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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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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