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Lens Galaxy (lens + galaxy)
Selected AbstractsGalaxy,galaxy lensing by non-spherical haloes , I. Theoretical considerationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010Paul J. Howell ABSTRACT We use a series of Monte Carlo simulations to investigate the theory of galaxy,galaxy lensing by non-spherical dark matter haloes. The simulations include a careful accounting of the effects of multiple deflections on the galaxy,galaxy lensing signal. In a typical observational data set where the mean tangential shear of sources with redshifts zs, 0.6 is measured with respect to the observed symmetry axes of foreground galaxies with redshifts zl, 0.3, we find that the signature of anisotropic galaxy,galaxy lensing differs substantially from the simple expectation that one would have in the absence of multiple deflections. In general, the observed ratio of the mean tangential shears, ,+(,)/,,(,), is strongly suppressed compared to the function that one would measure if the intrinsic symmetry axes of the foreground galaxies were known. Depending upon the characteristic masses of the lenses, the observed ratio of the mean tangential shears may be consistent with an isotropic signal (despite the fact that the lenses are non-spherical), or it may even be reversed from the expected signal (i.e. the mean tangential shear for sources close to the observed minor axes of the lenses may exceed the mean tangential shear for sources close to the observed major axes of the lenses). These effects are caused primarily by the fact that the images of the lens galaxies have, themselves, been lensed and therefore the observed symmetry axes of the lens galaxies differ from their intrinsic symmetry axes. We show that the effects of lensing of the foreground galaxies on the observed function ,+(,)/,,(,) cannot be eliminated simply by the rejection of foreground galaxies with very small image ellipticities nor by simply focusing the analysis on sources that are located very close to the observed symmetry axes of the foreground galaxies. We conclude that any attempt to use a measurement of ,+(,)/,,(,) to constrain the shapes of dark matter galaxy haloes must include Monte Carlo simulations that take multiple deflections properly into account. [source] A search for the third lensed image in JVAS B1030+074MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. Zhang ABSTRACT Central gravitational image detection is very important for the study of the mass distribution of the inner parts (,100 pc) of lens galaxies. However, the detection of such images is extremely rare and difficult. We present a 1.7-GHz High Sensitivity Array (HSA) observation of the double-image radio lens system B1030+074. The data are combined with archive Very Long Baseline Array and global very long baseline interferometry (VLBI) observations, and careful consideration is given to the effects of noise, cleaning and self-calibration. An upper limit is derived for the strength of the central image of 180 ,Jy (90 per cent confidence level), considerably greater than would have been expected on the basis of a simple analysis. This gives a lower limit of ,103 for the ratio of the brightest image to the central image. For cusped models of lens mass distributions, we have made use of this non-detection to constrain the relation between inner power-law slope , of the lensing galaxy mass profile, and its break radius rb. For rb > 130 pc the power-law slope is required to be close to isothermal (, > 1.8). A flatter inner slope is allowed if a massive black hole is present at the centre of the lensing galaxy, but the effect of the black hole is small unless it is ,10 times more massive than that implied by the relation between black hole mass and stellar velocity dispersion. By comparing four epochs of VLBI observations, we also detected possible superluminal motion in the jet in the brighter image A. The B jet remains unresolved, as expected from a simple lens model of the system. [source] Models of the Cosmic Horseshoe gravitational lens J1004+4112MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008S. Dye ABSTRACT We model the extremely massive and luminous lens galaxy in the Cosmic Horseshoe Einstein ring system J1004+4112, recently discovered in the Sloan Digital Sky Survey. We use the semilinear method of Warren & Dye, which pixelizes the source surface brightness distribution, to invert the Einstein ring for sets of parametrized lens models. Here, the method is refined by exploiting Bayesian inference to optimise adaptive pixelization of the source plane and to choose between three differently parametrized models: a singular isothermal ellipsoid, a power-law model and a Navarro, Frenk & White (NFW) profile. The most probable lens model is the power law with a volume mass density ,,r,1.96±0.02 and an axis ratio of ,0.8. The mass within the Einstein ring (i.e. within a cylinder with projected distance of ,30 kpc from the centre of the lens galaxy) is (5.02 ± 0.09) × 1012 M ,, and the mass-to-light ratio is ,30. Even though the lens lies in a group of galaxies, the preferred value of the external shear is almost zero. This makes the Cosmic Horseshoe unique amongst large separation lenses, as almost all the deflection comes from a single, very massive galaxy with little boost from the environment. [source] The internal structure of the lens PG1115+080: breaking degeneracies in the value of the Hubble constantMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002T. Treu ABSTRACT We combine lensing, stellar kinematic and mass-to-light ratio constraints to build a two-component (luminous plus dark) mass model of the early-type lens galaxy in PG1115+080. We find a total mass density profile steeper than r,2, effectively ,,r,,, with ,,= 2.35 ± 0.1 ± 0.05 (random + systematic). The stellar mass fraction is f*= 0.67+0.20,0.25± 0.03 inside the Einstein radius (RE, 1.2 effective radii). The dynamical mass model breaks the degeneracies in the mass profile of the lens galaxy and allows us to obtain a value of the Hubble constant that is no longer dominated by systematic errors: H0= 59+12,7± 3 km s,1 Mpc,1 (68 per cent confidence level; ,m= 0.3, ,,= 0.7). The offset of PG1115+080 from the Fundamental Plane might indicate deviations from homology of the mass profile of some early-type galaxies. [source] The dark halo of the main lens galaxy in QSO 0957 + 561MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005L. J. Goicoechea ABSTRACT We present an analysis of infrared/optical/ultraviolet spectra of the two images of the first gravitationally lensed quasar Q0957 + 561A,B. The Hubble Space Telescope observations of Q0957 + 561A and Q0957 + 561B are separated in time by the known time delay in this system, so we can directly deduce the flux ratios. These flux ratios of images lead to important information on the dark halo of the main lens galaxy (a giant elliptical at redshift z= 0.36). Our measurements for the continuum are in good agreement with extinction in the elliptical galaxy and a small fraction of mass in collapsed objects (no need for gravitational microlensing). From the continuum and emission-line ratios, we also show evidence in favour of the existence of a network of compact dusty clouds. [source] | ||||||||||