Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples (1401.4064v2)

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.

• The paper presents a joint analysis of SDSS-II and SNLS Type Ia supernovae to precisely measure cosmological parameters like Ωm ≈ 0.295 and w ≈ -1.
• It leverages an enhanced SALT2 light-curve model and intercalibrated data to reduce systematic errors and achieve consistency with CMB observations.
• The refined recalibration sets a new standard in photometric accuracy, paving the way for future dark energy research and next-generation surveys.

Cosmological Constraints from Joint Analysis of SNLS and SDSS SN Ia Samples

The paper authored by M. Betoule and collaborators presents a significant advancement in the field of observational cosmology. By conducting a joint analysis of Type Ia supernova (SN Ia) observations from the SDSS-II and SNLS collaborations, the paper enhances our understanding of cosmological parameters with improved precision. The focus on SN Ia as standard candles provides critical insights into the accelerating expansion of the universe, driven by dark energy. Herein, we explore the methodologies, results, and implications of this comprehensive paper.

Data and Methodology

The research leverages a substantial dataset composed of 740 spectroscopically confirmed SNe Ia, integrating several low-redshift samples, three seasons from the SDSS-II survey ($0.05 < z < 0.4$), and three years from SNLS ($0.2 < z < 1$). Key enhancements to the SNLS three-year analysis include:

1. Incorporation of the full SDSS-II sample for training the SALT2 light-curve model and Hubble diagram analysis.
2. Intercalibration of SNLS and SDSS surveys to reduce systematic uncertainties and improve photometric calibration.
3. Extensive investigation of systematic errors linked to the SALT2 modeling process.

These improvements facilitate the recalibration of SN Ia light curves, thereby refining distance calculations crucial for cosmological analysis.

Key Results

The recalibrated dataset provides robust cosmological constraints, demonstrating consistency with the Cosmic Microwave Background (CMB) measurements from Planck and WMAP experiments. Specifically, the analysis yields $\Omega_m = 0.295$ in a flat $\Lambda$CDM model. This value aligns with the CMB data and reduces the systematic errors associated with low-z SN samples. Notably, the paper also measures a dark-energy equation of state parameter $w = -1.018$ when combined with CMB constraints, indicating strong constraints on dark energy characteristics.

Implications and Future Directions

The joint analysis underscores the potential of SN Ia as precise cosmological tools for probing the universe's expansion history. The recalibration efforts align cosmic measurements across different surveys, setting a new standard for photometric accuracy. This enhanced precision paves the way for future experiments and surveys, such as DES and LSST, which can further explore dark energy models and refine cosmological parameters.

Moreover, the findings stimulate further investigation into potential systematics affecting SN Ia observations, such as host galaxy properties and intrinsic scatter in SN luminosity. The research highlights the importance of comprehensive error modeling and recalibration in reducing systematic discrepancies across diverse observational datasets.

In conclusion, this paper contributes a major milestone in cosmological studies, offering improved methodologies and insights into the nature of dark energy. The effective combination of SNLS and SDSS data sets a precedent for future collaborative efforts in the cosmology community, enhancing our understanding of the fundamental parameters governing the universe.