The Complete Light-curve Sample of Spectroscopically Confirmed Type Ia Supernovae from Pan-STARRS1 and Cosmological Constraints from The Combined Pantheon Sample (1710.00845v3)

Abstract: We present optical light curves, redshifts, and classifications for 365 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered by the Pan-STARRS1 (PS1) Medium Deep Survey. We detail improvements to the PS1 SN photometry, astrometry and calibration that reduce the systematic uncertainties in the PS1 SN Ia distances. We combine the subset of 279 PS1 SN Ia ($0.03 < z < 0.68$) with useful distance estimates of SN Ia from SDSS, SNLS, various low-z and HST samples to form the largest combined sample of SN Ia consisting of a total of 1048 SN Ia ranging from $0.01 < z < 2.3$, which we call the `Pantheon Sample'. When combining Planck 2015 CMB measurements with the Pantheon SN sample, we find $\Omega_m=0.307\pm0.012$ and $w = -1.026\pm0.041$ for the wCDM model. When the SN and CMB constraints are combined with constraints from BAO and local H0 measurements, the analysis yields the most precise measurement of dark energy to date: $w0 = -1.007\pm 0.089$ and $wa = -0.222 \pm0.407$ for the w0waCDM model. Tension with a cosmological constant previously seen in an analysis of PS1 and low-z SNe has diminished after an increase of $2\times$ in the statistics of the PS1 sample, improved calibration and photometry, and stricter light-curve quality cuts. We find the systematic uncertainties in our measurements of dark energy are almost as large as the statistical uncertainties, primarily due to limitations of modeling the low-redshift sample. This must be addressed for future progress in using SN Ia to measure dark energy.

• The paper presents a comprehensive analysis of 365 SNe Ia light curves from the PS1 data and the Pantheon sample to constrain dark energy parameters.
• It employs refined photometry, calibration methods, and BBC bias corrections to reduce systematic uncertainties in cosmological measurements.
• The research confirms enhanced dataset consistency, narrowing tensions with the cosmological constant and setting a benchmark for future surveys.

An Expert Overview of the Cosmological Insights from Scolnic et al.

The paper by Scolnic et al., titled "The Complete Light-curve Sample of Spectroscopically Confirmed Type Ia Supernovae from Pan-STARRS1 and Cosmological Constraints from The Combined Pantheon Sample," presents an extensive analysis of Type Ia supernovae (SNe Ia) data, emphasizing its implications for cosmological parameters, particularly dark energy. This work is anchored on the Pan-STARRS1 (PS1) Medium Deep Survey data and integrates it with other SN datasets to constrain cosmological models.

Dataset and Methodology

The paper combines optical light curves, redshifts, and classifications for 365 spectroscopically confirmed SNe Ia. A total of 279 PS1 SNe Ia, within redshifts $0.03 < z < 0.68$, complement other samples (e.g., SDSS, SNLS, low-$z$, and HST) to form the "Pantheon Sample," comprising 1048 SNe Ia from redshifts $0.01 < z < 2.3$. This aggregation aims to improve the precision of cosmological measurements by expanding the statistics and reducing systematic uncertainties related to supernova distances.

The methodological framework employed includes refined techniques for photometry and calibration within the PS1 survey. Systematic uncertainties are substantially minimized owing to updates in the PS1 SN photometry, astrometry, and calibration. Additionally, the authors adopt the BEAMS with Bias Corrections (BBC) methodology which, coupled with extensive simulations, addresses the nuisance parameters $\alpha$ (related to stretch) and $\beta$ (related to color), thereby refining the distance estimates.

Key Findings

1. Dark Energy Constraints: Incorporating Planck 2015 CMB measurements, the paper notes $\Omega_m=0.307$ and $w=-1.026$ for the $\Lambda$CDM model. With additional BAO and local $H_0$ constraints, the authors achieve precise constraints on dark energy, showing $w_0=-1.007$ and $w_a=-0.222$.
2. Systematic versus Statistical Uncertainties: The research acknowledges that systematic uncertainties in the dark energy parameter measurement rival the statistical uncertainties, largely due to challenges in modeling the low-redshift sample. This underscores the persistent difficulty in photometric calibration across various SN surveys.
3. Cosmological Constant Tension: Tension with a cosmological constant, previously seen in certain SN analyses, has diminished after the increase in PS1 sample statistics and improvements in calibration and light-curve quality.
4. Consistency and Accuracy: The analysis reaffirms a high level of consistency and calibration homogeneity across the Pantheon compilation, a significant advance considering the calibration has previously been a dominant source of systematic error.

Implications and Future Directions

In the broader context of cosmology, the Pantheon sample's integration and subsequent analytic strategies suggest future pathways for the understanding of dark energy and the universe's expansion history. The precision achieved underscores the potential of current and upcoming large-scale surveys, such as the Vera C. Rubin Observatory's LSST or the Roman Space Telescope, to further tighten constraints on cosmological models.

The paper's emphasis on calibrating across multiple systems indicates an avenue for improving absolute photometry using next-generation instrumentations. There's also an implicit call for more data at both ends of the redshift spectrum—to resolve discrepancies at low $z$ and fully leverage SN observations at high $z$, potentially informing the next iteration of supernova model training.

In conclusion, Scolnic et al.'s work presents a comprehensive approach to reducing systematic uncertainties in supernova cosmology, positioning the Pantheon sample as a robust dataset for contemporary and future investigations into the universe's expansion dynamics. This research continues to play a crucial role in painting a coherent picture of our cosmological landscape and the mysteries that lie within dark energy.