Post on 13-Jan-2016
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Numerical Simulations of Galaxy Formation in a LCDM Universe
Mario G. AbadiObservatorio 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
●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
LCDM Universe
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
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
The Formation and Evolution of a Disk Galaxy
Luminous GalaxyRadius ~ 20 kpc
Dark Matter HaloVirial Radius ~ 300 kpc
Luminous Stellar HaloVirial Radius ~ 300 kpc
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)
All Stars
Spheroid
Thick Disk
Thin Disk
Dynamical Decomposition
The Formation and Evolution of a Disk Galaxy
Disk vs Halo Formation
• 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
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)
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)
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
The Inner Milky Way
Inner bright components: spheroid (or bulge), thin disk and thick disk
• Infrared Milky Way image (DRIBE COBE NASA)
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)