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Galaxy Formation. Kravtsov (U.Chicago) D. Ceverino (NMSU). O. Valenzuela (U.Washington) G. Rhee (UNLV) F. Governato, T.Quinn, G.Stinson (U.Washington) J.Wadsley (McMaster, Canada). Hydrodynamic simulations of galaxies Rotation Curves and ISM of Dwarf Galaxies.

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Galaxy Formation

  • Kravtsov (U.Chicago)

  • D. Ceverino (NMSU)

O. Valenzuela (U.Washington)

G. Rhee (UNLV)

F. Governato, T.Quinn, G.Stinson (U.Washington)

J.Wadsley (McMaster, Canada)

Numerical simulations: recent progress

  • Stellar Disk and Bulge:

  • is there a thin disk? Is bulge too massive?

  • Angular momentum

  • Tully-Fisher relation

  • Feedback

  • How gas gets to the disk?

  • Mbaryons/Mhalo ratio



Robertson et al. 2004

(50.000 DM particles)

Hydrodynamical simulations of galaxy formation in a cosmological context.

Abadi et al 2003

(40.000 DM particles)

A lcdm galaxy at z 0 governato et al 04
A LCDM galaxy at z=0Governato et al 04


Age > 10 Gyr

Age < 10 Gyr

Disk Bulge + Stellar Halo

Only Stars are shown (brighter colors for younger ages) boxes 40 kpc across

Increasing Resolution Conserves Angular Momentum in Disks

100.000 DM

10.000 DM

4000 DM

If DM+stellar component not collisionless:

Massive halo particles exchange E and J with disk particles

---> disks heat and lose angular momentum

Angular momentum of Stellar Disks

increases with resolution.

Galaxies still too concentrated

Abadi et al. 2003

Governato et al. 2004

(see also Robertson 05 Okamoto 05)


Due to sufficient resolution 300pc disks

form with the right angular momentum

High Spin Halo


Vc =170Km/sec

Low Spin Halo


Vc =70Km/sec

Credits: Governato

Galaxies too concentrated. B/D 1:3 or higher.


3 10^12 solar masses

8 10^11 solar masses

Abadi et al 03

Governato et al. 04

Peak velocity higher than in the real Milky Way. No realistic feedback yet!

Total Mass 3e12 MsolSpin Parameter = 0.035

Vrot Max 270 Km/sec

Formation time z = 0.75

Last major merger z=3

Frame size ~ 200 Kpc

The Feedback and satellites:

Red: stars

Blue: gas

No Feedback.

UV+SN Feedback

How gas gets to the disk
How gas gets to the disk

  • The old picture is wrong: do not even think about spherical accretion and shocking to virial temperature

  • Still not clear what fraction of gas comes with satellites and what comes with filaments

Credits: Kravtsov 100pc resolution Z=4

100 kpc scale

Gas density

1 Mpc scale




40pc resolution. Mvir(z=0)=1.e12Msun. Ndm=400K



Isolated galaxies
Isolated galaxies

  • Observations

  • Simulations

Simon etal 04: NGC 4605 Vmax =100km/s

-- Usual problems with NFW.

-- Disk is important: normal M/LR=1 M/LK= 0.5


Simon etal 04 NGC 4605

Changes in PA and inclination in central 1kpc are consistent with a weak bar


DDO 47:

Vmax = 80km/s

Distance = 4Mpc

HI is very lumpy

Stellar light does not align with HI


  • A large fraction of dwarf Galaxies in the central 1kpc has a maximal disk with expected stellar population (judging by colors).

  • Signs of a weak bar are frequent.

  • ISM is very clumpy.

Cosmological Simulations: feeback, 300pc resolution …

LMC HI distribution Venn+Stavely Smith 2003)

Multiphase ISM is nicely reproduced

Governato 2004

Valenzuela et al 05


Stars: phase-on

Isolated Galaxy:

NFW halo 1-2M particles

Exponential disk 200K particles

Gas 100K

Resolution 50-100 pc

Star formation, feedback ….

Two simulations:

dwarf: 60km/s

M33-type: 120km/s



Hot Gas

T=1e5 K

Cold Gas





Hot Gas

T=1e5 K

Cold Gas



Rotation Curves:

Cold and Hot gas

Little difference

Circular Velocity

Gas Rotation

Asymmetric drift (aka random motions) cannot help to explain why gas rotates too slow

Rms Velocities < 20km/s

Another simulation: dwarf 5

Resolution: 60pc

Cold gas


Valenzuela, Rhee, Klypin, Governato et al. 2005

Models of NGC3109 and NGC6822



Gas rms velocity

Cold Gas density in the central 2kpc region:

Clear signs of multiphase medium


Cold/Hot Gas: density

Cold Gas:velocity



NGC 6822

Magellanic-type dwarf irregular

0.5Mpc from Milky Way


  • -In dwarf galaxies gas does not rotates fast enough: Vgas < Vcirc

  • -Non-circular velocities are not large enough to account for the difference

  • -Pressure support from 1e5K gas is one of key ingredients

    Core is ‘observed’ where there is a real cusp.

Structure of the ISM at z= 0.5

(several 10^6 particles per halo, gas clouds resolved down to 10^5 solar masses)

Hot Halo (Blue)

Ram Pressure Stripping

Gas Rich Satellites

High Velocity Clouds

Cold Gas in Disks

Bars in galaxies:

Simulations with ART and Gadget.

50-100pc resolution

200K disk particles

2M dm particles.

Dt =1e4 yrs