Investigating dark matter halos of galaxies from the COMBO-17 survey Martina Kleinheinrich (Max-Planck-Institut für Astronomie, Heidelberg) & Hans-Walter Rix, Klaus Meisenheimer (Max-Planck-Institut für Astronomie, Heidelberg) Peter Schneider, Thomas Erben (Universität Bonn) Christian Wolf (University of Oxford) Mischa Schirmer (Isaac Newton Group of Telescopes, La Palma)

Outline of talk Scientific questions, motivation Introduction to galaxy-galaxy lensing Data set: COMBO-17 Measurements and results

Scientific questions Galaxies are embedded in large dark matter halos (evidence e.g. from rotation curves, dynamics of satellite galaxies, gravitational lensing, predicted by hierarchical clustering) What is the density profile of the dark matter halos? Mass? Extent? How does the density profile depend on galaxy properties, e.g. colour, type, luminosity, environment, stellar mass, redshift? Observational constraints needed for testing simulations of galaxy formation!

Abell 1689 HST/ACS STScI-PRC a here: Strong lensing (distortions visible by eye) but we use: Weak lensing (distortions only detectable statistically)

Galaxy-galaxy lensing Images of background galaxies become tangentially aligned with respect to the lens lens model = SIS shear γ (“change in ellipticity”) ~ but intrinsic ellipticities of galaxies ~ 0.35! => Distortion only measurable when averaging over thousands of lens galaxies no lens with lens

Outline of method Use distortions of background galaxies to measure halos of foreground galaxies Weak shear: only statistical analysis Identify lenses and sources (e.g. mag, z) Adopt lens model (e.g. SIS, NFW) Use maximum-likelihood technique to retrieve halo parameters (calculate shear from each lens at position of source and compare shape of source to predicted shear)

Data: COMBO-17 Deep – very good PSF - accurate phot-z on La Silla, 0.25 square degrees FOV 4 fields (3 used here) Limiting magnitude around R=25.5 R-band observations at seeing below 0.8” Spectral classification and redshifts from UBVRI and 12 medium-band filters, σ(z)<0.1, at R<21 σ(z)<0.01

COMBO-17 filters

SIS + Tully-Fisher Lens model: Lenses: R=18-24, zl= Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<150 h^-1 kpc Best-fit parameters and 1-σ errors:

SIS + TF: color dependence Color cut (red sequence): Bell et al. (2004) Blue galaxies (9898 lenses): Red galaxies (2579 lenses): 2-σ difference in velocity dispersion

NFW: virial radius and concentration Lens model: Lenses: R=18-24, zl= Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<400 h^-1 kpc virial radius = radius inside which mean density is 200 times the mean density of the Universe

NFW + “Tully-Fisher” Lens model: Lenses: R=18-24, zl= Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<400 h^-1 kpc Best-fit parameters and 1-σ errors:

NWF+TF: color dependence Color cut (red sequence): Bell et al. (2004) Blue galaxies (9169 lenses): Red galaxies (2415 lenses): 1-σ difference in virial radius and η

NFW: results r _vir h^- 1kpc ηM _vir 10^11h^ -1M๏ M/L h(M/L)๏ β M/L~L^β v _vir km/s v _max km/s c=20 r (vmax) h^-1kpc c=20 all blue red RCS, Hoekstra et al: M_vir=8.4±0.7x10^11h^-1M๏ (COMBO-17: x10^11h^-1M๏) SDSS, Guzik and Seljak (L*=1.51h^-2x10^10L๏): M_vir=8.96±1.59x10^11h^-1M๏, η=0.50±0.05 (COMBO-17: x10^11h^-1M๏, η= ) virial radius = radius inside which mean density is 200 times the mean density of the Universe

SIS+TF: Individual fields Difference of to result from all fields (156 km/s): A σ, S11 – 0σ, CDFS - 2σ Possible reasons: Foreground clusters in A901 and S11 Clusters at lens redshift PSF: 0.74”/ 0.88”/ 0.88” for A901/ S11/ CDFS Number counts: 4636/ 4268/ 3573 lenses in A901/ S11/ CDFS, 23.5%/ 20.5%/ 17.2% red lenses in A901/ S11/ CDFS A901S11 CDFS

Summary Detection of galaxy-galaxy lensing signal in 3 fields: SIS: σ*=156±18km/s, η SIS = NFW: r vir = h^-1kpc, η NFW = M vir = x10^11h^-1M๏ Differences between red and blue galaxies: SIS: velocity dispersion 40% larger (2-σ) for red galaxies NFW: virial mass >100% larger (1-σ) in red galaxies M/L increases with decreasing L in blue galaxies? M/L increases slightly with increasing L in red galaxies? Differences between 3 fields: Large differences between individual fields (up to 3-σ) Differences due to galaxy population/ number counts in fields?

A901: contribution from foreground clusters shear γ (κ~0)reduced shear γ/(1-κ) magnification μ Cluster model: three components, SIS (Taylor et al. 2004) σ(A901a)=680km/s, σ(A901b)=600km/s, σ(A902)=470km/s, z=0.16

A901: contribution from foreground clusters and CBI shear γ (κ~0)reduced shear γ/(1-κ) magnification μ Cluster model: four components, SIS (Taylor et al. 2004) σ(A901a)=680km/s, σ(A901b)=600km/s, σ(A902)=470km/s, z=0.16 σ(CBI)=730km/s, z=0.47

Individual fields: blue and red samples red blue A901 S11 CDFS