Numerical Simulations of Galaxy Formation in a LCDM Universe

1. Mario G. Abadi Observatorio Astronómico De La Universidad Nacional De Córdoba CONICET, Argentina Collaborators: Julio Navarro: University of Victoria, Canada Matthias Steinmetz: Astrophysikalisches Institute, Postdam, Germany Vincent Eke: University of Durham, United Kingdom Andres Meza: Universidad de Chile, Santiago, Chile Amina Helmi: Kapteyn Astronomical Institute, Groningen, Netherlands Numerical Simulations of Galaxy Formation in a LCDM Universe

2. LCDM Universe • WMAP and LSS results have established LCDM model as the new paradigm of hierarchical structure formation • Low mass density but flat scenario • Fully specified by the following cosmological parameters: • Constituents 70% dark energy, 26% dark matter and 4% baryons • Amplitude of mass fluctuation in spheres of 8 Mpc/h is given by RMS=0.9 and a Hubble´s constant h=0.7with no tilt in the initial power spectrum • Success in LS (>1mpc) closer to linear regime

3. Galaxy Formation • Observed disk at odds with ”natural” trends of hierarchical models • Difficult to reconcile the early collapse and eventful merging history with dynamical clues which point to a smooth assembly of disks • Fragility of disks to rapid fluctuations of the gravitational potential such as those stirred by mergers or satellite accretion events • Dominant, cold, thin, stellar disks points to a histoty of mass accretion where major mergers have player a minor role • Age of oldest disk stars used to estimate the epoch of the last major merger (14 gyrs in the solar neighborhood) • Milky Way’s thick disk has its origin in an early thin disk of velocity and size comparable to today’s but “thickened” by the accretion of a satellite

4. Numerical Simulations • Initial conditions given by the lambda CDM model • Astrophysics: gravitation, hydrodynamics, radiative cooling, star formation, feedback and metals • Initially only dark matter and gas particles • Gas particles transformed in star particles • 8 simulations finished with M~ 1-2x10^11 solar masses and N~0.6-1.8x10^5 star particles inside 20 kpc @ z=0

5. The Formation and Evolution of a Disk Galaxy

6. Luminous GalaxyRadius ~ 20 kpc

7. Dark Matter HaloVirial Radius ~ 300 kpc

8. Luminous Stellar HaloVirial Radius ~ 300 kpc

9. Observational and Theoretical Approach • Observational • Photometric (luminosity, isophotes, surface brightness profile decomposition, bulge to disk ratio, fundamental plane, colors, star formation) • Kinematics (gas and stars rotation curves, velocity maps, Tully fisher and Faber Jackson relation) • Theoretical • Dynamics (dark matter, gas and stars properties, evolution, mass distribution, velocity support, dynamical decomposition, in-situ vs accretion, origin of different components)

10. All Stars

11. Spheroid

12. Thick Disk

13. Thin Disk

14. Dynamical Decomposition

15. The Formation and Evolution of a Disk Galaxy

16. Disk Young (90%) + old (10%) Rotational velocity supported Outcome of a smooth dissipative deposition (and transformation into stars) of gas cooling more or less continuously off the intergalactic medium Eggen Lynden-bell & Sandage (1962) Correlations between metallicity and kinematics of 221 stars in the solar neighborhood Halo Old (predate the last major merger) Velocity dispersion supported Build up over an extended period of time through a number of early mergers Searle & Zinn (1978) Wide range of metal abundances independent of radius for 177 red gigants in 19 globular clusters Disk vs Halo Formation

17. Halo Evidence of Accretion Events • Tidal streams of the Sagittarius dSph galaxy (Ibata el al. 1994) • Substructure in the galactic halo (Helmi et al. 1999) • Giant stream of metal-rich giants around Andromeda (Ibata el al. 2001)

18. Disk Evidence of Accretion Events • Monoceros ring in the outer Galaxy (Yanny et al. 2003) • Canis Major dwarf (Martin et al. 2004) • Arcturus stream (Navarro et al. 2004) • Debris from omega Cen parent galaxy in the solar neighborhood (Meza et al. 2005) • Substructure in the Galactic disk (Helmi et al. 2005)

19. Conclusions • Galaxy componets in cosmological context: spheroid, thin disk, thick disk, but also stellar halo, satellites and dark matter halo • Simulated galaxies resemble observed galaxies, surface brightness, colors, etc • Different implementation of astrophysical effects in order to avoid efficient star formation at early times and massive spheroid and stellar halos • Stellar halos form from mergers • Disk form from dissipative collapse • There is growing evidence that the hierarchical models are correct

20. The Inner Milky Way Inner bright components: spheroid (or bulge), thin disk and thick disk • Infrared Milky Way image (DRIBE COBE NASA)

21. The Outer Milky Way Inner bright components: spheroid (or bulge), thin disk and thick disk Outer faint components: satellites and stellar halo both difficult to detect in other galaxies Outer dark components: dark matter halo and substructure • Infrared Milky Way image (DRIBE COBE NASA)