ar X iv : a st ro - p h / 96 07 08 4 v 1 1 7 Ju l 1 99 6 Effects of Weak Gravitational Lensing from Large - Scale Structure on the Determination of q 0
نویسندگان
چکیده
Weak gravitational lensing by large-scale structure affects the determination of the cosmological deceleration parameter q0. We find that the lensing induced dispersions on truly standard candles are 0.04 and 0.02 mag at redshift z = 1 and z = 0.5, respectively, in a COBE-normalized cold dark matter universe with Ω0 = 0.40, Λ0 = 0.6, H = 65km/s/Mpc and σ8 = 0.79. It is shown that one would observe q0 = −0.44 +0.17 −0.05 and q0 = −0.45 +0.10 −0.03 (the errorbars are 2σ limits) with standard candles with zero intrinsic dispersion at redshift z = 1 and z = 0.5, respectively, compared to the truth of q0 = −0.40 in this case, i.e., a 10% error in q0 will be made. A standard COBE normalized Ω0 = 1 CDM model would produce three times as much variance and a mixed (hot and cold) dark matter model would lead to an intermediate result. One unique signature of this dispersion effect is its non Gaussianity. Although the lensing induced dispersion at lower redshift is still significantly smaller than the currently best observed (total) dispersion of 0.12 mag in a sample of type Ia supernovae, selected with the multicolor light curve shape method, it becomes significant at higher redshift. We show that there is an optimal redshift, in the range z ∼ 0.5 − 2.0 depending on the amplitude of the intrinsic dispersion of the standard candles, at which q0 can be most accurately determined. Subject headings: Cosmology: large-scale structure of Universe – cosmology: theory – gravitational lensing – numerical method – supernovae
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ar X iv : a st ro - p h / 96 08 06 8 v 1 1 3 A ug 1 99 6 FERMILAB - Pub - 96 / 067 - A Weak Lensing and the Measurement of q
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