Measuring Dark Energy Properties with Photometrically Classified Pan-STARRS Supernovae. II. Cosmological Parameters

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractWe use 1169 Pan-STARRS supernovae (SNe) and 195 low-z (z < 0.1) SNe Ia to measure cosmological parameters. Though most Pan-STARRS 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 core-collapse (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 equation-of-state 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 Light-curve Analysis and the Pantheon sample. We try four different photometric classification priors for Pan-STARRS 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, s = 0.012 w CC , is the third-smallest source of systematic uncertainty in this work. We find limited (1.6σ) evidence for evolution of the SN color-luminosity relation with redshift, a possible systematic that could constitute a significant uncertainty in future high-z 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.

Probing the Vacuum Decay Hypothesis with Growth Function Data

“…In agreement with recent studies involving SN Ia, (BAO), CMB and H 0 [35], we also add the constraint Ω m,0 = 0.303 ± 0.007. [47] In order to obtain f theo i , we solve the differential Equation (20) by treating the initial condition f 0 as a nuisance parameter and marginalizing over f 0 .…”

Is it no Longer Necessary to Test Cosmologies with Type Ia Supernovae?

“…Since then over 1200 high-redshift SNeIa with increasing precision have been observed, which confirm this result [11]. This situation is generally explained away by postulating the existence of some unknown component in the energy budget of the universe, termed as "dark energy"-a smoothly pervasive component whose pressure is sufficiently negative.…”

“…Moreover, the new method prohibits an objective assessment of the considered theory in terms of the goodness-of-fit probability P, in the absence of which the estimated parameters do not have any significance. It might be legitimate to consider χ 2 /DoF = 1 for the nearby SNeIa only, for which all the models consistently give the same m − z relation (11). Nevertheless, the high-redshift SNeIa must be checked to be consistent with the model before calculating the confidence intervals on the estimated parameters.…”

“…Many other groups, which were earlier following the conventional methods to analyze the SNeIa data, now follow the new approach [11].…”

Dark Matter Equation of State through Cosmic History

“…Cosmologically, it is usually modeled as cold dark matter (CDM), which is part of the successful ΛCDM model that is consistent with observations of the cosmic microwave background (CMB) (e.g., [8]), cosmic shear surveys (e.g., [9]), measurements of the background expansion such as BAO probes [10], supernovae distance measurements [11], and the observed abundance of light elements [12].…”