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!!!!!

2/5

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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