andreas burkert max-planck institute (mpe, garching) observatory university (munich) elena...
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Andreas Burkert
Max-Planck Institute (MPE, Garching)Observatory University (Munich)
Elena D’Onghia
Observatory University (Munich)
with
Understanding the formation of disk galaxiesis linked to understanding the origin of its angular momentum
General Theory (Fall & Efstathiou 1980):
Gas had the same specific angular momentum of dark matter halos today
Infalling gas conserves its specificangular momentum (Mestel 1963)
Angular momentum origins from tidal torques
Galactic disks with correct sizes!!!!!
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GM
EJ
Tidal torques impart angular momentum to dark matter halos
Spin parameter
Energy
Mass
hierarchical structure formation +General Theory
Galactic disks with correct sizes!!!!!
VIRd RR
SEMI-ANALYTIC MODELS
However hydrodynamical N-body simulations of diskFormation in CDM yield disks too small
The Angular Momentum Catastrophe of the gas !!
Navarro & Steinmetz 2000Abadi et al. 2003
D´Onghia, Murante & Burkert 2004, in preparation
Simulations show that galaxies are built up by merging of baryonic subclump rather than smooth accretion of gas. Much of the gas cools at the centre of subhalos and spirals toward the centre of parent halo, tranferring its orbital angular momentum to the dark matter
Better fits to real disks if Stellar FEEDBACKis included (Sommer-Larsen et al. 2003; Abadi et al. 2003)
Too dense and too massive bulges than real galaxies!!
Haloes that have had recent major mergers have largerSpin values!
Vitvitska, Klypin et al. 2002, ApJ, 581, 79904.0 6.05.0
We focus on this question:
Is the halo merging history playing a role in building small disks?
STRATEGY
We build up a set of CDM only simulations exploring thespin parameter of halos formed through various Merging history (we use Gadget code)
We identify the last major merger
Bulge/(Bulge+Disk)
Spin parameter at z=0
For each halo:
virvirVMR
J
2'
D´Onghia & Burkert, ApJL submittedastro-ph/0402504
31.0' in BBS sample of bulgeless galaxies
estimated for disks based on 1000 Sb-Sdm galaxies (de Jong & Lacey 2000)36.0
Net Result: halos dominated by minor merger accretion from z=3 to z=0acquired by tidal torques only 2% of the angular momentum for theirrotational support, whereas bulgeless galaxies acquired 6-7%
POSSIBLE SOLUTIONS?
Modification to the nature of the dark matter?Warm dark matter or Self-Interacting dark matter ? NO
Feedback from early structure formation , e.g. from smallsublumps before they merge?
However, feedback processes are unlikely to providethe additional specific angular momentum for bulgelessgalaxies
Hard to form bulgeless galaxies