The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample (1105.3470v1)

Abstract: We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe Ia pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Ten of our new SNe Ia are beyond redshift $z=1$, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count rates appropriate for very distant SNe Ia. Adding these supernovae improves the best combined constraint on the dark energy density \rho_{DE}(z) at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe, we find \Omega_\Lambda = 0.724 +0.015/-0.016 (68% CL including systematic errors). For a flat wCDM model, we measure a constant dark energy equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark energy is allowed to vary with parameters w_0 and w_a. Tightening further the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z>1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST.

• The paper demonstrates that including 20 new high-redshift SNe Ia improves dark energy constraints by 18% for the z range 1.0 to 1.6.
• It employs HST ACS and NICMOS observations alongside Keck AO-assisted photometry to address SN Ia luminosity and host mass correlations.
• The research enhances the yield of early-type hosted supernovae, offering valuable insights for future high-redshift SNe Ia survey strategies.

Improving Dark Energy Constraints Using High-Redshift Type Ia Supernovae

The paper "The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above $z > 1$ and Building an Early-Type-Hosted Supernova Sample" presents an in-depth paper leveraging Type Ia supernovae (SNe Ia) discovered through the Hubble Space Telescope (HST) to refine our understanding of dark energy. This research primarily focuses on SNe Ia at redshifts $z >1$ and aims to build a substantial sample of early-type-hosted supernovae.

Study Overview

This research is part of the broader HST Cluster Supernova Survey, with the specific goal of enhancing constraints on dark energy parameters in the $z > 1$ regime. The paper used observations from the ACS and NICMOS instruments on HST, along with Keck AO-assisted photometry. A sample of 20 new SNe Ia was analyzed, which significantly improves the statistical weight of high-redshift supernovae observations.

Key aspects of the analysis include correcting for the correlation between SN Ia luminosity and host galaxy mass and addressing potential NICMOS zeropoint issues at the observed count rates for distant supernovae. By introducing these corrections, the paper claims an 18% improvement in constraining dark energy density for redshifts $1.0 < z < 1.6$ upon combining these SNe Ia with a global compilation of supernovae data.

Numerical Findings

• Cosmological Parameters: The inclusion of these high-redshift SNe Ia in the cosmological analysis supports a flat $\Lambda$CDM model with a dark energy density parameter ($\Omega_{\Lambda}$) refined with systematic errors. In a flat $w$CDM model, the constant dark energy equation of state parameter measured $w = -0.993$ with combined data sets, including CMB and BAO constraints.
• Early-Type Hosted SNe Ia: The survey design, targeting galaxy clusters, enhanced the yield of early-type hosted supernovae by a factor of approximately four, providing insights into galaxy evolution and SNe Ia host properties at high redshifts.

Implications and Future Directions

The paper highlights the practical benefits of cluster-targeted SNe Ia surveys in increasing both the discovery rate and the fraction of early-type hosted supernovae above redshift $z=1$. These high-redshift supernovae are crucial for constraining the time evolution of dark energy, providing a larger baseline for redshift measurements. The improved statistical weight from these new observations enhances our empirical constraints on the dark energy equation-of-state parameter.

Future work will likely focus on increasing the precision of high-redshift SNe Ia observations using newer instruments like the WFC3 on HST, which could further reduce statistical uncertainties. Additionally, improving systematic errors related to SN Ia data calibration, host galaxy properties, and environmental factors will be essential. The inclusion of a more extensive sample of $z>1$ supernovae, balanced across host types, will facilitate these refinements and further elucidate the nature of dark energy.

This paper represents a significant step in leveraging high-redshift supernovae to advance cosmological research, providing a robust framework for both current and forthcoming observational campaigns aimed at unraveling the mysteries of cosmic acceleration.