Probing dark matter halos at redshifts z=[1,3] with lensing magnification
Dark matter and strong lensing
description
Transcript of Dark matter and strong lensing
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