Mass Profiles of Galaxy ClustersDrew Newman

Newman et al. 2009, “The Distribution of Dark Matter Over Three Decades in Radius in the Lensing Cluster Abell 611,” astro-ph/0909.3527, accepted to ApJ

• Purpose: Observational measures of cluster mass distribution (dark and baryonic) to make precise comparison with simulations (both N-body and those including baryons)

• Need data over wide range of scales to break degeneracies inherent to individual probes– Weak lensing (~100 kpc – 3 Mpc scales)– Strong lensing (~30 kpc – 100 kpc)– Stellar dynamics (~3 – 20 kpc)

Mass Model Motivation

• Focus on inner (log) density slope of dark matter

• Component #1: NFW / gNFW dark halo

• Component #2: Stars in the central galaxy

€

ρ(r) = ρ s(r /rs)

β (1+ r /rs)3−β

Weak Lensing – Abell 611Subaru/SuprimeCam

~10% ofarea shown

BVRI filtersfor photo-z’s

1 Mpc = 3.8’

Weak Lensing – Abell 611

Radial shear profile

2D mass reconstruction

Strong Lensing – Abell 611HST/ACS image

3 multiply images sources

2 of these with spectroscopic redshifts

Stellar VelocityDispersions – Abell 611

From Data to Mass Distributions• Draw sample models (MCMC) consisting of– Elliptical NFW or gNFW dark halo,– Stellar mass in cD galaxy,– Galaxies that may perturb image positions

• Compare to data:– Compute shear at locations of background galaxies,– Ray-tracing of multiply-imaged sources to other locations

in image plane,– Compute velocity dispersion profile (including

observational effects: seeing, binning)• Can we discriminate between NFW and gNFW DM

halos? If so, what is the inner slope allowed to be?

Results

• Definitely prefer a variable inner slope – Bayesian evidence larger

by factor (2.2 ± 1.0) x 104

• Logarithmic inner slope β < 0.3 (68%), i.e. quite shallow

Results

• Also, neither model reproduces the flat velocity dispersion profile

• How to match flat dispersion and lensing constraints at ~30-100 kpc?

DM-only simulations

• More modern cluster-scale simulations converge down to about 15 kpc/h

• Hints that slope become progressively more shallow

• But only on very small scales

Navarro et al 2004

Attempts to Include Baryons

• Adiabatic contraction– Cooling baryons contract

and “pinch” DM halo, steepening the cusp

– e.g. Gnedin et al. 2004, Gustafsson et al. 2007, Abadi et al. 2009, Pedrosa et al. 2009, etc.

– Cosmological N-body+gas dynamical simulations, with radiative cooling and attempts to include feedback processes

• Dynamical friction– Infalling baryon clumps

“heat” DM cusp, flattening it

– e.g. El-Zant et al. 2001, Romano-Diaz et al. 2008, Nipoti et al. 2004

– Frequent simplifications:• Infalling subhalos as purely

baryonic• Sometimes as unstrippable

point masses• Need to maintain clumps

over sufficient timescales without fragmenting, forming stars

Future

• Find density profile that is more observationally acceptable– Not a lot of theoretical motivation because

baryonic physics is not well enough understood• Extend to sample of ~10 clusters– All data collected for about half– For the rest, lack only velocity dispersions