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How well do we understand outflows and accretion on cosmic scales?

How well do we understand outflows and accretion on cosmic scales?. Romeel Davé. Galactic Outflows. Cold mode accretion is dense & filamentary  Need bouncer feedback to prevent overcooling: Outflows

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How well do we understand outflows and accretion on cosmic scales?

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  1. How well do we understand outflows and accretion on cosmic scales? Romeel Davé

  2. Galactic Outflows • Cold mode accretion is dense & filamentary  Need bouncer feedback to prevent overcooling: Outflows • Test outflow scaling relations by comparing hydro simulations to outflow-related observables, e.g.: • IGM enrichment [Oppenheimer & RD 06] • Early galaxies & overcooling [RD, Finlator, Oppenheimer 07] • Mass-metallicity relation [Finlator & RD 07] • DLA kinematics [S. Hong, Katz etal in prep] • ICM metals & energy [RD etal in prep] • A single wind scaling relation matches all these!

  3. Quantifying Outflows Martin 2005 Erb etal 06 z~2 SFG’s • Outflows rare locally, but probably the norm at z>~2. • Two basic parameters: • Outflow velocity: vw • Mass loading factor: h • Martin 05, Rupke etal 05: Starbursts show vwvcirc. • Murray etal 05: Such a scaling arises in momentum-driven winds: vwvc, h1/vc • Implement into Gadget-2, Monte Carlo ejection of particles, vc computed from Mgal using on-the-fly finder. M82 MIPS Engelbracht etal log h

  4. How unique is this outflow model? Erb et al 2006 • Short answer: Not terribly. • Key features that seem necessary to match data: • Winds eject mass & metals from ALL galaxies, not just dwarfs. • Small galaxies expel a higher fraction of their accreted gas. • Outflow rate » star formation rate @ early epochs. • M-D scalings work, but feel free to invent your own… Log Wind kinetic/Potential

  5. How do outflows set galaxy properties? z=2 Momentum- driven scalings Mass outflow rate out of halo Red: input scalings Black: actual Constant vw,h • Key insight: Accreted gas is processed quickly Inflow ≈ Outflow + SFR. •  SFR = Inflow/(1+h). This inflow equilibrium relation broadly governs galaxy properties (e.g. SFH, Z, fgas). • e.g. fgas is set by h(M*). If this doesn’t vary with z, then fgas(M*) doesn’t vary with z [as observed]. • Energetics arguments for outflows are not relevant. Outflows don’t share energy, they blow holes and leave. • Bottom line: h is key! vwind irrelevant, beyond >vesc.

  6. What does this mean for outflow physics? • Unclear; approx scalings could in principle be generated from momentum or energy driven winds. • SN-driven sims usually fail to remove much gas mass from the ISM (Mac Low & Ferrara; Teyssier’s talk). • In principle, lots of momentum available from light and stellar winds to drive gas out, but coupling unclear. • Need ISM sims of momentum-driven winds! • Much to be done on feedback… What about accretion? log h

  7. The M*-SFR Relation Daddi etal 07 z~1.4-2.5 • Gas accretionstar formation • M*-SFR constrains SFH form: • Observations of SFGs (z~0-2): • M*SFR0.7-0.9at all z. • Small scatter (<0.3 dex) around “main sequence” of SFGs. • Evolution is M*-independent. Elbaz etal 07 z~0.8-1.2 Noeske etal 07 z~0.2-1.1

  8. M*-SFR vs. Models • Green: Millenium SAM • Red, magenta: SPH • Blue: Data (s=0.3) • Slope <~unity?  • Scatter small?  • Evolves independent of M*?  • Evolves at observed rate? ×

  9. Models Data 1011M 1010.5 log SFR (Mo/yr) 1010 109.5 Star Formation Activity Parameter (i.e. fraction of Hubble time required to form M* at current SFR). • Models: asf~1 at all z. • Cold accretion  similar forms of SFH at all M*. • Observed: asf(z) evolves strongly. Oops! • Possibilities: • Simulated SFH wrong? • Measurements wrong? • Or…

  10. IMF wrong?[insert Stacy McGaugh MOND dance] • Need less M* formed per unit high-mass SF • Conservatively, SFR/M* should be reduced by ~x3 at z=2, and ~x2 at z=1: This would yield unevolving asf. • Larson (98,05): IMF today has Mchar≈0.5 M. High-z ISM hotter  Mchar higher. • “Evolving Kroupa” IMF (0.1-100 M): dN/dlogMM-0.3 for M<Mchar. dN/dlogMM-1.3 for M>Mchar. Mchar=0.5(1+z)2 M from PEGASE modeling

  11. Evolving IMF • No effect on high-mass SF/feedback/ metals; only detectable in M* accumulation rate. • SFR down by ~×(1+z) • Fardal etal: Reconciling fossil light (rK, EBL) and integrated cosmic SFH“Paunchy” IMF. • Perez-Gonzalez etal (IRAC): M* to z~4. dM*/dt < SFR @z>2. • Not crazy…

  12. Summary • It is possible to constrain basic outflow parameters across cosmic time by comparing hydro sims to galaxy SFR and ZIGM data. • Best matches are for scalings reminiscent of momentum-driven winds, but actual physics of wind propagation unknown. • Mass loading factor h is key: SFRZ(1+h)-1. • Accretion appears to be reasonably well understood, but at face value the evolution of SFR-M* doesn’t agree. • An IMF that is more bottom-light at high-z is an explanation that seems equally as (un)likely as any of the alternatives, and may be favored from fossil light considerations.

  13. Simulated SFH wrong? • At z~2, observed asf~0.2. • Problem: Can’t reconcile asf~0.2 with other data, let alone models. • Bursts? (tip of iceberg) • M*-SFR tight; Lower SFRs would’ve been seen. • Delayed SF? (strong early feedback) • asf~0.2 implies z~2 systems began SF at z~2.3! Plus, low scatter for 1.4<z<2.5. • Unseen passive galaxies? (downsizing) • Mass-selected samples do not see enough passive galaxies; sBzK selects dominant population at z~2. • All seem dubious (besides being inconsistent with models).

  14. Measurements wrong? (Systematics) • Need to lower SF / raise M* by ~x3-5. • Raising M* generically hard: Unless stars put out a LOT less red light than locally. [note: Maraston vs. BC03 goes wrong way] • Something else mimicking SF? • AGN: Possible, but would have to be strange to exactly mimic tight M*SFR. • PAH emission: Rest-8m dominated by PAHs, so perhaps PAH emission per unit SF much stronger at high z. • Can’t be ruled out, but would require dramatic differences vs locally calibrated relations. Such differences not seen locally even in extreme systems.

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