Galaxy-Galaxy lensing

1. Galaxy-Galaxy lensing Alexie Leauthaud Jean-Paul Kneib, Olivier Le Fevre, Lidia Tasca LAM (Laboratoire d’Astrophysique de Marseille) Jason Rhodes (JPL), Richard Massey (Caltech)

2. Galaxy-Galaxy Lensing 200 kpc Tangential ellipticity is proportional to tangential shear, γt γt = εt Shear is a measure of the total mass (dark and luminous) γt (r) ~ Σ(<r) - Σ(r)

3. …is a weak lensing technique • Weak shear cannot be detected from a single background source due to shape noise Galaxies are intrinsically elliptical with • < e > ~ 0.2 • < e2 > ~ 0.32 • Lensing induces shape correlations that can be measured by averaging over many lenses (~ 1000 ) • < γt > = < εt > • γ ~ 0.007 • Sensitivity: 0.3 / (N)1/2 Nice!…but rare

4. Probing Dark Matter Halos Dynamical methods work well within optical radius r < 20 kpc Satellite dynamics works at larger scales - System may not be in equilibrium - Interlopers make interpretation difficult Galaxy-Galaxy lensing is a unique method to probe galaxy Dark Matter Haloes ( DMH ) out to large radii 100h-1 kpc ~ 200 h-1 kpc

5. Aims : Galaxy mass function • Measure Galaxy Bias: how does total mass relate to luminous mass? • Understand how DMH vary with- Morphological type- Environment- Redshift • Constrain low mass end of Mass Function- critical ingredient for galaxy formation- predictions by N-body simulations- analytical predictionsFew observational constraints. Jenkins et al. 2000

6. Key to Galaxy Mass function • Galaxy-galaxy lensing requires that Lenses must be stacked. • Therefore, we probe DMH’s of a certain population. • Previous results limited by area and depth of surveys. Cosmos will allow fine binning so that specific populations can be studied. • If we assume stellar mass traces dark matter, then we can bin galaxies according to their stellar mass. In Progress: Galaxy-Galaxy lensing analysis of H-band selected Nicmos catalog prepared by Lidia Tasca ~ 6000 galaxies

7. Current state of work • Compiled ACS cycle 12/13 catalogSuggestions on this catalog are welcome! http://cencosw.oamp.fr/EN/index.en.html • Area : 1.2 sqr degre Number of objects : 400 000 Source density : ~ 60 sqr armin Lens density : ~ 10 sqr arcmin • Correlated with PhotoZ catalog: 68% correlation • Shapes of galaxies are measured with RRG method(Rhodes, Refregier and Groth, 2000) • PSF correction is performed using Tiny Tim models

8. Preliminary results Sheldon et al. astro-ph/0312036

9. 200 kpc Single lens approximation • Direct method • Can we assume a Clean LOS ? • Probability that a source will undergo multiple weak deflections must increase with the depth of the data set. • Multiple weak deflections lead to: • - Larger net and tangential shear • Overestimation of halo mass • Use Mockcatalogs with randomized ellipticities and simulate lensing (lenstool) to quatify error on mass. • NEXT STEP: Inverse methods Teresa Brainerd et al. astro-ph/0312036

10. Galaxy-galaxy flexion Flexion is a third order lensing term Combining shear + flexion leads to improved measures of galaxy masses Bacon et al. astro-ph/0504478 Flexion can be measured using the Shapelets formalism

11. Anisotropic lensing Evidence for non sphericql halos (X-ray isophotes, strong lensing) Stack lenses according to optical axis () - Dissipationless CDM models predict flattened halos  ~ 0.3 - Alternative models of gravity predict isotropic signal or