Download - Galaxy Formation: An Overview
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Our Universe,Age 380,000 years
Galaxy Formation
Cosmology StarFormation
Stellar Evolution
ChemicalEnrichment
Dark Matter
BlackHoles
?
Hubble GOODS field
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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
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InfallfromIGM
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
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Feedback Regulates SFFeedback Regulates SF
Baldry+ 08
Halo mass function, scaled by b/m.
Baldry+ 08
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Milky Way Schematic
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Multiwavelength M31
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Multiwavelength Antennae
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Gas Processing Factories
★
Mgrav
Mgrav
SFR = Mgrav/(1+)(1-Z)
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Equilibrium Relations
Finlator+RD 08
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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
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Preventive Feedback:
Photo-ionization, AGN, gravity, winds, …?
Stars can form
RD+11
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Intuition from the Equilibrium Scenario
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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.
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Cold accretion dominates
• Star formation is supply-limited.• Mergers are a small contribution to accretion.
Keres+09
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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
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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
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“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, synthesize.
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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.
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IGM enrichment: Outflow TracerIGM enrichment: Outflow Tracerw
ind
spee
d
mass loading
Too fewmetals in IGM
IGM too hot
Diffuse IGM unenriched
Too fewmetalsproduced
Momentum-driven wind scalings!
Oppenheimer & RD 2006Oppenheimer & RD 2008Oppenheimer & RD 2009a,b
Lyman alpha forest Metal absorbers(mostly CIV)