Could the Gravitational Lensing Alter the Interpretations of the Observational Data in the Extragalactic Field?

Abstract

To deduce intrinsic source properties (absolute luminosity, radio flux, size…), we currently use z as a distance indicator; following the Friedmann (or R-W) model, the main relations are based on the Cosmological Principle. However, there are inhomogeneities of (luminous or dark) matter up to 100 Mpc which potentially modify light beams passing near or across them. This is describe by the gravitational optics theory. It leads to:

• →a change of the source location (/ of the null deflecting mass).

• →temporal effects (time-delay and redshift effects).

• → affect the light beam properties following the Optical Scalar Equations (Sachs, 1961). It depends on two main terms, both being proportional to the geometrical term D_dD_ds/D_s (angular diameter distances, d: deflector, s:source): (1) K (Ricci term) due to the matter contained into the beam, which provides an expansion of the beam without distorts it; (2) Γ (shear term) due to the matter contained into the beam, which distorts and may multiply the beam. Note that the source surface brightness is unchanged by the gravitational lensing, but its surface is amplified by Amp=[(1 —K)²—Γ²]⁻¹ It does not depend on the wavelength (geom. optic approxim.), but may apparently change the source color by either a differential lensing of a source for which the spatial structure depends on wavelength, or a blend of the lens with the source images (case of a galaxy source).