn et al. 1993, Kazantzidis et al. 2008).

    Has to happen early on, given known old age for thick disk.

  2. Stars in the thick disk ARE the stars from the accreted body. Should show chemistry of a dSph-like galaxy (e.g., Abadi et al. 2003).

  3. Thick disk stars formed in situ from chaotic mergers of gas-rich dwarf galaxies that prompts star formation before and during the mergers (Brook et al. 2004, 2005, 2007).

    Thin disk forms after the merging phase dies down.


"Top-Down" Formation Scenarios



Summary of Formation Scenarios: The Milky Way

We may now summarize what we have learned about the presently known correlated properties of Galactic stellar populations

Do this in two ways:

The first shows the age/chemistry/star formation/population trends a la the Hodge box for the Milky Way:

From Majewski in Globular Clusters, eds. Martinez-Roger et al.
The second shows the age/dynamics/star formation/population trends:

From Majewski in Globular Clusters, eds. Martinez-Roger et al.
We note that these trends are specific to the Milky Way.

As we have seen among the dwarf galaxies in the Local Group -- galaxies seem to have individual histories that are partly driven by stochastic events, for example

Large surveys of:

hold the promise of huge advances in knowledge of galaxy evolution.
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All material copyright © 2003,2006 Steven R. Majewski. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 551 and Astronomy 5610 at the University of Virginia.