Zooming into the Cosmic Horseshoe: new insights on the lens profile and the source shape

Abstract

The gravitational lens SDSS J1148+1930, also known as the Cosmic Horseshoe, is one of the biggest and of the most detailed Einstein rings ever observed. We use the forward reconstruction method implemented in the lens fitting code Lensed to investigate with great detail the properties of the lens and of the background source. We model the lens with different mass distributions, focusing in particular on the determination of the slope of the dark matter component. The inherent degeneracy between the lens slope and the source size can be broken when we can isolate separate components of each lensed image, as in this case. For an elliptical power law model, $\kappa (r)\sim r^{-t}$, the results favour a flatter-than-isothermal slope with a maximum-likelihood value t = 0.08. Instead, when we consider the contribution of the baryonic matter separately, the maximum-likelihood value of the slope of the dark matter component is t = 0.31 or t = 0.44, depending on the assumed Initial Mass Function. We discuss the origin of this result by analysing in detail how the images and the sources change when the slope t changes. We also demonstrate that these slope values at the Einstein radius are not inconsistent with recent forecast from the theory of structure formation in the LambdaCDM model.

13 pages, 9 figures, accepted for publication in MNRAS

References in corpus (9)

• A Bayesian approach to strong lensing modelling of galaxy clusters
• The Observed properties of Dark Matter on small spatial scales
• Baryon effects on the internal structure of LCDM halos in the EAGLE simulations
• The Sloan Lens ACS Survey. VI: Discovery and analysis of a double Einstein ring
• The Cosmic Horseshoe: Discovery of an Einstein Ring around a Giant Luminous Red Galaxy
• Small scatter and nearly-isothermal mass profiles to four half-light radii from two-dimensional stellar dynamics of early-type galaxies
• Models of the Cosmic Horseshoe Gravitational Lens
• Super-resolving distant galaxies with gravitational telescopes: Keck-LGSAO and Hubble imaging of the lens system SDSSJ0737+3216
• The evolution of late-type galaxies from CASSOWARY lensing systems

Cited by in corpus (2)

• Galaxy mass profiles from strong lensing I: The circular power-law model
• The dynamical structure of broken power-law and double power-law models for dark matter haloes