1. The Effect of Baryons and Dissipation on the Matter Power Spectrum Douglas Rudd (KICP, U. Chicago) Andrew Zentner & Andrey Kravtsov astro-ph/0703741

2. Baryons 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

3. Growth of Structure with Baryons Dark Matter only Non-radiative Gas & DMCooling and Starformation 3 simulations with the same initial conditions 60 h -1 Mpc box, 256 3 particles, 1 billion cells

4. Effect on Matter Power Spectrum 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 (σ 8, Ω m, w) See next talk by Charles Shapiro! Weak lensing 2-d power spectrum relative to simulation without baryons

5. Effect of Cooling on Halo Profiles “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

6. Dark Matter Halo Concentrations NFW fits to DM halo density profiles excluding inner 0.05 R vir ~40% increase in cooling simulation c vir = R vir / r s Halo Mass ~10% increase in non-radiative simulation See also Lin et al 2006 Rasia et al 2004

7. Effect on parameter estimation Now normalized to simulation with cooling, aka “reality” Simple Model λ – “one-halo” contribution to power spectrum (Fourier- transform of NFW profile) R – size of typical halo ~Mpc c DM,c CSF – concentration of typical halo in DM simulation vs simulation with cooling

8. Conclusions 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