Significant effects of weak gravitational lensing on determinations of the cosmology from Type Ia supernovae

Significant adjustments to the values of the cosmological parameters estimated from high-redshift Type Ia supernovae data are reported, almost an order of magnitude greater than previously found. They arise from the effects of weak gravitational lensing on observations of high-redshift sources. The lensing statistics used have been obtained from computations of the three-dimensional shear in a range of cosmological N-body simulations, from which it is estimated that cosmologies with an underlying deceleration parameter q(0) = -0.51(-0.24)(+0.03) may be interpreted as having q(0) = -0.55 (appropriate to the currently popular cosmology with density parameter Omega(M) = 0.3 and vacuum energy density parameter Omega(Lambda) = 0.7). In addition, the standard deviation expected from weak lensing for the peak magnitudes of Type Ia supernovae at redshifts of z = 1 is expected to be approximately 0.078 mag, and 0.185 mag at redshift z = 2. This latter value is greater than the accepted intrinsic dispersion of 0.17 mag. Consequently, the effects of weak lensing in observations of high-redshift sources must be taken properly into account.