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

1. Our Universe,
Age 380,000 years
Galaxy
Formation
Cosmology Star
Formation
Stellar
Evolution
Chemical
Enrichment
Dark
Matter
Black
Holes
?
Hubble GOODS field

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. 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. Feedback Regulates SFFeedback Regulates SF
Baldry+ 08
Halo mass function,
scaled by Ωb/Ωm.
Baldry+ 08

6. Milky Way
Schematic

7. Multiwavelength M31

8. Multiwavelength Antennae

9. Gas Processing Factories
η/(1+η)
★
1/(1+η)
αΖ
Mgrav
ζMgrav
SFR = ζMgrav/(1+η)(1-αZ)

10. Equilibrium Relations
 Finlator+RD 08

11. 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


12. Preventive Feedback:
Photo-ionization, AGN,
gravity, winds, …?
Stars can form
RD+11

13. Intuition from the Equilibrium Scenario

14. 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.

15. Cold accretion dominates
• Star formation is supply-limited.
• Mergers are a small contribution to accretion.
Keres+09

16. 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

17. 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

18. “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,

19. 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.

20. 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)