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Star Formation at High Redshift: Observational Progress and Theoretical Perspectives

Romeel Davé. movie by B. Oppenheimer. Star Formation at High Redshift: Observational Progress and Theoretical Perspectives. Cosmic SF History. Madau et al 1996. x10 from z=1-0. ~flat z=4-1. rising to z~4. - Systematics >~x2 - Sample overlap?. Hopkins & Beacom 2006.

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Star Formation at High Redshift: Observational Progress and Theoretical Perspectives

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  1. Romeel Davé movie by B. Oppenheimer Star Formation at High Redshift:Observational Progress and Theoretical Perspectives

  2. Cosmic SF History Madau et al 1996 x10 from z=1-0 ~flat z=4-1 rising to z~4 - Systematics >~x2 - Sample overlap? Hopkins & Beacom 2006

  3. 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?

  4. Main Sequence of Galaxy Formation Elbaz etal 07 z~0.8-1.2 • SFR ~ M*0.7-0.9, scatter 0.3 dex. • Evolves down independently of M* • SFR quiescent, not burst, dominated Daddi etal 07 z~1.4-2.5 Labbe etal 10 z~7 Noeske etal 07 z~0.2-1.1

  5. SFR from mergers? • Close pairs: <10% global SF in >3:1 mergers • Morphological: <30% global SF in interacting • BUT– Asymmetry: ~50% z~1 SF in “mergers” • Non-interacting galaxies dominate SFRD Jogee et al 2009 Shi+09 Robaina et al 2009

  6. 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! SF to disks Dust production Seymour+09 Bouwens+09

  7. SFR vs. dM*/dt Wilkins+ 09 • dM*/dt << SFR (+IMF) at z~2-3 • Completeness? (Reddy+09) • Is SFR at z~2-3 fundamentally different? RD 08

  8. How Do We Understand All this? • Computers!

  9. 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

  10. Cold mode accretion Rvir Infall from IGM Rcool disk • Cold flows dominate gas infall for ALL star-forming galaxies. • Hot halos for >1012 M • At z>~1-2, flows penetrate hot halo. • At low-z, flows break up into clouds (HVCs?) z=2, 1012M halo z=1, 1013M halo Dekel+ 09 z=2, AMR Keres+ 09

  11. Cold Mode -- in every hydro sim ever done

  12. SFR tracks accretion • SFGs at all masses, epochs process accreted gas into stars on t<<tH Keres+09

  13. Accretion is Smooth • Accretion is ~smooth (& filamentary). • Mergers subdominant. Keres etal 09

  14. 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. Data: Bouwens+06 z~6 Bournaud+ 07: Unstable disk sim RD et al 06 RD 08

  15. Feedback Regulates SF Halo mass function, scaled by Wb/Wm. Quenching UV Photons Outflows Baldry+ 08

  16. Cosmic Feedback Cycle

  17. Outflows: Observations & Implications Common at z~1+: ΣSFR>>0.1 M⊙/kpc2 ΔvISM~ hundreds km/s Local SBs, z~1 SFG: vwvcircMomentum-driven winds? If so, mass loading factor η1/vcirc Note: Similar scalings may arise from other physical mechanisms. M82: Spitzer 8μ Martin 2005 100

  18. 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…

  19. 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 Mwind ~ 3 M* Median Nrecyc~3 BDO & RD 08

  20. z=2 Finlator&RD 08 The “Equilibrium” MZR Model   • Z ~ y M*/Macc ~ y (1+h)-1 • If vw>vesc, constant h constant Z. For vw<vesc, h0, Zy. Produces a feature in MZR-- not seen. • For mom-driven winds: h~M*-1/3~vc-1Z(M*)~M*1/3 • Zgas set by an equilibrium between recent inflow and outflows. Z~M1/3

  21. Recycling sets the GSMF Halo mass function, scaled by Wb/Wm. 680 km/s vw~vcirc    trec > thubble; No recycled wind mode trec longer; Less recycled wind mode trec short; Lots of recycled wind mode 340 km/s trec irrelevant; Need to quench  star formation! Baldry+ 08

  22. 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.

  23. SFR-M*: Close but no cigar RD 08 • 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! • Green: Millenium SAM • Red, magenta: SPH sims • Blue: Data (=0.3)‏

  24. Birthrate evolution: Huh? Gonzalez+ 10 • Discrepant during the peak dusty SF epoch. • Something different? Calibrations? IMF? Simulations RD 08

  25. 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?

  26. Diff recycling governs GSMF • Without wind mode, GSMF~halo MF (scaled). • Wind recycling boosts higher M* galaxies, flattens GSMF. • Once trecyc > tHubble, reverts to steep slope, modulated by outflows (vzw shallower since h~1/vcirc).

  27. 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” @ 1013M. • Qualitatively similar to observations.

  28. Winds recycle! • Mwinds >> Mstars • Wwind ~ 0.2 Wb • Wejected ~ 0.5 Wb • Compare: W* ~ 0.08 Wb • Median # ejections: 3 • Turnaround radius ~100 physical kpc • high-z: Enrich IGM • low-z: Halo fountains • Median trecyc ~ 1 Gyr

  29. Constraints from IGM enrichment IGM too hot Too few metals produced Momentum-driven wind scalings! Too few metals in IGM wind speed Diffuse IGM unenriched mass loading • Outflows are the only way to enrich IGM • z~2-4 CIV absorbers very constraining; favors momentum-driven wind scalings: vw~vcirc, h~vcirc-1. Metallicity Overdensity Oppenheimer & RD 2006 Oppenheimer & RD 2008 Oppenheimer & RD 2009a,b

  30. Gas content • fgas(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.

  31. z=2 Finlator&RD 08 Mass-Metallicity Relation • Conventional thinking: • Zgas reflects stage of processing • Galaxies lose metals based on F. • NO! Why? Outflows are greedy & destructive: • They don’t share their energy -- they blow holes! Z~M1/3 Analytic 3D simulation

  32. “Wind mode” accretion

  33. Differential Recycling • trecycling goes inversely with mass 680 km/s vw~vcirc 340 km/s

  34. Luminosity functions Data: Bouwens etel 06 Models: =0.3, 8=0.9 RD, Finlator, Oppenheimer 06 • z~6: Large SF suppression. • Rapid consumption  must eject gas. • Macc = M*+Moutflow SFR (1+h)-1 • z~2-4: • Const ha~2+ • h ~ vc-1a~1.7 • z=0: Faint end slope a~1.3; less steep! • (bright end?…fugly)   

  35. Constant winds Mom-driven winds No winds no winds, 8e-5 constant winds, 0.037 MD winds, 0.51 DLA Kinematics: Outflows? • Wide separation (v>vrot) DLAs hard to produce; protogalactic clump infall fails (eg Pontzen etal). • Momentum-drive winds puff out gas, produces wide-separation systems. S. Hong, Katz, RD etal, in prep Prochaska & Wolfe 01 KS test prob

  36. 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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