The Effect of Baryons and The Effect of Baryons and Dissipation on the Matter Dissipation on the Matter Power SpectrumPower Spectrum

Douglas Rudd (KICP, U. Chicago)Andrew Zentner & Andrey Kravtsov

astro-ph/0703741

Baryons vs Dark MatterBaryons vs Dark Matter

Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

Dynamics of baryons

different than dark matter

(shocks, pressure,

dissipation)

1E 0657-56, Bullet cluster

Gravity dominates at large scales and baryons trace dark

matter

At some scale this will change

Growth of Structure with Growth of Structure with BaryonsBaryons

Dark Matter only

Non-radiative Gas & DM

Cooling and Starformation

3 simulations with the same initial conditions

60 h-1 Mpc box, 2563 particles, 1 billion cells

Effect on Matter Power Effect on Matter Power SpectrumSpectrum

Simulation with cooling

Simulation without cooling

Scale dominated by large clusters

Huterer & Takada 2005

must theoretically predict nonlinear power spectrum P(k) to ~2% at k~1 h/Mpc to measure (σ8, Ωm, w)

See next talk by Charles Shapiro!

Weak lensing 2-d power spectrum relative to simulation without baryons

Effect of Cooling on Halo Effect of Cooling on Halo ProfilesProfiles

“Adiabatic Contraction”

Blumenthal et al (1986), Gnedin et al (2004)

Cumulative mass profile

for most massive cluster

Mass distribution

altered beyond virial radius

Limited resolution leads to

“overcooling”

Cooling of baryons

Dark Matter Halo Dark Matter Halo ConcentrationsConcentrations

NFW fits to DM halo density profiles excluding inner 0.05 Rvir

~40% increase in cooling simulation

cvir = Rvir / rs

Halo Mass

~10% increase in non-radiative simulation

See also

Lin et al 2006 Rasia et al 2004

Effect on parameter Effect on parameter estimationestimation

Now normalize

d to simulation

with cooling,

aka “reality”

2

DMDM

CSFCSFDM ),/(

),/()()(P

ccRk

ccRkkPk

Simple Model

•λ – “one-halo” contribution to power spectrum (Fourier-transform of NFW profile)

•R – size of typical halo ~Mpc

•cDM,cCSF – concentration of typical halo in DM simulation vs simulation with cooling

ConclusionsConclusions

Baryons change structure of dark halos even when baryons can’t cool (not just adiabatic contraction!)

Can model the effect of baryons as a shift in concentration relative to dissipationless simulations

Current simulations unable to predict absolute magnitude of effect, but non-radiative simulation demonstrates robust lower limit

Next step: see how adding additional parameters affects cosmological parameter constraints

astro-ph/0703741