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Star Formation at High Redshift: Observational Progress and Theoretical Perspectives Romeel Davé movie by B. Oppenheimer
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Cosmic SF History Madau et al 1996 Hopkins & Beacom 2006 x10 from z=1-0 ~flat z=4-1 rising to z~4 - Systematics >~x2 - Sample overlap?
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Breaking down cosmic SF Bursty or quiescent? How important are mergers? How much is obscured? Stellar mass growth vs. SFR? Is hi-z SF systematically different?
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Main Sequence of Galaxy Formation SFR ~ M * 0.7-0.9, scatter 0.3 dex. Evolves down independently of M * SFR quiescent, not burst, dominated Noeske etal 07 z~0.2-1.1 Daddi etal 07 z~1.4-2.5 Elbaz etal 07 z~0.8-1.2 Labbe etal 10 z~7
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SFR from mergers? Close pairs: 3:1 mergers Morphological: <30% global SF in interacting BUT– Asymmetry: ~50% z~1 SF in “mergers” Non-interacting galaxies dominate SFRD Robaina et al 2009 Jogee et al 2009 Shi+09
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Bouwens+09 Obscured star formation Most SF obscured; peaks at z~2. LIRGs/ULIRGs dominate to z~1,2…but don’t interpret as local ULIRG analogs! Dust production SF to disks Seymour+09
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SFR vs. dM * /dt dM*/dt << SFR (+IMF) at z~2-3 Completeness? (Reddy+09) Is SFR at z~2-3 fundamentally different? RD 08 Wilkins+ 09
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How Do We Understand All this? Computers !
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A Not-totally-wrong Story for Star-forming Galaxies Cold flows Smooth accretion Regulation by galactic outflows The Galaxy-IGM connection Truncation by mergers/AGN
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Cold mode accretion Cold flows dominategas infall for ALL star- forming galaxies. Hot halos for >10 12 M Infall from IGM disk R vir R cool Dekel+ 09 z=2, AMR At z>~1-2, flowspenetrate hot halo. At low-z, flowsbreak up intoclouds (HVCs?) z=2, 10 12 M haloz=1, 10 13 M halo Keres+ 09
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Cold Mode -- in every hydro sim ever done
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SFR tracks accretion SFGs at all masses, epochs process accreted gas into stars on t<<t H Keres+09
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Accretion is Smooth Accretion is ~smooth (& filamentary). Mergers subdominant. Keres etal 09
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Generic predictions Tight SFR-M * relation, evolves indep of M * Mergers/bursts sub- dominant in SFRD. Disturbed morphology due to rapid accretion Early galaxies grow rapidly. … too rapidly! Need feedback. RD 08 Bournaud+ 07: Unstable disk sim Data: Bouwens+06 z~6 RD et al 06
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Feedback Regulates SF Halo mass function, scaled by b/m. Baldry+ 08
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Cosmic Feedback Cycle
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Outflows: Observations & Implications Common at z~1+: Σ SFR >>0.1 M ⊙ /kpc 2 Δv ISM ~ hundreds km/s Local SBs, z~1 SFG: v w v circ Momentum-driven winds? If so, mass loading factor η 1/v circ Note: Similar scalings may arise from other physical mechanisms. M82: Spitzer 8μ Martin 2005 100
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Correct (early) evolution of cosmic SFR IGM enriched to match CIV, OVI absorbers Mass-metallicity with right slope & scaller High gas fractions in low-M galaxies DLA kinematics w/enough wide systems Non-grav entropy in intracluster gas … all from including one simple scaling of outflows with galaxy mass. Such Outflows Yield…
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Mass in outflows >> Mass in stars Winds recycle a lot; recycled wind accretion dominates at z<~1. Many baryons blown out of even large halos Outflows keep galaxies gas rich (not poor). MZR set by balance of inflows and outflows, not gas processing rate … Some Surprising Implications M wind ~ 3 M * Median N recyc ~3 BDO & RD 08
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Z~M 1/3 The “Equilibrium” MZR Model z=2 Finlator&RD 08 Z ~ y M * /M acc ~ y (1+ ) -1 If v w >v esc, constant constant Z. For v w <v esc, 0, Z y. Produces a feature in MZR-- not seen. For mom-driven winds: ~M * -1/3 ~v c -1 Z(M * )~M * 1/3 Z gas set by an equilibrium between recent inflow and outflows.
