Probing dark matter halos atredshifts z=[1,3] with lensing magnification

L. Van Waerbeke

With H. Hildebrandt (Leiden) J. Ford (UBC) M. Milkeraitis (UBC)

CIfAR Lake LouiseFeb 18-21 2010

Why are high redshift DM halos interesting?

-N(M,z) is a strong probe of cosmology/DE (cf Gill’s talk)

-DM halo shape/profile can provide a test of CDM

-make an observational connection between galaxy/cluster formationand DM environment

Lensing studies are exclusively interested in shear )

Limitations/difficulties with the shear:

-requires very accurate Point Spread Function correction to measure theShape of distant galaxies

-this limits how small source galaxies can be, i.e. how far they can be. In practice there is little hope to precise measurement above zsource ~1

-this limits the maximum redshift one can probe the dark matter distribution,i.e. zlens ~0.5-1.

What is cosmic magnification?

magnification depends on shear and convergence:

The number of lensed objects at magnitude m:

Where is the number count slope.

2D number density contrast at sky position :

d

Convergence profile of A1689 (Taylor et al 1998)Magnification profile in A1689 (Taylor et al 1998)

Two sources of noise:-Statistical (Poisson)-Clustering of bck sources

Advantages of magnification:

-does NOT requires Point Spread Function correction to measure the photometry.

-there is NO limits how small source galaxies can be, i.e. how far they can be.

-there is NO limits on the maximum redshift one can probe the dark matter distribution as long you can find enough sources behind.

Can we probe redshift z=[1,3] dark matter halos with optical data?

We looked at LBGs in CFHTLS deep data with the dropout technique(cf Ellis’s talk).

Redshift z=3 LBGSpectral energy distribution

LBG counts in CFHTLS Deep (4 sq.deg. Deep MEGACAM) is used tocalibrate the slope

Hildebrandt et al. 2009

ug dropout with z=[0.5,1] foregrounds

Hildebrandt et al 2009

Magnification correlation fct

DM halo magnification: proof of concept on 15 SpARCS high-z clusters (PI: Wilson)

Expected cumulative number density n(>z) of halos for a250 sq.deg. Survey, CFHTLS depth (i<24.5) (taken from MS, 8 adjusted):

(for

a 2

50 s

q.de

g. F

OV

)

1-5 1013 Mo

>3 1014 Mo

1-2 1014 Mo

Stacked signal forHalos at z>1

Full error fromCFHTLSW LBGs

Conclusions:

-new window on DM studies: magnification can probe darkmatter halos in a redsfhit range inaccessible byshear measurements.

-complementarity: combined with shear measurement forredshift z<1 clusters it can constrain intrinsic alignment.

-can be used to get the average mass from baryonicproxy (SZ, Xray, 21cm)

-much easier technically than shear: we already know itcan be done from ground based and balloon observatories.

Caveats:

-loss in SNR is ~5, but gain in sources number densityis ~2. Net SNR loss is ~2-3.

-dust absorption. Small effect but detectable at thepercent level (Menard 2009). Multiwavelength data canactually measure both!

-Eddington bias

-need to find targets (need a cluster proxy, not necessarilymass).Easy for low mass and high mass DM halos. Not easy forlow cluster mass/groups.