Measuring Dark Energy Properties with Photometrically Classified PanSTARRS Supernovae. II. Cosmological Parameters
Abstract
We use 1169 PanSTARRS supernovae (SNe) and 195 lowz (z < 0.1) SNe Ia to measure cosmological parameters. Though most PanSTARRS SNe lack spectroscopic classifications, in a previous paper we demonstrated that photometrically classified SNe can be used to infer unbiased cosmological parameters by using a Bayesian methodology that marginalizes over corecollapse (CC) SN contamination. Our sample contains nearly twice as many SNe as the largest previous SN Ia compilation. Combining SNe with cosmic microwave background (CMB) constraints from Planck, we measure the dark energy equationofstate parameter w to be 0.989 ± 0.057 (stat+sys). If w evolves with redshift as w(a) = w _{0} + w _{ a }(1  a), we find w _{0} = 0.912 ± 0.149 and w _{ a } = 0.513 ± 0.826. These results are consistent with cosmological parameters from the Joint Lightcurve Analysis and the Pantheon sample. We try four different photometric classification priors for PanSTARRS SNe and two alternate ways of modeling CC SN contamination, finding that no variant gives a w differing by more than 2% from the baseline measurement. The systematic uncertainty on w due to marginalizing over CC SN contamination, {σ }_{w}^{CC}}=0.012, is the thirdsmallest source of systematic uncertainty in this work. We find limited (1.6σ) evidence for evolution of the SN colorluminosity relation with redshift, a possible systematic that could constitute a significant uncertainty in future highz analyses. Our data provide one of the best current constraints on w, demonstrating that samples with ∼5% CC SN contamination can give competitive cosmological constraints when the contaminating distribution is marginalized over in a Bayesian framework.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2018
 DOI:
 10.3847/15384357/aab6b1
 arXiv:
 arXiv:1710.00846
 Bibcode:
 2018ApJ...857...51J
 Keywords:

 cosmology: observations;
 dark energy;
 supernovae: general;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted by ApJ, data release at archive.stsci.edu/prepds/ps1cosmo/index.html