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680 km/s 340 km/s v w ~v circ Recycling sets the GSMF Halo mass function, scaled by b/m. Baldry+ 08 t rec short; Lots of recycled wind mode t rec longer; Less recycled wind mode t rec > t hubble ; No recycled wind mode t rec irrelevant; Need to quench star formation! t rec irrelevant; Need to quench star formation!
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Galaxies as “Gas Processing Engines” Obtain gas via cold, smooth accretion Creates tight evolving M * -SFR relation. Process into stars (some) or eject into outflows (most) on a short timescale. SFR, gas content, metallicity set by balance of inflow vs outflow. Ejected material recycles, moreso in larger galaxies. Sets shape and evolution of galaxy stellar mass function.
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SFR-M * : Close but no cigar Models get right: Slope Scatter General evolution But amplitude evolution is wrong! Data has higher SFR at given M*. But wait… cold accretion sets maximum rate! RD 08 Green: Millenium SAM Red, magenta: SPH sims Blue: Data ( =0.3)
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Birthrate evolution: Huh? Discrepant during the peak dusty SF epoch. Something different? Calibrations? IMF? Gonzalez+ 10 Simulations RD 08
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Summary 3 regimes of cosmic SFH: Early growth (z>4), rapid phase (1<z<4), late decline (z<1) Dominated by fairly smooth, filamentary cold accretion. Mergers & bursts subdominant. Dust embedded SF peaks @ z~2. Before that, less dust; after, SF morphology change? Generally, trends well explained by Cold mode accretion, smooth & filamentary Outflows that eject more mass from small gals. Mismatch between SFR and M* evolution, both vs. data and theory?
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Diff recycling governs GSMF Without wind mode, GSMF~halo MF (scaled). Wind recycling boosts higher M* galaxies, flattens GSMF. Once t recyc > t Hubble, reverts to steep slope, modulated by outflows (vzw shallower since ~1/v circ ).
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Halo baryon content Winds drive lots of baryons out of halos. Big galaxies lose baryons early. MW-like halo today has lost ~½ baryons Peak SF “efficiency” @ 10 13 M . Qualitatively similar to observations.
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Winds recycle! M winds >> M stars wind ~ 0.2 b ejected ~ 0.5 b Compare: * ~ 0.08 b Median # ejections: 3 Turnaround radius ~100 physical kpc high-z: Enrich IGM low-z: Halo fountains Median t recyc ~ 1 Gyr
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Constraints from IGM enrichment Outflows are the only way to enrich IGM z~2-4 CIV absorbers very constraining; favors momentum-driven wind scalings: v w ~v circ, ~v circ -1. wind speed mass loading Too few metals in IGM IGM too hot Diffuse IGM unenriched Too few metals produced Momentum-driven wind scalings! Metallicity Overdensity Oppenheimer & RD 2006 Oppenheimer & RD 2008 Oppenheimer & RD 2009a,b
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Gas content f gas (M * ) strongly dependent on outflows. M-D winds keep low- mass galaxies gas rich by suppressing SF. Strong outflows make galaxies gas rich, not gas poor. Galaxies are the antithesis of closed boxes: They process gas as supplied.
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Z~M 1/3 Mass-Metallicity Relation z=2 Finlator&RD 08 Conventional thinking: Z gas reflects stage of processing Galaxies lose metals based on . NO! Why? Outflows are greedy & destructive: They don’t share their energy -- they blow holes! Analytic3D simulation
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“Wind mode” accretion
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Differential Recycling t recycling goes inversely with mass 680 km/s 340 km/s v w ~v circ
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Luminosity functions z~6: Large SF suppression. Rapid consumption must eject gas. M acc = M * +M outflow SFR (1+ ) -1 z~2-4: Const ~2+ ~ v c -1 ~1.7 z=0: Faint end slope ~1.3; less steep! (bright end?…fugly) Data: Bouwens etel 06 Models: =0.3, 8 =0.9 RD, Finlator, Oppenheimer 06
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DLA Kinematics: Outflows? Wide separation ( v>v rot ) DLAs hard to produce; protogalactic clump infall fails (eg Pontzen etal). Momentum-drive winds puff out gas, produces wide- separation systems. Prochaska & Wolfe 01 KS test prob no winds, 8e-5 constant winds, 0.037 MD winds, 0.51 No winds Mom-driven windsConstant winds S. Hong, Katz, RD etal, in prep
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Feedback Tomography Background sources observe outflows in action. Tough now, but will become routine at z~2+ in 30m era. COS enables at z<1 Also possible in emission around galaxies. The next frontier of observational galaxy formation!
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