1. The Origin and Structure of Elliptical Galaxies
Structure formation by hierarchical
merging.
Spiral galaxies: merging of small,
gas-rich substructures.
Elliptical Galaxies: merging of
equal-mass substructures
(Toomre & Toomre 1972).
Spiral galaxies Elliptical Galaxies
(Moore 2000)

2. The Origin and Structure of Elliptical Galaxies
Collisionless merger
Gas-rich merger
( Hernquist 92, 93, Naab & Burkert 93)
( Bekki 99; Mihos & Hernquist 96;
Springel et al. 05)
( Naab & Burkert )

3. Testing the Merger Hypothesis
The merger hypothesis has been investigated numerically
(Gerhard 81;Barnes 92; Hernquist 92,93; Mihos & Hernquist 93,96)
Remnants
spheroidal and follow a de Vaucouleurs law
slowly rotating and anisotropic v
(Binney 82)
Anisotropy: v

4. Violent Relaxation of Collisionless Particle Systems
CDM
simulation
DM density profile
NFW
(Hetznecker & Burkert)

5. Isophotal Shapes
More insight requires a more detailed investigation of
departures from pure elliptical isophotes
Boxy and disky ellipticals:
boxy:
disky:
(Bender 1987)

6. Disky and Boxy Ellipticals
Boxy and disky ellipticals form two distinct groups with different kinematical properties (Bender et al. 88,89).
Violent relaxation cannot
explain these observations.
Can the merger scenario
explain this dichotomy?
boxy
disky

7. Initial Conditions High-resolution merger simulations with mass ratios
1:1, 2:1, 3:1, and 4:1 (Naab & Burkert ).
Spirals consist of disk, bulge and dark halo.
face on
Edge on

8. Anisotropy of Merger Remnants
versus v
Equal mass mergers are anisotropic and boxy
3:1 and 4:1 remnants are fast, isotropic rotators and disky
2:1 remnants show intermediate properties
1:1
2:1
3:1
4:1
Anisotropy and isophotal shape depends on the mass ratio.

9. The Frequency of Boxy and Disky Ellipticals
The ratio of boxy-to-disky ellipticals should not depend on luminosity
Khochfar & Burkert 03

10. The Frequency of Boxy and Disky Ellipticals
The ratio of boxy-to-disky ellipticals should not depend on luminosity
observations
theory
Khochfar & Burkert 03

11. Spheroidal and Mixed Mergers
The merger fraction between galaxies of different morphologies
depends strongly on redshift and mass (Khochfar & Burkert 03).
E-E
E-E 1 2 3 4
-22
-20
-18 z
Massive boxy ellipticals might result from E-E mergers.

12. Spheroidal Merger Simulations
E-E merger simulation 1
S-S
3:1
E-E -1 -2
(Naab, Khochfar & Burkert 05)
E-E merger remnants are boxy and very anisotropic even
for large mass ratios of 3:1 or 4:1.

13. More than 20% gas accretion
Assumption 1:
E-E mergers
boxy
Assumption 2:
More than 20% gas accretion
disky BH
feedback
Assumption 3:
Star formation suppressed
for
(Naab, Khochfar & Burkert 05)

14. Energetic Feedback
by Central Black Hole
(Springel et al. 05)

15. Kinematics of Merger Remnants
The main difference between disky, unequal mass merger remnants and
boxy, equal-mass mergers is not their anisotropy but their rotation.
(Burkert & Naab 05)

16. Kinematics of Merger Remnants
(Burkert & Naab 05)

17. SAURON Integral Field Kinematics
(De Zeeuw et al. 92)
M 31
Intrinsic properties from axisymmetric three-integral
Schwarzschild models.

18. SAURON Integral Field Kinematics
(Cappellari et al. astro-ph/ )
boxy
disky
0.6
0.4
0.2
Disky ellipticals are anisotropic with high ellipticities.
Boxy ellipticals are isotropic and round.

19. boxy
disky
0.6
0.4
0.2
(Burkert & Naab 06)

21. What‘s about early-type mergers?
prolate
oblate

22. Summary The major merger scenario can explain the origin of
fast rotating, disk ellipticals
equal-mass merger
slowly rotating, boxy ellipticals
unequal-mass merger
All ellipticals show a large spread in anisotropy.
Ellipticals with assembled from early-type mergers.
Central BH feedback suppresses star formation for
Major mergers are not consistent with the structure of ellipticals
as predicted from Schwarzschild models.

23. The End

24. The Merging History of the Universe
Extended Press-Schechter theory (Kauffmann & White 1993; Khochfar &
Burkert 2000, 2001, 2002) Frequency of minor or major mergers.
Redshift dependence
Final mass dependence N z
Disky : Boxy = 5 : 3, independent of z and M

25. The Skewness of Elliptical Galaxies
Bender, Saglia & Gerhard (94) studied the line-of-sight velocity
distribution of elliptical galaxies.
They detected small deviations from a Gaussian distribution that
can be characterized by Gauss-Hermite-functions.
> 0: shift to negative v
< 0: shift to positive v

26. Rotation of Merger Remnantsv
versus
1:1
2:1
3:1
4:1
Equal mass mergers
rotate slowly.
3:1 and 4:1 remnants rotate fast.
2:1 remnants show intermediate rotation
Rotation depends on the mass ratio.

