How well do we understand outflows and accretion on cosmic scales

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
Erb etal 06 z2 SFGs

• Outflows rare locally, but probably the norm at
  zgt2.
• 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?

• 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 _at_ early
  epochs.
• M-D scalings work, but feel free to invent your
  own

Log Wind kinetic/Potential
5
How do outflows set galaxy properties?

• Key insight Accreted gas is processed quickly ?
  Inflow Outflow SFR.
• ? SFR Inflow/(1h). This inflow equilibrium
  relation broadly governs galaxy properties (e.g.
  SFH, Z, fgas).
• e.g. fgas is set by h(M). If this doesnt vary
  with z, then fgas(M) doesnt vary with z as
  observed.
• Energetics arguments for outflows are not
  relevant. Outflows dont share energy, they blow
  holes and leave.
• Bottom line h is key! vwind irrelevant, beyond
  gtvesc.

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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 Teyssiers
  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
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The M-SFR Relation
Daddi etal 07 z1.4-2.5

• Gas accretion ? star formation
• M-SFR constrains SFH form
• Observations of SFGs (z0-2)
• M?SFR0.7-0.9 at all z.
• Small scatter (lt0.3 dex) around main sequence
  of SFGs.
• Evolution is M-independent.

Elbaz etal 07 z0.8-1.2
Noeske etal 07 z0.2-1.1
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M-SFR vs. Models

• Green Millenium SAM
• Red, magenta SPH
• Blue Data (s0.3)
• Slope ltunity? ?
• Scatter small? ?
• Evolves independent of M? ?
• Evolves at observed rate?

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Star Formation Activity Parameter

• (i.e. fraction of Hubble time required to form
  M at current SFR).
• Models asf1 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

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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 z2, and x2 at z1 This would yield
  unevolving asf.
• Larson (98,05) IMF today has Mchar0.5 M?.
  High-z ISM hotter ? Mchar higher.
• Evolving Kroupa IMF (0.1-100 M?)
• dN/dlogM?M-0.3 for MltMchar.
• dN/dlogM?M-1.3 for MgtMchar.
• Mchar0.5(1z)2 M? ? from PEGASE modeling

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Evolving IMF

• No effect on high-mass SF/feedback/ metals only
  detectable in M accumulation rate.
• SFR down by (1z)
• Fardal etal Reconciling fossil light (rK, EBL)
  and integrated cosmic SFH?Paunchy IMF.
• Perez-Gonzalez etal (IRAC) M to z4. dM/dt lt
  SFR _at_zgt2.
• Not crazy

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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?(1h)-1.
• Accretion appears to be reasonably well
  understood, but at face value the evolution of
  SFR-M doesnt 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 z2, observed asf0.2.
• Problem Cant reconcile asf0.2 with other data,
  let alone models.
• Bursts? (tip of iceberg)
• M-SFR tight Lower SFRs wouldve been seen.
• Delayed SF? (strong early feedback)
• asf0.2 implies z2 systems began SF at z2.3!
  Plus, low scatter for 1.4ltzlt2.5.
• Unseen passive galaxies? (downsizing)
• Mass-selected samples do not see enough passive
  galaxies sBzK selects dominant population at
  z2.
• All seem dubious (besides being inconsistent with
  models).

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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.
• Cant be ruled out, but would require dramatic
  differences vs locally calibrated relations.
  Such differences not seen locally even in extreme
  systems.