Elena D’Onghia
Max-Planck Institute (MPE, Garching)
Observatory University (Munich)
with
Andreas Burkert
Observatory University (Munich)
Understanding the formation of disk galaxies
is linked to understanding the origin of its
angular momentum
General Theory (Fall & Efstathiou 1980):
Angular momentum origins from tidal torques
Gas had the same specific angular
momentum of dark matter halos today
Infalling gas conserves its specific
angular momentum (Mestel 1963)
Galactic disks with correct sizes!!!!!
SEMI-ANALYTIC MODELS
General Theory
+
hierarchical structure formation
Tidal torques impart angular momentum to dark matter halos
1/ 2
| J || E |

5/ 2
GM
Spin parameter
Energy
Mass
Rd  RVIR
Galactic disks with correct sizes!!!!!
However hydrodynamical N-body simulations of disk
Formation in CDM yield disks too small
Navarro & Steinmetz 2000
Abadi et al. 2003
The Angular Momentum Catastrophe of the gas !!
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 FEEDBACK
is included (Sommer-Larsen et al. 2003; Abadi et al. 2003)
Too dense and too massive bulges than real galaxies!!
   0.04
  0.5  0.6
Vitvitska, Klypin et al. 2002, ApJ, 581, 799
Haloes that have had recent major mergers have larger
Spin values!
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 the
spin parameter of halos formed through various
Merging history (we use Gadget code)
For each halo:
We identify the last major merger
Bulge/(Bulge+Disk)
Spin parameter at z=0
' 
J
2 MRvirVvir
D´Onghia & Burkert, ApJL submitted
astro-ph/0402504
  '  0.31
in BBS sample of bulgeless galaxies
   0.36
estimated for disks based on 1000 Sb-Sdm galaxies (de Jong & Lacey 2000)
Net Result: halos dominated by minor merger accretion from z=3 to z=0
acquired by tidal torques only 2% of the angular momentum for their
rotational support, whereas bulgeless galaxies acquired 6-7%
Hard to form bulgeless galaxies
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 small
sublumps before they merge?
However, feedback processes are unlikely to provide
the additional specific angular momentum for bulgeless
galaxies