Dark matter and strong

lensingTOMMASO TREU (UCSB)

Outline Introduction

Cosmography

Three key questions: Are dark matter halo profiles universal?

(warm/ interactive dark matter?) Universal halos or universal stellar

initial mass function? (a.k.a. non-baryonic dark matter?)

Is there dark matter substructure? (mass of the dark matter particle?)

Strong gravitational Lensing

Image separation is a direct measurement of mass, luminous or dark!

Why is it called Lensing?

Courtesy of P.J.Marshall

Strong lensing is rare (1/1000 galaxy) but we know how to find lots of them

Strong lensing in terms of Fermat’s principle

Excess time delay

Fermat distance

geometric time delay

Shapiro delay

Cosmography

H0 is needed for accurate measurements of

•Dark matter density•Flatness•Neutrino masses•Dark energy equation of state•…..

See Verde’s and Reid’s talk

Cosmography from time delays:

how does it work?

Cosmography with strong lenses:

4 solved problems Time delay – 2-3 %

Astrometry – 10-20 mas

Lens potential (2-3%)

Structure along the line of sight (2-3%)

Suyu et al. 2010

Constraints for w=-1

Suyu et al. 2010

Constraints on Dark Energy

For curved wCDM

With WMAP7:

• B1608+656 is comparable to BAO [Percival et al. 2010]

• B1608+656 and BAO both primarily constrain k

• SN [Hicken et al. 2009]

primarily constrains w

Future Prospects

•Precision is 6-7% per system on H0 • Currently ~10 lenses have precise time-delays•Precision on H0 of <3% is attainable now•Future telescopes (e.g. LSST) will discover and measure 100s of time delays (Oguri & Marshall 2010; Treu 2010)

Are dark matter profiles

universal? (warm/self

interacting dark

matter?)

The mass density profile of dark matter halos

•Is the dark matter profile universal and “cuspy” as suggested by simulations?•If not, it may be a sign that dark matter is warm or self- interacting

De Blok’s talk

Observational challenges…

•Precision over a large dynamic range in mass•Disentangle luminous and dark matter•Control systematics

… can be overcome in clusters by combining

methods•Stellar kinematics (<30 kpc)•Strong lensing (<100 kpc)•X-ray (0.05 – 0.5 Mpc)•Weak lensing (0.1-3 Mpc)

Sand, Treu, Ellis 2002; Sand et al. 2004,2008; Newman et al. 2009,2011

Newman et al 2011

Results for Abell 611

Newman et al. 2009

Results for Abell 383

Range of N-body resultsfor pure DM halo

Newman et al. 2011

More clusters on the way, see also Postman’s MCT

The role of baryons

Baryonic cooling and star formation tends to drive material towards the center and thus make the inner slope steeper than for DM only

In simulations, the amount of steepening depends on the cluster merger history and the details of baryonic physics, because dynamical friction can counterbalance - at least in part - the effect

Universal Halos or

Universal Stellar Initial

Mass function?

(Baryonic or non

baryonic?)

Massive ellipticals have “too much” dark matter?

Treu et al. 2010

Stellar mass from lensing and dynamics

Ste

llar

mass f

rom

fro

m

colo

rs

Universal halos or IMF?

Auger, TT et al. 2010

Salpeter

Kroupa

ChabrierIMF “

mis

matc

h”

Mass dependency

What about spirals?

Dutton et al. 2011; Treu et al. 2011

What about spirals?

Treu et al. 2011Dutton et al. 2011

Is there dark matter

substructure?

(Mass of the dark

matter particle)

Milky Way (missing) satellites

Kravtsov 2010 Strigari et al. 2007

Are they dark or do they not exist?

“Missing satellites” and strong lensing

• Strong lensing detects satellites based on mass

• Satellites are detected as “anomalies” in the gravitational potential ψ

– ψ’’ = magnification anomalies

– ψ’ = astrometric anomalies

– ψ = time delay anomalies

Moustakas’ talk

Gravitational mass imaging: idea

Mass substructure distorts extended lensed sources

Direct detection of a dark substructure

Vegetti et al 2010

Dark matter and strong lensing: Answers

Is there dark matter? What is it? Yes. We can help find out with time-delays

Are dark matter halo profiles universal? No. Either we do not understand baryons or

we do not understand dark matter

Is the IMF universal? No, If we understand dark matter halos.

Is there dark matter substructure? Yes. Not clear if there is enough (or maybe

too much)

The end