with: joop schaye leiden (as of last week) simulation provided by: tom theuns, volker springel, lars...
TRANSCRIPT
with:
Joop Schaye
Leiden (as of last week)
Simulation provided by:
Tom Theuns, Volker Springel, Lars Hernquist, Scott Kay
QSO spectra by:
T.-S. Kim, W. Sargent, M. RauchAnthony Aguirre
UC Santa Cruz
Confronting models of intergalactic enrichment with
the observations
IGM metallicity provides information on:
History of star/galaxy formation.
Formation of unobservably early stars/galaxies.
UV ionizing background.
Feedback in galaxy formation processes.
Basic question: how did the enrichment happen?
Two basic enrichment scenarios:
1. “Early” enrichment by z >> 6 galaxies.
Features:• Outflows from protogalaxies/Pop. III.
• Small wells easier to escape from.
• Low outflow velocities -> little heating.
• IGM has time to “recover.”
Model as: no effect on IGM, metals sprinkled in.
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Two basic enrichment scenarios:
2. “Late” enrichment by 2 < z < 6 galaxies.
Features:• Strong feedback during galaxy formation. • Heating of IGM.
• Supported: Observed z ~ 3 galaxies drive strong winds like low-z starbursts.
Two basic enrichment scenarios:
2. “Late” enrichment by 2 < z < 6 galaxies.
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Two basic enrichment scenarios:
2. “Late” enrichment by 2 < z < 6 galaxies.
Features:• Strong feedback during galaxy formation. • Heating of IGM.
• Supported: Observed z ~ 3 galaxies drive strong winds like low-z starbursts.
• Galaxy formation theory: strong feedback seems necessary.
• Most of cosmic star formation at z < 5.
1. Look for evolution in Z at z < 5.
2. Check temperature of gas (late enrichment should come with/in hot gas).
3. Compare amount of metals with expectations.
4. Look at spatial distribution of metals.
5. Look at abundance ratios for info. on nucleosynthetic sources.
Signatures of early vs. late in observed IGM.
All this and more can be done with:
Pixel method in brief
HI, CIV pixel optical depth pairs
19x
Correlations(see Aguirre et al. 02; Schaye et al. 03 for details)
Two approaches:
Infer metallicity from observations (using non-enriching simulations were necessary).
Generate spectra from enrichment simulations and compare optical depth ratios to those in observed spectra.
1. Metallicity inferences
Correlations
UVB model
Hydro. simulations
Metallicities
Results: Carbon metallicities from CIV
1. The carbon metallicity [C/H] is inhomogeneous and density-dependant.
(see Schaye et al. 2003)
Results: Carbon metallicities from CIV
2. The median carbon metallicity [C/H] does not evolve (for our fiducial UVB) from z~4 to z~2.
Neither does ([C/H])
Results: Carbon metallicities from CIV
2. The median carbon metallicity [C/H] does not evolve (for our fiducial UVB) from z~4 to z~2.Clearly favors enrichment at z > 4.But: there is some room for more.
Results: Carbon metallicities from CIV
3. [C/H] depends on UVB model.
But very different UVBs can be ruled out.
Gas temperature from CIII, SiIII
4. CIII/CIV, SiIII/SiIV provide thermometer.Bulk of SiIV gas at T<104.9KLittle scatter in gas temp.But some evidence for hotter gas? (< 30%)Similar results using CIII/CIV.
(see Aguirre et al. 2004)
Gas temperature from CIII, SiIII
4. CIII/CIV, SiIII/SiIV provide thermometer.Most observed metals are in photoionized, warm gas, not the collisionally ionized warm/hot gas expected from winds.
Silicon metallicities from SiIV, CIV
5. SiIV/CIV vs CIV: ratios depend on , reproduced by simulation.
[Si/C] ~ 0.25-1.5 (for diff. UVBs)No scatter in
inferred [Si/C]
(see Aguirre et al. 2004)
Adding up global C, Si abundances.
6. Lots of metals in the forest![C/H] = -2.8, [Si/H] = -2.0
Easily half of all metals at z ~ 3. Can z >> 6 enrichment suffice? Also, clusters: metallicity evolution and/or hidden metals in hot gas and low-z IGM appears to have Z ~ 0.1 Zsol!
(see Aguirre et al. 2004)
Method 2: comparing observed spectra to feedback simulations by:Theuns et al. 02 and Springel & Hernquist 03
both: Smoothed Particle Hydrodynamics (SPH) simulations with baryon particle mass ~106 Msolar.But: different feedback prescriptions.
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(see Aguirre et al. 2005)
Comparison with CIV/HI
Non-feedback/imposed metallicity: good fit.
Feedback models: too low CIV/HI.
Comparison with CIII/CIV
Non-feedback/imposed metallicity: good fit.
Feedback models: too low CIII/CIV
Problem: gas too hot, too low-density
Enriched gas at 105-107 K, -1 < < 1
But CIV/C, CIII/CIV fall at low-, high T.
Enriched low-density gas
Problem: gas too hot, too low-density
Possible rescue: metal cooling.
Comparison with CIV/HI, CIII/CIV
With cooling prescription:
Better.
Not so much.
Final problem: sims. too inhomogeneous
Independent of cooling and UVB, simulations cannot simultaneously explain multiple percentiles.
Stems from small filling factor.
0.5% of metal-rich
0.05% of metal-free
Summary and Ruminations:
Simulations cannot reproduce CIV/HI, or CIII/CIV, or
CIV distribution. (But Metal cooling needed).
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Summary and Ruminations:
Simulations cannot reproduce CIV/HI, or CIII/CIV, or CIV distribution. (But Metal cooling needed).
Galactic winds: hot, low filling-factor enrichment avoiding filaments.
But observations: cool, (relatively) high f.f., in filaments.
The observations are consistent with metals “sprinkled” at z > 5 with and ~ 0.75 dex, [Si/C] ~ 0.75.
Yet there are strong indications (observed winds, increase in Z by z ~ 0) that enrichment occurs at z < 4!
Could it be a mix?
Late winds may be compatible with observations: hidden in a hot phase with small filling factor, later becoming group/clusters enrichment.
Observed metals came earlier, don’t evolve.
How could we tell?
OVI (in progress) may be helpful.
More simulations (with cooling) can place limits.
Other ideas? (Pairs, UV/X-ray lines, etc.)
In short: much progress but much to be done.
Summary and Ruminations:
The scorecard
Test
Inhomogeneous, -dep. Z X
No evolution in Z observed. X
Warm, photoionized gas X?
[Si/C] ~ 0.75 ? ? ?
No evolution, scatter in [Si/C] X?
Lots of metal in IGM ? X?
Real picture: a conundum. Early and late?
Some questions/considerations: Metals sprinked in non-feedback simulation
reproduce all current observations. But… Do the observed winds escape? If so, where do the metals go?
If not winds, how to we fix baryon fraction in galaxies?
How do we close the cluster -- forest gap?
Metal from late galaxies may be hidden in unobservably hot gas, with low filling factor (and avoiding the filaments?)
Metal and H absorption does not have to come from same gas.
Data allows some evolution, esp. using freedom in UVB.
Metals in the IGM
Keck HIRES, z = 3.62
Compare metal lines to HI lines
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(10h-1 Mpc)3 box, 2163 SPH particles
Springel & Hernquist simulations
Springel & Hernquist simulations
Springel & Hernquist simulations
Springel & Hernquist simulations
normalized
Springel & Hernquist simulations
