DLAs in Cosmological SPH Simulations:

DLAs in Cosmological SPH
Simulations:
the “metallicity problem”
Ken Nagamine (Harvard-CfA)
Nov 2003
Volker Springel (MPA)
Lars Hernquist (Harvard-CfA)
(astro-ph/0302187, 0305409)

Outline
Brief introduction
Cosmological simulations
DLA cross section & abundance
Physical properties: S * , S SFR , Z/Z
The “metallicity problem”
Conclusions & Issues

Damped Lyman-a Absorbers (DLAs)
Quasar absorption system:
NHI >210 20 cm -2
Good probe of galaxy
formation at high-z.
Unclear origin:
disk?
(Wolfe & Prochaska)
protogalactic gas
clumps?
(Haehnelt, Steinmetz, &
Rauch)
(Peroux et al.)

Cosmological SPH Simulations
Framework: Flat LCDM model
P-GADGET2: TreePM-SPH code (Springel et al. 2000)
-- cooling/heating, UV background
-- multiphase model for gas particles
-- star formation & feedback (SN, galactic wind)
-- metal distribution
Improved SPH formulation:
‘Entropy formulation’
Alleviates previous problems:
overcooling, smearing of density
discontinuity
(Springel & Hernquist 2002a,b)

Simulation Parameters

Springel & Hernquist (2002)

Run
Box
[Mpc/h]
Np
M gas
[M/h]
m DM
[M/h]
e
[kpc/h]
z end
wind
O3 10. 1443 3.7e6 2.4e7 2.8 2.75 none
P3 10. 1443 3.7e6 2.4e7 2.8 2.75 weak
Q3 10. 1443 3.7e6 2.4e7 2.8 2.75 strong
Q4 10. 2163 1.1e6 7.2e6 1.9 2.75 strong
Q5 10. 3243 3.3e5 2.1e6 1.2 2.75 strong
D5 33.8 3243 1.3e7 8.2e7 4.2 1.00 strong
G5 100. 3243 1.1e9 7.2e9 8.0 0.0 strong

Neutral Hydrogen Density

~400 kpc comv
NHI
~300 kpc
DLAs
Q5 z=3

NHI
DLAs
Q5

DLA Cross Section vs. Mhalo
Power-law fit
strong
Previous study:
Gardner et al. (2000)

Cumulative DLA Abundance
Gardner
: power-law fit
obs.
nST :
Sheth & Tormen
analytic mass fcn.

Evolution of DLA Abundance
Consistent w obs at z ³ 2.5
(Peroux et al. 2003)
Uncertain at z < 2 because
of insufficient res.

NHI
Mstar
MZ
DLAs
SFR
metallicity

N HI
DLA
M
*
SFR
Z/Z
M Z

The “metallicity problem”
* Simulated áZ/Zñ too high
(comparable to LBGs)
Existence of high NHI,
high Z/Z systems.
[Same problems found by Cen
et al.]
Selection effect?
Dust Extinction?
Incomplete feedback ?
obs

The link to the “missing metal problem”
(Pettini)
(Wolfe et al. 2003)
“Where are the metals?”

Conclusions & Issues
Hydrodynamic simulations continue to improve.
WHI(z) , dN/dz, S * , S SFR look ok @ z³3.
(w. improved SPH formulation, SF & SN feedback, & resolution)
But…., the “metallicity problem” (cf. “missing metal
problem”)
more sophisticated treatment needed.
Even stronger feedback? Unlikely.
Hide metals in hot phase? Possible.
Galaxies: faint-end, proximity effect / Ly-a forest
Use full resources. Revealing the disagreement w
obs helps improving the simulations.

Additional Slides

f(N) of each halo

Distribution Function f(N)
Gamma-distribution
fit

Stellar Mass Density vs. NHI
Positive correlation
btw S star and NHI.
Star-to-gas ratio:
~ 1 (z=4.5)
~ 3 (z=3)
~ 10 (z=1)
~ 20 (z=0)

Projected SFR density vs. NHI
Positive correlation
btw SFR & NHI
Kennicutt Law
Î SFR = (2:5æ0:7) â 10 à 4
(Î gas=1:25â 10 20 cm à 2 ) 1:4æ0:15
[M ì =yr=kpc 2 ]

SFR vs. Metallicity

Evolution of Mean DLA Metallicity

PDF of DLA interception rate

Host Galaxy Magnitude vs. NHI
Wide range of
NHI absorption
systems should be
associated with
LBGs.

Galaxy Metallicity
LBGs: ~1/3 Z/Z
(Pettini 1999)
Consistent result
seen in Eulerian sims.
(Nagamine 2002)
LBGs

Effect of Resolution
Q3 (2.78 kpc/h) Q4 (1.85 kpc/h) Q5 (1.23 kpc/h)

Effect of Resolution (II)
Q3 (2.78 kpc/h) Q4 (1.85 kpc/h) Q5 (1.23 kpc/h)

Effect of Wind
O3 (none) P3 (weak) Q3 (strong)

Effect of Wind (II)
O3 (none) P3 (weak) Q3 (strong)

~400 kpc comv
M metal
~300 kpc comv
metallicity

~400 kpc comv ~300 kpc comv
DLAs
Mstar

~400 kpc comv ~300 kpc comv
DLAs
S SF

~400 kpc comv
Mstar
~300 kpc comv
metallicity