Gravitational lensing by a structure in a cosmological background

Abstract

We use an exact general relativistic model structure within an FRW cosmological background based on a LTB metric to study the gravitational lensing by a cosmological and dynamical structure. Using different density profiles for the model structure, the deviation angle and the time delay through the gravitational lensing has been studied by solving the geodesic equations. The results of these exact calculations have been compared to the thin lens approximation. We have shown that the result for the thin lens approximation based on a modified NFW density profile with a void before going over to the FRW background matches very well with the exact general relativistic calculations. However, the thin lens approximation based on a normal NFW profile does differ from the exact relativistic calculation. The difference is more the less compact the structure is. We have also looked at the impact of our calculation on the observational interpretation of arcs in the case of strong lensing and also the reduced shear in the case of weak lensing. No significant difference has been seen in the data available.PACS numbers: 98.80. Jk, 98.62.Js, 98.62.Ck , 95.35.+d

The effects of structure anisotropy on lensing observables in an exact general relativistic setting for precision cosmology

“…The deviation at large r in the convergence is due to a small systematic error in choosing the appropriate equivalent FLRW distance, which the convergence is more sensitive to at very small values (large r). These results lend confidence to the method, however, in agreement with previous work with the LT metric which indicate good agreement between classical lensing results and those due to exact numerical calculations of the lensing properties of spherically symmetric structures [33,34]. Any systematic in the rescaling of the values due to the choice of FLRW distance will also not impact the results of this investigation, where we seek to examine the relative differences due to including anisotropy and are less interested in the absolute values of the convergence.…”

Studying the precision of ray tracing techniques with Szekeres models

“…Exact, inhomogeneous solutions to Einstein's field equations, such as the Szekeres models, are excellent tools for studying the validity and precision of results obtained by using mainstream approximation schemes. Such models have for instance been used to study the possibility of a giant void being the reason for the CMB cold spot [69][70][71], to study the precision of single structure thin lensing [55], and to illustrate the dominance of Doppler convergence at low redshifts [72].…”

Charged cosmological black hole

“…The main difference from an astrophysical black hole is that while ABH are static or asymptotically stationary, CBH have a dynamical horizon and a dynamical mass function. The lensing properties (the deviation angle and the time delay) of the CBH were shown to be different than the ABH thus making a testable prediction for this modeling of black hole [16] ; with the data available no significant difference was however reported.…”

“…And second many unknowns remains regarding collapsing structures and the process of formation of a black hole. Constructing such cosmological collapsing structures is not only useful to explore non-linear effect of GR but also to explore quasi-local features of that structure such as masses and horizons [5], black hole thermodynamics and Hawking radiation [6][7][8][9] or the validity of the weak field approximation [10].…”