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Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples

M. Betoule, R. Kessler, J. Guy, J. Mosher, D. Hardin, R. Biswas, P. Astier, P. El-Hage, M. Konig, S. Kuhlmann, J. Marriner, R. Pain, N. Regnault, C. Balland, B. A. Bassett, P. J. Brown, H. Campbell, R. G. Carlberg, F. Cellier-Holzem, D. Cinabro, A. Conley, C. B. D'Andrea, D. L. DePoy, M. Doi, R. S. Ellis, S. Fabbro, A. V. Filippenko, R. J. Foley, J. A. Frieman, D. Fouchez, L. Galbany, A. Goobar, R. R. Gupta, G. J. Hill, R. Hlozek, C. J. Hogan, I. M. Hook, D. A. Howell, S. W. Jha, L. Le Guillou, G. Leloudas, C. Lidman, J. L. Marshall, A. Möller, A. M. Mourão, J. Neveu, R. Nichol, M. D. Olmstead, N. Palanque-Delabrouille, S. Perlmutter, J. L. Prieto, C. J. Pritchet, M. Richmond, A. G. Riess, V. Ruhlmann-Kleider, M. Sako, K. Schahmaneche, D. P. Schneider, M. Smith, J. Sollerman, M. Sullivan, N. A. Walton, C. J. Wheeler

TL;DR

This study delivers improved cosmological constraints by performing a blind, joint calibration and analysis of SN Ia data from the SDSS-II and SNLS surveys, augmented with the C11 compilation. Using a retrained SALT2 light-curve model and a comprehensive treatment of calibration, bias, and host-mass systematics, the authors construct a robust JLA Hubble diagram for 740 SNe Ia. They find Ω_m = $0.295 \\pm 0.034$ in flat ΛCDM, consistent with Planck, and, when combined with CMB and BAO, a cosmological-constant-like w ≈ −1 with tight uncertainties. The results underscore that calibration dominates the systematic error budget and that future infrared-enabled surveys with refined standards can further sharpen dark energy constraints.

Abstract

We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The data set includes several low-redshift samples (z<0.1), all 3 seasons from the SDSS-II (0.05 < z < 0.4), and 3 years from SNLS (0.2 <z < 1) and totals \ntotc spectroscopically confirmed type Ia supernovae with high quality light curves. We have followed the methods and assumptions of the SNLS 3-year data analysis except for the following important improvements: 1) the addition of the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training of the SALT2 light curve model and in the Hubble diagram analysis (\nsdssc SNe), 2) inter-calibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis, and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN Ia light-curves. We produce recalibrated SN Ia light-curves and associated distances for the SDSS-II and SNLS samples. The large SDSS-II sample provides an effective, independent, low-z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low-z SN sample. For a flat LCDM cosmology we find Omega_m=0.295+-0.034 (stat+sys), a value consistent with the most recent CMB measurement from the Planck and WMAP experiments. Our result is 1.8sigma (stat+sys) different than the previously published result of SNLS 3-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark-energy equation of state parameter w=-1.018+-0.057 (stat+sys) for a flat universe. Adding BAO distance measurements gives similar constraints: w=-1.027+-0.055.

Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples

TL;DR

This study delivers improved cosmological constraints by performing a blind, joint calibration and analysis of SN Ia data from the SDSS-II and SNLS surveys, augmented with the C11 compilation. Using a retrained SALT2 light-curve model and a comprehensive treatment of calibration, bias, and host-mass systematics, the authors construct a robust JLA Hubble diagram for 740 SNe Ia. They find Ω_m = in flat ΛCDM, consistent with Planck, and, when combined with CMB and BAO, a cosmological-constant-like w ≈ −1 with tight uncertainties. The results underscore that calibration dominates the systematic error budget and that future infrared-enabled surveys with refined standards can further sharpen dark energy constraints.

