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)

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)

…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

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

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 predictions Few observational constraints. Jenkins et al. 2000

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

Current state of work Compiled ACS cycle 12/13 catalog Suggestions 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

Preliminary results Sheldon et al. astro-ph/0312036

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 200 kpc Teresa Brainerd et al. astro-ph/0312036

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

Anisotropic lensing or 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