We present a multi-wavelength study of the gravitational lens COSMOS J095930+023427 (z=0.89), together with the associated galaxy group located at $zsim0.7$ along the line of sight and the lensed background galaxy. The source redshift is currently
unknown, but estimated to be at $z_s sim 2$. The analysis is based on the available public HST, Subaru, Chandra imaging data, and VLT spectroscopy. The lensing system is an early-type galaxy showing a strong [OII] emission line, and produces 4 bright images of the distant background source. It has an Einstein radius of 0.79, about 4 times large than the effective radius. We perform a lensing analysis using both a Singular Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution (PIEMD) for the lensing galaxy, and find that the final results on the total mass, the dark matter (DM) fraction within the Einstein radius and the external shear due to a foreground galaxy group are robust with respect of the choice of the parametric model and the source redshift (yet unknown). We measure the luminous mass from the photometric data, and find the DM fraction within the Einstein radius $f_{rm DM}$ to be between $0.71pm 0.13$ and $0.79 pm 0.15$, depending on the unknown source redshift. Meanwhile, the non-null external shear found in our lensing models supports the presence and structure of a galaxy group at $zsim0.7$, and an independent measurement of the 0.5-2 keV X-ray luminosity within 20 around the X-ray centroid provides a group mass of $M=(3-10)times 10^{13}$ M$_{odot}$, in good agreement with the previous estimate derived through weak lensing analysis.
We analyze a new gravitational lens, OAC-GL J1223-1239, serendipitously found in a deep I-band image of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). The lens is a L_*, edge-on S0 galaxy at z=0.4656. The gravitational arc has a
radius of 0.42 arcsec. We have determined the total mass and the dark matter (DM) fraction within the Einstein radius as a function of the lensed source redshift, which is presently unknown. For z ~ 1.3, which is in the middle of the redshift range plausible for the source according to some external constraints, we find the central velocity dispersion to be ~180 km/s. With this value, close to that obtained by means of the Faber-Jackson relation at the lens redshift, we compute a 30% DM fraction within the Einstein radius (given the uncertainty in the source redshift, the allowed range for the DM fraction is 25-35 % in our lensing model). When compared with the galaxies in the local Universe, the lensing galaxy, OAC-GL J1223-1239 seems to fall in the transition regime between massive DM dominated galaxies and lower-mass, DM deficient systems.
