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Cosmological Galaxy Formation
The merging history of dark halos dominates
galaxy formation.

• Spiral galaxies merging of small,
• gas-rich substructures.

• Elliptical Galaxies merging of
• equal-mass substructures
• (Toomre Toomre 1972).

Spiral Galaxies Elliptical Galaxies
(Moore 2000)
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Angular Momentum and Galaxy Formation
(dOnghia, Hetznecker, Burkert)
Angular momentum j plays an important role in
disk galaxy formation
Infall into the inner regions
central starburst

• Low j

formation of galactic bulges and central black
holes
self-regulated star formation
Infall into galactic disk

• High j

j determines
Models of elliptical galaxy formation by major
mergers require a reasonable scenario for the
formation of disk galaxies.
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Simple Model of Galactic Disk Formation
Basic assumptions (Fall Efstathiou 80, Mo, Mao
White 98, Navarro Steinmetz 00)

• Initially the gas has the same specific angular
  momentum as
• the dark halo.

• Dark halos have a universal mean spin parameter

If angular momentum would be conserved, the size
distribution of galactic disks would be in
agreement with observations.
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The Cosmological Angular Momentum Problem
Prediction of the simple model
Disks retained about half the available angular
momentum.
However
(Navarro et al. 2000)
Simulated disk galaxies have scale radii that are
a factor of 10 smaller than observed
bulges instead of disks
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The Angular Momentum Distribution of Bulgeless
Spirals

• The angular momentum distribution of 20
  bulge-less spirals has been
• investigated, taking into account beam
  smearing.

(Burkert 2000 van den Bosch, Burkert Swaters
2001)
The specific angular momentum is conserved during
gas infall.
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Correlation between Angular momentum and Baryon
Fraction
There exists a surprisingly strong correlation
between and the disk mass fraction
Simple explanation
The disks either have a very small baryon
fraction or a very large specific angular
momentum.
(Burkert 2003)
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The Importance of Major Mergers

• The rotation of galaxies has long been
  discussed to result from
• gravitational torques (Hoyle 49 Peebles 69).

• High-resolution simulations find no
• steady increase of angular momentum
• with time as predicted for tidal torques
• (Vitvitska et al. 02).

• Major mergers increase

• Minor mergers dont change
• or even decrease

(Vitvitska et al.02)
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The Major Merger Problem
Major mergers are required to produce large
galactic disks.
(dOnghia Burkert, astro-ph/0402504)
bulgeless disks
(van den Bosch, Burkert Swaters 01)
minor mergers
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The Major Merger Problem
Major mergers are required to produce large
galactic disks.
(dOnghia Burkert, astro-ph/0402504)
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The Physics of Major Mergers
Spin parameter evolution during major mergers
(Hetznecker Burkert 04)
Even for major mergers there exists an angular
momentum problem!
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The Universal Angular Momentum Distribution

• Universal specific angular momentum distribution
  (Bullock et al. 00)

If angular momentum is conserved, the diskss
surface density profiles depend on
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The Predicted Surface Density Distribution
(Bullock 00, Burkert 04)
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The Specific Angular Momentum Distribution of
Bulgeless Disks
The angular momentum distribution is not in
agreement with cosmological predictions.
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Conclusions

• The average spin parameter of dark matter halos,
  corrected for
• unrelaxed major mergers is

• This is in good agreement with the TF-relation,
  if gas does not
• lose specific angular momentum during infall.

• Bulges form naturally from low-angular momentum
  gas, predicted
• to exist in cosmological models.

• If rotation curve fits indicate
  a small baryon fraction
• in bulge-less
  disk galaxies.

Substantial gas loss or inefficient cooling
(Binney 04)
Selective gas loss of preferentially low-angular
momentum gas could help to explain the origin of
exponential, bulgeless disks.
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