Snls3: Constraints on Dark Energy Combining the Supernova Legacy Survey Three-Year Data With Other Probes

Abstract

We present observational constraints on the nature of dark energy using the Supernova Legacy Survey three year sample (SNLS3) of Guy et al. (2010) and Conley et al. -3 -(2011). We use the 472 SNe Ia in this sample, accounting for recently discovered correlations between SN Ia luminosity and host galaxy properties, and include the effects of all identified systematic uncertainties directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and a prior on the Hubble constant H 0 from SHOES, in a flat universe we find Ω m = 0.269 ± 0.015 and w = −1.061 +0.069 −0.068 (where the uncertainties include all statistical and SN Ia systematic errors) -a 6.5% measure of the dark energy equation-of-state parameter w. The statistical and systematic uncertainties are approximately equal, with the systematic uncertainties dominated by the photometric calibration of the SN Ia fluxes -without these calibration effects, systematics contribute only a ∼ 2% error in w. When relaxing the assumption of flatness, we find Ω m = 0.271 ± 0.015, Ω k = −0.002 ± 0.006, and w = −1.069 +0.091 −0.092 . Parameterizing the time evolution of w as w(a) = w 0 + w a (1 − a), gives w 0 = −0.905 ± 0.196, w a = −0.984 +1.094 −1.097 in a flat universe. All of our results are consistent with a flat, w = −1 universe.The size of the SNLS3 sample allows various tests to be performed with the SNe segregated according to their light curve and host galaxy properties. We find that the cosmological constraints derived from these different sub-samples are consistent. There is evidence that the coefficient, β, relating SN Ia luminosity and color, varies with host parameters at > 4σ significance (in addition to the known SN luminosity-host relation); however this has only a small effect on the cosmological results and is currently a subdominant systematic.

Observational probes of cosmic acceleration

“…The most up-to-date analysis is that of Conley et al (2011), who find w = −0.91 +0.16 −0.20 (stat) +0.07 −0.14 (sys) for SNe alone, assuming a flat universe with constant w and marginalizing over Ω m . Combining this measurement with other data sets, Sullivan et al (2011) find w = −1.016 +0.077 −0.079 in combination with 7-year WMAP CMB constraints (similar to the value and error bar quoted above), and w = −1.061 +0.069 −0.068 after adding BAO and H 0 measurements. There are several indications that current SN cosmology studies are limited by systematic uncertainties associated with the linked issues of dust extinction, SN colors, and photometric calibration.…”

“…In the analysis of Wood-Vasey et al (2007), different priors about host galaxy extinction change the inferred value of w by amounts comparable to the statistical error. When the ratio of extinction to reddening is treated as a free parameter in the cosmological fits, the derived values are typically quite far from those measured for Galactic interstellar dust, e.g., R V ≡ A V /E(B − V ) = 1.5 − 2.5 (Hicken et al 2009b;Kessler et al 2009;Sullivan et al 2011) instead of the mean R V = 3.1 found in the diffuse interstellar medium of the Milky Way (Cardelli et al, 1989). This difference could be a reflection of different kinds of dust along the line of sight to the supernova (e.g., circumstellar dust), but it could also arise from intrinsic color differences among SNe Ia with similar light curve shapes, which would reduce the inferred R V if they are assumed to arise from reddening.…”

“…The largest high-redshift (z ≈ 0.4 − 1.0) data sets are those from the ESSENCE survey (Wood-Vasey et al 2007; Narayan et al, in prep. ; ∼200 spectroscopically confirmed Type Ia SNe) and the CFHT Supernova Legacy Survey (SNLS; Astier et al 2006;Conley et al 2011;Sullivan et al 2011; ∼500 spectroscopically confirmed Type Ia SNe in the three-year data set SNLS3). At very high redshifts, HST surveys (Riess et al, 2004Suzuki et al, 2012) have yielded ∼ 25 Type Ia SNe at z > 1.0, which confirm the expectation that the universe was decelerating at high redshift and limit possible systematic effects from evolution of the supernova population or intergalactic dust extinction.…”

Planck2013 results. XVI. Cosmological parameters

“…The likelihood for this sample is then constructed as in Conley et al (2011) and Sullivan et al (2011):…”

How well can the evolution of the scale factor be reconstructed by the current data?

“…where the penalty factor is given by Reconstruction of q(z) We use the SNeIa sample from SNLS3 Sullivan et al 2011) and, thus, the likelihood is build as We use data from Baryon Acoustic Oscillation (BAO) surveys such as WiggleZ, SDSS and 6dFGRS as described in Hinshaw et al (2013). The BAO likelihood is given by…”