Abstract

We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The data set includes several low-redshift samples (z<0.1), all 3 seasons from the SDSS-II (0.05 < z < 0.4), and 3 years from SNLS (0.2 <z < 1) and totals \ntotc spectroscopically confirmed type Ia supernovae with high quality light curves. We have followed the methods and assumptions of the SNLS 3-year data analysis except for the following important improvements: 1) the addition of the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training of the SALT2 light curve model and in the Hubble diagram analysis (\nsdssc SNe), 2) inter-calibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis, and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN Ia light-curves. We produce recalibrated SN Ia light-curves and associated distances for the SDSS-II and SNLS samples. The large SDSS-II sample provides an effective, independent, low-z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low-z SN sample. For a flat LCDM cosmology we find Omega_m=0.295+-0.034 (stat+sys), a value consistent with the most recent CMB measurement from the Planck and WMAP experiments. Our result is 1.8sigma (stat+sys) different than the previously published result of SNLS 3-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark-energy equation of state parameter w=-1.018+-0.057 (stat+sys) for a flat universe. Adding BAO distance measurements gives similar constraints: w=-1.027+-0.055.

Paper Structure

This paper contains 56 sections, 32 equations, 22 figures, 20 tables.

Table of Contents

  1. Introduction
  2. Data samples
  3. The SDSS-II SN Ia sample
  4. The C11 compilation
  5. Joint photometric calibration of the SNLS and the SDSS-II surveys
  6. The SDSS-II and SNLS supernova surveys
  7. Calibration of photometric measurements
  8. Recalibration of SDSS-II and SNLS supernova light curves
  9. SNLS
  10. SDSS
  11. Uncertainties in the photometric calibration of light curves
  12. Global uncertainties on the flux standards
  13. Uncertainties in the SNLS and SDSS calibration
  14. Uncertainties in the calibration of the low-$z$ sample
  15. Uncertainties in the calibration of HST supernovae
  16. ...and 41 more sections

Figures (22)

  • Figure 1: The difference between aperture and PSF photometry as a function of the SNLS tertiary standard star magnitude. The aperture photometry from B12 has been corrected for residual contamination using an estimate of the local background level obtained with PSF photometry. The magnitude range used in the zero-point fit (vertical dashed lines) is chosen so that the aperture catalog is expected to be free from selection bias [Fig. 12]B12.
  • Figure 2: Comparison of $\mathcal{M}_0$ templates between the previous release of the SALT2 model 2010AA...523A...7G and the present release trained on the JLA sample. Left: The present model is shown as a black dashed line at three different phases: early (-10 days), close to maximum (0 day), and late (+15 days). The 2010AA...523A...7G model is shown as the red solid line. Right: Relative differences in the two models (JLA/G10 - 1) at the three selected phases.
  • Figure 3: Top: Comparison of the reconstructed color law $C_L$ for two trainings of the SALT2 model (see Eq. (\ref{['eq:13']}): the present release trained on the JLA sample (back dashed line) and the previous release of the SALT2 model from 2010AA...523A...7G (red solid line). We display $- 0.1 \log C_L$, which is approximately the rms magnitude variation from color variation. Bottom: Difference in the two color laws.
  • Figure 4: Bias in reconstructed distance modulus as a function of redshift. Simulations follow the color variation model described in 2013arXiv1306.4050S. The simulated sample includes low-$z$, SDSS-II and SNLS SNe Ia and is representative of our JLA sample described in Sect. \ref{['sec:sn-cosmology-sample']}. The analysis of the simulated sample includes the bias correction described in Sect. \ref{['sec:select-bias-corr']} (computed under the baseline SALT2 assumptions). The SALT2 model was not retrained on the simulated sample, similarly to what is done in 2013ApJ...764...48K.
  • Figure 5: Bias corrections computed from Monte Carlo simulations of the cosmological analysis (see Eq. \ref{['eq:11']}). Error bars show the statistical uncertainty of the correction due to MC noise and uncertainty in the selection function. The smallest error bars show the contribution from Monte Carlo noise alone.
  • ...and 17 more figures