Weak lensing of the high redshift SNIa sample

Abstract

The current sample of high-redshift Supernova Type Ia, which combines results from two teams, High-z Supernova Search Team and Supernova Cosmology Project, is analyzed for the effects of weak lensing. After correcting SNe magnitudes for cosmological distances, assuming recently published, homogeneous distance and error estimates, we find that brighter SNe are preferentially found behind regions (5-15 arcmin radius) which are overdense in foreground, z~0.1 galaxies. This is consistent with the interpretation that SNe fluxes are magnified by foreground galaxy excess, and demagnified by foreground galaxy deficit, compared to a smooth Universe case. The difference between most magnified and most demagnified SNe is about 0.3-0.4 mag. The effect is significant at >99% level. Simple modeling reveals that the slope of the relation between SN magnitude and foreground galaxy density depends on the amount and distribution of matter along the line of sight to the sources, but does not depend on the specifics of the galaxy biasing scheme.