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Investigating dark matter halos of galaxies from the COMBO-17 survey

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)

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Investigating dark matter halos of galaxies from the COMBO-17 survey

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  1. 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)

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

  3. 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!

  4. here: Strong lensing (distortions visible by eye) but we use: Weak lensing (distortions only detectable statistically) Abell 1689 HST/ACS STScI-PRC2003-01a

  5. Galaxy-galaxy lensing Images of background galaxies become tangentially aligned with respect to the lens lens model = SIS shear γ (“change in ellipticity”) ~ 0.035 but intrinsic ellipticities of galaxies ~ 0.35! => Distortion only measurable when averaging over thousands of lens galaxies no lens with lens

  6. 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)

  7. Data: COMBO-17 Deep – very good PSF - accurate phot-z • WFI@2.2m-telescope 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

  8. COMBO-17 filters

  9. SIS + Tully-Fisher Lens model: Lenses: R=18-24, zl=0.2-0.7 Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<150 h^-1 kpc Best-fit parameters and 1-σ errors:

  10. 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

  11. NFW: virial radius and concentration virial radius = radius inside which mean density is 200 times the mean density of the Universe Lens model: Lenses: R=18-24, zl=0.2-0.7 Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<400 h^-1 kpc

  12. NFW + “Tully-Fisher” Lens model: Lenses: R=18-24, zl=0.2-0.7 Sources: R=18-24, zl+0.1<zs<1.4 Pairs with r<400 h^-1 kpc Best-fit parameters and 1-σ errors:

  13. 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

  14. NFW: results virial radius = radius inside which mean density is 200 times the mean density of the Universe RCS, Hoekstra et al: M_vir=8.4±0.7x10^11h^-1M๏ (COMBO-17: 8.0+3.9-3.0 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: 9.8+4.4-3.4x10^11h^-1M๏, η=0.30+0.16-0.12)

  15. SIS+TF: Individual fields A901 S11 CDFS Difference of to result from all fields (156 km/s): A901 - 1σ, 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

  16. Summary Detection of galaxy-galaxy lensing signal in 3 fields: • SIS: σ*=156±18km/s, ηSIS=0.28+0.12-0.09 • NFW: rvir=217+24-32h^-1kpc, ηNFW=0.30+0.16-0.12 Mvir=7.1+2.6-2.7x10^11h^-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?

  17. A901: contribution from foreground clusters shear γ (κ~0) reduced shear γ/(1-κ) 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

  18. A901: contribution from foreground clusters and CBI shear γ (κ~0) reduced shear γ/(1-κ) 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

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

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