A twelve-image gravitational lens system in the z 0.84 cluster Cl J0152.7-1357*
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany e-mail: firstname.lastname@example.org
2 Università degli Studi di Milano, Department of Physics, via Celoria 16, 20133 Milan, Italy
3 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
4 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19011, Santiago 19, Chile
5 Universidad de Valparaíso, Departamento de Física y Astronomia, Avda. Gran Bretaña 1111, Valparaíso, Chile
6 INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34141 Trieste, Italy
Accepted: 6 May 2008
Context. Gravitational lens modeling is presented for the first discovered example of a three-component source for which each component is quadruply imaged. The lens is a massive galaxy member of the cluster Cl J0152.7-1357 at z 0.84.
Aims. Taking advantage of this exceptional configuration and of the excellent angular resolution of the HST Advanced Camera for Surveys (ACS), we measure the properties of the lens. In particular, the lensing mass estimates of the galaxy are compared to those from stellar dynamics and multiwavelength photometry.
Methods. Several parametric macroscopic models were developed for the lens galaxy, starting from pointlike to extended image models. By combining lensing, stellar dynamics, photometry, and spectroscopy, we find an allowed range of values for the redshift of the source and the required minimum amount of dark matter enclosed within the disk defined by the Einstein ring of the lens.
Results. For a lens model in terms of a singular isothermal sphere with external shear, the Einstein radius is found to be RE = 9.54 ± 0.15 kpc. The external shear points to the cluster's northern mass peak. The unknown redshift of the source is determined to be higher than 1.9 and lower than 2.9. Our estimate of the lensing projected total mass inside the Einstein radius, (R ≤ 9.54 kpc), depends on the source distance and lies between 4.6 and 6.2 1011 . This result turns out to be compatible with the dynamical estimate based on an isothermal model. By considering the constraint on the stellar mass-to-light ratio that comes from the evolution of the Fundamental Plane, we can exclude the possibility that at more than 4σ level the total mass enclosed inside the Einstein ring is only luminous matter. Moreover, the photometric-stellar mass measurement within the Einstein radius gives a minimum value of 50% (1σ) for the dark-to-total matter fraction.
Conclusions. The lensing analysis has allowed us to investigate the distribution of mass of the deflector, also providing some interesting indications on scales that are larger (cluster) and smaller (substructure) than the Einstein radius of the lens galaxy. The combination of different diagnostics has proved to be essential in determining quantities that otherwise would have not been directly measurable (with only the currently available data): the redshift of the source and the amount of dark matter in the lens.
Key words: cosmology: observations / galaxies: high-redshift / galaxies: elliptical and lenticular, cD / dark matter / gravitational lensing / galaxies: kinematics and dynamics
© ESO, 2008