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Register a new userModel-independent and model-based local lensing properties of CL0024+1654 from multiply-imaged galaxies
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We investigate to which precision local magnification ratios, $mathcal{J}$, ratios of convergences, $f$, and reduced shears, $g = (g_{1}, g_{2})$, can be determined model-independently for the five resolved multiple images of the source at $z_mathrm{s}=1.675$ in CL0024. We also determine if a comparison to the respective results obtained by the parametric modelling program Lenstool and by the non-parametric modelling program Grale can detect biases in the lens models. For these model-based approaches we additionally analyse the influence of the number and location of the constraints from multiple images on the local lens properties determined at the positions of the five multiple images of the source at $z_mathrm{s}=1.675$. All approaches show high agreement on the local values of $mathcal{J}$, $f$, and $g$. We find that Lenstool obtains the tightest confidence bounds even for convergences around one using constraints from six multiple image systems, while the best Grale model is generated only using constraints from all multiple images with resolved brightness features and adding limited small-scale mass corrections. Yet, confidence bounds as large as the values themselves can occur for convergences close to one in all approaches. Our results are in agreement with previous findings, supporting the light-traces-mass assumption and the merger hypothesis for CL0024. Comparing the three different approaches allows to detect modelling biases. Given that the lens properties remain approximately constant over the extension of the image areas covered by the resolvable brightness features, the model-independent approach determines the local lens properties to a comparable precision but within less than a second. (shortened)
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The galaxy-scale gravitational lens B0128+437 generates a quadrupole-image configuration of a background quasar that shows milli-arcsecond-scale subcomponents in the multiple images observed with VLBI. As this multiple-image configuration including the subcomponents has eluded a parametric lens-model characterisation so far, we determine local lens properties at the positions of the multiple images with our model-independent approach. Using PixeLens, we also succeed in setting up a global free-form mass density reconstruction including all subcomponents as constraints. We compare the model-independent local lens properties with those obtained by PixeLens and those obtained by the parametric modelling algorithm Lensmodel. A comparison of all three approaches and a model-free analysis based on the relative polar angles of the multiple images corroborate the hypothesis that elliptically symmetric models are too simplistic to characterise the asymmetric mass density distribution of this lenticular or late-type galaxy. In addition, the model-independent approach efficiently determines local lens properties on the scale of the quasar subcomponents, which are computationally intensive to obtain by free-form model-based approaches. As only 40% of the small-scale subcomponent local lens properties overlap within the 1-$sigma$ confidence bounds, mass density gradients on milli-arcsecond scales cannot be excluded. Hence, aiming at a global reconstruction of the deflecting mass density distribution, increasingly detailed observations require flexible free-form models that allow for density fluctuations on milli-arcsecond scale to replace parametric ones, especially for asymmetric lenses or lenses with localised inhomogeneities like B0128.
We derive an accurate mass distribution of the rich galaxy cluster Cl0024+1654 (z=0.395) based on deep Subaru BR_{c}z imaging and our recent comprehensive strong lensing analysis of HST/ACS/NIC3 observations. We obtain the weak lensing distortion and magnification of undilted samples of red and blue background galaxies by carefully combining all color and positional information. Unlike previous work, the weak and strong lensing are in excellent agreement where the data overlap. The joint mass profile continuously steepens out to the virial radius with only a minor contribution sim 10% in the mass from known subcluster at a projected distance of sim 700kpc/h. The projected mass distribution for the entire cluster is well fitted with a single Navarro-Frenk-White model with a virial mass, M_{vir} = (1.2 pm 0.2) times 10^{15} M_{sun}/h, and a concentration, c_{vir} = 9.2^{+1.4}_{-1.2}. This model fit is fully consistent with the depletion of the red background counts, providing independent confirmation. Careful examination and interpretation of X-ray and dynamical data strongly suggest that this cluster system is in a post collision state, which we show is consistent with our well-defined mass profile for a major merger occurring along the line of sight, viewed approximately 2-3Gyr after impact when the gravitational potential has had time to relax in the center, before the gas has recovered and before the outskirts are fully virialized. Finally, our full lensing analysis provides a model-independent constraint of M_{2D}(<r_{vir}) = (1.4 pm 0.3) times 10^{15} M_{sun}/h for the projected mass of the whole system, including any currently unbound material beyond the virial radius, which can constrain the sum of the two pre-merger cluster masses when designing simulations to explore this system.
We analyse the surface density of very faint galaxies at the limit of the sky background noise in the field of the cluster of galaxies Cl0024+1654. The radial variation of their number density in the magnitude bins $B=26-28$ and $I=24-26.5$ displays an (anti)bias magnification effect for $I < 24$ which provides the redshift range of the populations seen in $B$ and $I$. The depletion curve can be reproduced with two redshift populations with $60% pm 10%$ of the $B$ galaxies between $z=0.9$ and $z=1.1$ and the remaining at a redshift close to $z=3$. The $I$ selected population is similar but with a minimum extending from the $B$ inner critical line to $R_I=60$. Whatever the cosmological model, the $I$-selected galaxies spread up to a larger redshift with about 20% above $z > 4$. Using a model for the gravitational potential, the locations of the two extreme critical lines for the B and I galaxies favour $Omega_{Lambda}$-dominated flat universes with a cosmological constant ranging from 0.6 to 0.9. The result is confirmed by a preliminary investigation of A370. We discuss the method to search the last critical line and the various biases.
When light from a distant source object, like a galaxy or a supernova, travels towards us, it is deflected by massive objects that lie on its path. When the mass density of the deflecting object exceeds a certain threshold, multiple, highly distorted images of the source are observed. This strong gravitational lensing effect has so far been treated as a model-fitting problem. Using the observed multiple images as constraints yields a self-consistent model of the deflecting mass density and the source object. As several models meet the constraints equally well, we develop a lens characterisation that separates data-based information from model assumptions. The observed multiple images allow us to determine local properties of the deflecting mass distribution on any mass scale from one simple set of equations. Their solution is unique and free of model-dependent degeneracies. The reconstruction of source objects can be performed completely model-independently, enabling us to study galaxy evolution without a lens-model bias. Our approach reduces the lens and source description to its data-based evidence that all models agree upon, simplifies an automated treatment of large datasets, and allows for an extrapolation to a global description resembling model-based descriptions.
Applying the distance sum rule in strong gravitational lensing (SGL) and type Ia supernova (SN Ia) observations, one can provide an interesting cosmological model-independent method to determine the cosmic curvature parameter $Omega_k$. In this paper, with the newly compiled data sets including 161 galactic-scale SGL systems and 1048 SN Ia data, we place constraints on $Omega_k$ within the framework of three types of lens models extensively used in SGL studies. Moreover, to investigate the effect of different mass lens samples on the results, we divide the SGL sample into three sub-samples based on the center velocity dispersion of intervening galaxies. In the singular isothermal sphere (SIS) and extended power-law lens models, a flat universe is supported with the uncertainty about 0.2, while a closed universe is preferred in the power-law lens model. We find that the choice of lens models and the classification of SGL data actually can influence the constraints on $Omega_k$ significantly.
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