Cosmological parameter extraction and biases from type Ia supernova magnitude evolution
Abstract
We study different oneparametric models of type Ia supernova magnitude evolution on cosmic time scales. Constraints on cosmological and supernova evolution parameters are obtained by combined fits on the actual data coming from supernovae, the cosmic microwave background, and baryonic acoustic oscillations. We find that the bestfit values imply supernova magnitude evolution such that highredshift supernovae appear some percent brighter than would be expected in a standard cosmos with a dark energy component. However, the errors on the evolution parameters are of the same order, and data are consistent with nonevolving magnitudes at the 1σ level, except for special cases. We simulate a future data scenario where SN magnitude evolution is allowed for, and neglect the possibility of such an evolution in the fit. We find the fiducial models for which the wrong model assumption of nonevolving SN magnitude is not detectable, and for which biases on the fitted cosmological parameters are introduced at the same time. Of the cosmological parameters, the overall mass density Ω_{M} has the strongest chances to be biased due to the wrong model assumption. Whereas earlyepoch models with a magnitude offset ∆ m∼ z^{2} show up to be not too dangerous when neglected in the fitting procedure, late epoch models with ∆ m∼√{z} have high chances of undetectably biasing the fit results.
Centre de Physique Théorique is UMR 6207  “Unité Mixte de Recherche” of CNRS and of the Universities “de Provence”, “de la Mediterranée”, and “du Sud ToulonVar”  Laboratory affiliated with FRUMAM (FR2291).
 Publication:

Astronomy and Astrophysics
 Pub Date:
 November 2009
 DOI:
 10.1051/00046361/200912811
 arXiv:
 arXiv:0907.4495
 Bibcode:
 2009A&A...506.1095L
 Keywords:

 cosmology: cosmological parameters;
 cosmology: observations;
 stars: supernovae: general;
 surveys;
 Astrophysics  Cosmology and Extragalactic Astrophysics
 EPrint:
 12 pages, 5 figures, 3 tables. Accepted for publication by A&