Line-of-sight Shear In SLACS Strong Lenses
Context. Inhomogeneities alongside the line of sight in sturdy gravitational lensing distort the photographs produced, in an impact called shear. If measurable, this shear might present independent constraints on cosmological parameters, complementary to conventional cosmic shear. Aims. We mannequin 50 sturdy gravitational lenses from the Sloan Lens ACS (SLACS) catalogue with the aim of measuring the line-of-sight (LOS) shear for the primary time. We use the ‘minimal model’ for the LOS shear, which has been shown to be theoretically safe from degeneracies with lens model parameters, a discovering which has been confirmed utilizing mock data. Methods. We use the dolphin automated modelling pipeline, which uses the lenstronomy software as a modelling engine, to mannequin our chosen lenses. We model the main deflector with an elliptical Wood Ranger Power Shears shop legislation profile, the lens gentle with elliptical Sérsic profiles and the supply with a basis set of shapelets and an elliptical Sérsic profile. Results. We successfully acquire a line-of-sight shear measurement from 18 of the 50 lenses.
We discover that these LOS shear measurements are per exterior Wood Ranger Power Shears website measured in latest works using a easier shear model, that are bigger than those expected from weak lensing. Neglecting the post-Born correction to the potential of the principle deflector due to foreground shear leads to a propagation of degeneracies to the LOS shear measurement, and the same impact is seen if a prior is used to connect the lens mass and gentle ellipticities. The inclusion of an octupole second in the lens mass profile doesn't result in shear measurements which are in better agreement with the expectations from weak lensing. Gravitational lensing provides a unique window into the cosmology of our Universe on a wide range of scales. Refsdal, 1964; Wong et al., 2020; Birrer et al., 2020, 2024) through observations of the distinction in arrival times of photos of variable sources. The weak lensing regime probes bigger scales. Unlike robust lensing, a number of images of the same supply should not produced; rather, small distortions are induced on the single picture of every supply, artificially squashing and aligning them.
The main order shape distortion is shear, and its effect cannot be disentangled from the intrinsic form of particular person galaxies or their intrinsic alignment. The cosmic shear sign is detected by correlating the shapes of millions of galaxies in a given galaxy survey. By advantage of their existence in our inhomogeneous Universe, sturdy lensing images may also expertise weak lensing distortions, with Einstein rings particularly supplying the notion of a ‘standardisable shape’ from which shear may be robustly measured111In apply, shear may be recovered even when the picture shouldn't be a complete Einstein ring, although the precision of the measurement could also be degraded (Hogg et al., 2023)., providing an alternate and independent probe of cosmology to the standard weak lensing shear. This concept was first investigated by Birrer et al. 4133 with a shear model that consisted of four parameters: two elements to describe the foreground shear as projected onto the lens plane, and wood shears two parts to explain the background shear as projected onto the supply plane.
Whilst the shear parameters have been shown to be constrained with high precision, this analysis revealed sturdy degeneracies between the shear parameters and the elements of the ellipticity of the lens mass. This means that, with this mannequin, the constraints on the shear cannot be disentangled from the constraints on the lens mass, and the measurements cannot be safely used to acquire cosmological info. Fleury et al. (2021) developed the minimal line-of-sight shear mannequin to address this drawback. Starting with three separate wood shears, the model exploits a supply-position transformation to construct a shear parameter, the ‘line-of-sight (LOS) shear’, which at main order (i.e. for small values of the shear) is mathematically free from degeneracy with any parameter used to describe the lens mass. The model fully describes the problem with the fewest possible parameters, and is therefore known as the minimal LOS shear model - we are going to evaluate the formalism behind this model in more element beneath. Because of this freedom from degeneracies, it's the LOS shear within the minimal model which ought to be focused for eventual cosmological inference.
