Galaxy Formation: An Overview

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Review talk by Prof. Romeel Dave' at the SuperJEDI Conference, July 2013

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Galaxy Formation: An Overview

  1. 1. Our Universe, Age 380,000 years Galaxy Formation Cosmology Star Formation Stellar Evolution Chemical Enrichment Dark Matter Black Holes ? Hubble GOODS field
  2. 2. Hierarchical Galaxy Formation • Galaxy formation = Halo growth + Gas accretion + Feedback • Halo growth: Cosmology • Gas Accretion: Gravity + cooling • Feedback: ??? Gravitational instability: Cosmic Web From Max Tegmark
  3. 3. Infall from IGM disk Rvir Rcool Dekel+ 09 z=2, AMR How Does Gas Accrete Into Galaxies? • Hot mode: Heated to Tvir; ~spherical, slow. • Cold mode: Filamentary, rapid, smooth, T ~ 104 K. • Transition mass: Hot halo when Mhalo >~ 1012 M. White & Rees 1978Gabor, RD+11
  4. 4. Feedback Regulates SFFeedback Regulates SF Baldry+ 08 Halo mass function, scaled by Ωb/Ωm. Baldry+ 08
  5. 5. Milky Way Schematic
  6. 6. Multiwavelength M31
  7. 7. Multiwavelength Antennae
  8. 8. Gas Processing Factories η/(1+η) ★ 1/(1+η) αΖ Mgrav ζMgrav SFR = ζMgrav/(1+η)(1-αZ)
  9. 9. Equilibrium Relations  Finlator+RD 08
  10. 10. Scaling Relations & Scatter • First order: Scaling rel’ns – Mgrav ∼ fb Mhalo 1.1 (1+z)2.25 That gas comes in “lumps” is, to first order, irrelevant. • Second order: Scatter – Mergers, environment, satel- lites, etc are 2nd order effects. – Accreting a lump higher fgas & SFR, lower Z. Mannucci+10 
  11. 11. Preventive Feedback: Photo-ionization, AGN, gravity, winds, …? Stars can form RD+11
  12. 12. Intuition from the Equilibrium Scenario
  13. 13. Main Sequence Galaxies as “Gas Processing Engines” • Obtain gas via cold, smooth accretion – Creates tight evolving M*-SFR relation. • Process some gas into stars – Produces cosmic evolution of SF, main seq. • Ejects most gas into outflows – SFR, gas content, metallicity set by balance of inflow vs outflow. • Ejected material recycles – Critical at low-z, sets e.g. stellar mass fcn shape.
  14. 14. Cold accretion dominates • Star formation is supply-limited. • Mergers are a small contribution to accretion. Keres+09
  15. 15. Fundamental driver: Halo growth  e.g. 1012 M halo  … at z=0, Min = 6 M/yr  … at z=2, Min = 80 M/yr Prediction: A given mass galaxy forms stars faster at high redshifts. Dekel et al 2009   from D. Elbaz Observations
  16. 16. Quenching star formation • Use SAM intuition to make “red and dead” galaxies: Heat halo gas when fhot>0.6 • Produces correct: – Red sequence – Bright-end luminosity/mass fcn – Does not change faint end • Physics uncertain, but it likely has something to do with hot halo gas! Gabor, RD+11
  17. 17. “Holistic” Approaches: SAMs and Sims• Semi-analytic models (SAMs) parameterize baryon dynamics, constrain via observables. + Fast; tunable; builds on N-body. - Non-unique; builds in assumptions. • Hydrodynamic simulations directly track gas. + Physics more robust; convergence tests possible - Slow; limited dynamic range; subgrid physics parameters • Compare to widest possible range of data: “holistic”. • Sims develop physical insight; SAMs explore,
  18. 18. Our Cosmological Hydro Code N-body plus hydro: - Gravity using Tree-PM - Gas dynamics using EC-SPH - Cooling (H,He,metal) Parameterized subgrid physics: - Star formation - Galactic outflows - (Quenching feedback) Typical simulation parameters: - Spatial resolution: ~1-5 kpc (Kennicutt Law scale) - Mass resolution: ~106-8 M. - Box size: ~10-100 Mpc. - Evolve from linear regime (z>>100) to today.
  19. 19. IGM enrichment: Outflow TracerIGM enrichment: Outflow Tracerwindspeed mass loading Too few metals in IGM IGM too hot Diffuse IGM unenriched Too few metals produced Momentum-driven wind scalings! Oppenheimer & RD 2006 Oppenheimer & RD 2008 Oppenheimer & RD 2009a,b Lyman alpha forest Metal absorbers (mostly CIV)

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