A.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)

Galaxy Formation

• Hydrodynamic simulations of galaxies

• Rotation Curves and ISM of Dwarf Galaxies

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

Abadi et al 2003

Hydrodynamical simulations of galaxy Hydrodynamical simulations of galaxy formation in a cosmological context.formation in a cosmological context.

(50.000 DM particles)

(40.000 DM particles)

gasstars

A LCDM galaxy at z=0 Governato et al 04

Age > 10 Gyr

Age < 10 Gyr

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

Disk Bulge + Stellar Halo

N>100.000

Increasing Resolution Conserves Angular Momentum in Disks

4000 DM

10.000 DM

100.000 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 concentratedAbadi et al. 2003Governato et al. 2004(see also Robertson 05 Okamoto 05)

stars

High Spin Halo(0.05)

Vc =170Km/sec

Low Spin Halo(0.01)

Vc =70Km/sec

Due to sufficient resolution 300pc disks form with the right angular momentum

Credits: Governato

8 10^11 solar masses3 10^12 solar masses

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

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

feedback yet!

Governato et al. 04 Abadi et al 03

Governato

The Feedback and satellites:

No Feedback. UV+SN Feedback

Red: starsRed: starsBlue: gasBlue: gas

Total Mass 3e12 Msol Spin Parameter = 0.035 Vrot Max 270 Km/sec Formation time z = 0.75 Last major merger z=3 Frame size ~ 200 Kpc

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12

F.Governato: simulations with GASOLINE

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F.Governato: simulations

with GASOLINE

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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

1 Mpc scale

100 kpc scale

Tgas

Gas density

Credits: Kravtsov 100pc resolution Z=4

350kpc

Z=2.5

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

350kpc

Z=2.5

115kpc

7kpc

7kpc

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

1arcmin

Simon etal 04 NGC 4605

POSS II

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.

Observations:

LMC HI distribution Venn+Stavely Smith 2003)LMC HI distribution Venn+Stavely Smith 2003)

Cosmological Simulations: feeback, 300pc resolution …

Governato 2004Multiphase ISM is nicely reproduced

Valenzuela et al 05

Isolated Galaxy:

NFW halo 1-2M particles

Exponential disk 200K particles

Gas 100K

Resolution 50-100 pc

Star formation, feedback ….

Stars: phase-on

Two simulations:

dwarf: 60km/s

M33-type: 120km/s

Code: GASOLINE

Stars

YoungStars

T<0.5Gyrs

Cold GasT<1.5e4

Hot GasT=1e5 K

Cold GasT<1.5e4

Hot GasT=1e5 K

Stars

YoungStars

T<0.5Gyrs

• Cold gas hardly shows any traces of the bar.• Filaments and lumps of cold gas • Large bubbles filled by 105K gas• Stellar feedback feeds the multiphase ISM

Rotation Curves:

Cold and Hot gas

Little difference

Gas Rotation

Circular Velocity

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

Rms Velocities < 20km/s

Recovering total density

Another simulation: dwarf 5

Resolution: 60pc

starsCold gas

dm

baryons

Gas rms velocity

Valenzuela, Rhee, Klypin, Governato et al. 2005

Models of NGC3109 and NGC6822

Cold Gas density in the central 2kpc region:

Clear signs of multiphase medium

Cold/Hot Gas: density

Stars

Cold Gas:velocity

NGC 6822

Observations

Vcirc(total)

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.

CONCLUSIONS

Structure of the ISM at z= 0.5 (several 10^6 particles per halo, gas clouds resolved down to 10^5 solar masses)

Ram Pressure Stripping

Cold Gas in Disks

High Velocity Clouds Gas Rich Satellites

Hot Halo (Blue)

Bars in galaxies:

Simulations with ART and Gadget.

50-100pc resolution

200K disk particles

2M dm particles.

Dt =1e4 yrs