* Astronomy

Title: What is the largest Einstein radius in the universe?
Authors: Masamune Oguri, Roger D. Blandford (KIPAC, Stanford)

The Einstein radius plays a central role in lens studies as it characterises the strength of gravitational lensing. The distribution of Einstein radii near the upper cutoff should probe the largest mass concentrations in the universe. Adopting a triaxial halo model, we compute expected distributions of large Einstein radii. To assess the cosmic variance, we generate a number of all-sky Monte-Carlo realisations. We find that the expected largest Einstein radius in the universe is sensitive to the cosmological model: for a source redshift z=1, they are 42^{+9}_{-7}, 35^{+8}_{-6}, and 54^{+12}_{-7} arcseconds, assuming best-fit parameters of the WMAP5, WMAP3 and WMAP1 data, respectively. These values are broadly consistent with current observations given their incompleteness. For the same source redshift, we expect in all-sky 35 (WMAP5), 15 (WMAP3), and 150 (WMAP1) clusters that have Einstein radii larger than 20''. Whilst the values of the largest Einstein radii are almost unaffected by the primordial non-Gaussianity currently of interest, the abundance of large lens clusters should probe non-Gaussianity competitively with CMB, but only if other cosmological parameters are well-measured. We also find that these "superlens" clusters constitute a highly biased population. For instance, a substantial fraction of these superlens clusters have major axes preferentially aligned with the line-of-sight. As a consequence, the projected mass distributions of the clusters are rounder by an ellipticity of 0.2 and have 40%-60% larger concentrations compared with typical clusters with similar redshifts and masses. We argue that the large concentration measured in A1689 is consistent with our model prediction at the 1.2\sigma level.

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Title: A Molecular Einstein Ring at z=4.12: Imaging the Dynamics of a Quasar Host Galaxy Through a Cosmic Lens
Authors: Dominik A. Riechers (1,2,7), Fabian Walter (1), Brendon J. Brewer (3), Christopher L. Carilli (4), Geraint F. Lewis (3), Frank Bertoldi (5), Pierre Cox (6) ((1) MPIA, Germany; (2) Caltech, USA; (3) Univ. of Sydney, Australia; (4) NRAO, USA; (5) AIfA Bonn, Germany; (6) IRAM, France; (7) Hubble Fellow)

We present high-resolution (0.3") Very Large Array (VLA) imaging of the molecular gas in the host galaxy of the high redshift quasar PSS J2322+1944 (z=4.12). These observations confirm that the molecular gas (CO) in the host galaxy of this quasar is lensed into a full Einstein ring, and reveal the internal dynamics of the molecular gas in this system. The ring has a diameter of ~1.5", and thus is sampled over ~20 resolution elements by our observations. Through a model-based lens inversion, we recover the velocity gradient of the molecular reservoir in the quasar host galaxy of PSS J2322+1944. The Einstein ring lens configuration enables us to zoom in on the emission and to resolve scales down to ~1 kpc. From the model-reconstructed source, we find that the molecular gas is distributed on a scale of 5 kpc, and has a total mass of M(H2)=1.7 x 10^10 M_sun. A basic estimate of the dynamical mass gives M_dyn = 4.4 x 10^10 (sin i)^-2 M_sun, that is, only ~2.5 times the molecular gas mass, and ~30 times the black hole mass (assuming that the dynamical structure is highly inclined). The lens configuration also allows us to tie the optical emission to the molecular gas emission, which suggests that the active galactic nucleus (AGN) does reside within, but not close to the centre of the molecular reservoir. Together with the (at least partially) disturbed structure of the CO, this suggests that the system is interacting. Such an interaction, possibly caused by a major `wet' merger, may be responsible for both feeding the quasar and fuelling the massive starburst of 680 M_sun/yr in this system, in agreement with recently suggested scenarios of quasar activity and galaxy assembly in the early universe.

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Astronomers using NASA's Hubble Space Telescope have compiled a large catalogue of gravitational lenses in the distant universe. The catalogue contains 67 new gravitationally lensed galaxy images found around massive elliptical and lenticular-shaped galaxies. This sample demonstrates the rich diversity of strong gravitational lenses. If this sample is representative, there would be nearly half a million similar gravitational lenses over the whole sky.
The COSMOS project, led by Nick Scoville at the California Institute of Technology, used observations from several observatories including Hubble, the Spitzer Space Telescope, the XMM-Newton spacecraft, the Chandra X-ray Observatory, the Very Large Telescope, and the Subaru Telescope.

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Title: The Sloan Lens ACS Survey. VI: Discovery and analysis of a double Einstein ring
Authors: Raphael Gavazzi (UCSB), Tommaso Treu (UCSB), Leon V.E. Koopmans (Kapteyn Astronomical Institute), Adam S. Bolton (IfA, CFA), Leonidas A. Moustakas (JPL), Scott Burles (MIT), Philip J. Marshall (UCSB)

We report the discovery of two concentric Einstein rings around the gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The main lens is at redshift zl=0.222, while the inner ring (1) is at zs1=0.609 and Einstein radius Re_1=1.43 ±0.01". The wider image separation (Re_2=2.07 ± 0.02") of the outer ring (2) implies that it is at higher redshift. Its detection in the F814W filter implies zs2<6.9. The configuration can be well described by a total density profile
ho_{tot} ~ r^-g' with g'=2.00 ±0.03 and velocity dispersion \sigma_{SIE}=287 ±5\kms. [...] We consider whether this configuration can be used to constrain cosmological parameters exploiting angular distance ratios entering the lens equations. Constraints for SDSSJ0946+1006, are uninteresting due to the sub-optimal lens and source redshifts. We then consider the perturbing effect of the mass associated with Ring 1 building a double lens plane compound lens model. This introduces minor changes to the mass of the main lens and allows to estimate the mass of Ring 1 (\sigma_{SIE,s1}=94 ±30\kms). We examine the prospects of doing cosmography with a sample of 50 double lenses, expected from future space based surveys such as DUNE or JDEM. Taking full account of the model uncertainties, such a sample could be used to measure Omega_m and w with 10% accuracy, for a flat cosmology.

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