27. The Skewness of Elliptical Galaxies
Bender, Saglia & Gerhard (94) studied the line-of-sight velocity
distribution of elliptical galaxies.
> 0: shift to negative v
< 0: shift to positive v
Ellipticals show a distinct
correlation between their
local and 3 h v
(Pickney et al. 03)

28. The Skewness of Elliptical Galaxies
Bender, Saglia & Gerhard (94) studied the line-of-sight velocity
distribution of elliptical galaxies.
> 0: shift to negative v
< 0: shift to positive v
Ellipticals show a distinct
correlation between their
local and 3 h v
(Bender et al. 94)

29. The Skewness of Collisionless Merger Remnants
2 dimensional analysis of the LOSVD on a grid superimposed on the merger remnant.
Collisionless merger
major axis
v > 0
v < 0 v

30. The Role of Gas in Major Mergers

31. Gas-rich Merger Simulations
Formation of a gaseous disk.

32. Evidence for Gaseous Mergers
2 dimensional analysis of the LOSVD on a grid superimposed on the merger remnant.
Gaseous merger
v > 0
v < 0
major axis
v > 0
v < 0 v

33. The Early-Type Angular Momentum Problem
Faint ellipticals rotate faster than the fastest simulated remnants. v
Gas cannot solve this problem (Naab & Burkert 04)
Angular momentum problem
for early-type galaxies.
(Cretton, Naab, Burkert, Rix 2000)

34. Conclusions Elliptical galaxies formed by major mergers.
Kinematics and isophotal shape of merger remnants is determined by their mass ratio:
1:1-2: anisotropic + boxy
3:1-4: fast rotating + disky.
Low luminosity ellipticals experienced substantial gas inflow
after the last major merger disky 2-component
systems with a disk embedded in a spheroidal component
Their LOS velocity distribution also indicates that the progenitors
were gas-rich spiral galaxies.
Very luminous, boxy ellipticals might have formed from
gas-poor, early-type mergers.

35. Statistics of Boxy and Disky Ellipticals
The CDM-model predicts an overabundance of disky ellipticals
which should be independent of mass.
Disky : Boxy = 5 : 3
log I
This ratio agrees with observations of
intermediate- and low mass ellipticals.
Properties of ellipticals with
Boxy
More massive than disk galaxies
High metallicities and enhanced
(Mehlert et al. 00,03)
log
Formation redshift:

36. Projection Effects
Projection effects lead to a large scatter but do not change the result. v v v v

38. The central stellar disk in NGC 3623
(de Zeeuw et al. 02) I
(Naab & Burkert)
3:1 merger

39. Central Properties of Merger Remnants
Sauron data
M32
with gas
3:1 merger simulation I

40. Luminous ellipticals did not form through
Additional Problems
Luminous ellipticals:
are more massive than disk galaxies
formed at high redshifts
have high metallicities
(Mehlert et al. 03, Thomas et al. 03)
Luminous ellipticals did not form through
major mergers

41. The End

42. Problem 2: Anisotropy
1:1
2:1
3:1
4:1
(Naab & Burkert 2003)

43. Problem 1: Isophotal Shapes
20% bulge
10% bulge
no bulge
with gas
(Naab, Burkert 2003)

44. Projection effects
Projection effects lead to a large scatter but do not change the result. v v v v
Violent relaxation alone cannot explain this dichotomy.

45. Spiral 1:1 Merger
E-E Merger
Gas-rich 3:1 merger

46. Elliptical Galaxies The de Vaucouleurs law: Cluster galaxies
Collaborators: Th. Naab, S. Khochfar, R. Jesseit, M. Wetzstein
The de Vaucouleurs law:
Cluster galaxies
Spheroidal stellar systems.
No star formation.

47. Elliptical Galaxies The Sersic Law Cluster galaxies
Collaborators: Th. Naab, S. Khochfar, Roland Jesseit
The Sersic Law
Cluster galaxies
Spheroidal stellar systems.
No star formation. n
-12
-24 1 10
Graham et al. 02
Trujillo & Burkert 04

48. Kinematical Properties
Massive elliptical galaxies are anisotropic, triaxial systems
(e.g. Binney 82; de Zeeuw 97; Cretton et al. 00)
Ellipticity distribution
Anisotropy v
(Binney & Tremaine 87)
(Binney 82) v
Anisotropy:

49. The Cosmological Angular Momentum Problem
Major mergers are required to produce extended galactic disks.
(D‘Onghia & Burkert, astro-ph/ )
bulgeless disks
(van den Bosch
et al. 01)
minor mergers
The merging history of Es cannot be studied in a cosmological context.

50. The Formation of
Elliptical Galaxies

51. Collisionless Merger Simulations
Equal-mass merger
Analysis of the remnant based on the same methods as
used by observers.