Problems with small area surveys: lensing covariance of supernova distance measurements.
While luminosity distances from type Ia supernovae (SNe) are a powerful probe of cosmology, the accuracy with which these distances can be measured is limited by cosmic magnification due to gravitational lensing by the intervening large-scale structure. Spatial clustering of foreground mass leads to correlated errors in SNe distances. By including the full covariance matrix of SNe, we show that future wide-field surveys will remain largely unaffected by lensing correlations. However, "pencil beam" surveys, and those with narrow (but possibly long) fields of view, can be strongly affected. For a survey with 30 arcmin mean separation between SNe, lensing covariance leads to a approximately 45% increase in the expected errors in dark energy parameters.
Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, California 92697, USA.
Asantha
A
Cooray
Dragan
D
Huterer
Daniel E
DE
Holz