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New Constraints on $Ω_M$, $Ω_Λ$, and w from an Independent Set of Eleven High-Redshift Supernovae Observed with HST

R. A. Knop, G. Aldering, R. Amanullah, P. Astier, G. Blanc, M. S. Burns, A. Conley, S. E. Deustua, M. Doi, R. Ellis, S. Fabbro, G. Folatelli, A. S. Fruchter, G. Garavini, S. Garmond, K. Garton, R. Gibbons, G. Goldhaber, A. Goobar, D. E. Groom, D. Hardin, I. Hook, D. A. Howell, A. G. Kim, B. C. Lee, C. Lidman, J. Mendez, S. Nobili, P. E. Nugent, R. Pain, N. Panagia, C. R. Pennypacker, S. Perlmutter, R. Quimby, J. Raux, N. Regnault, P. Ruiz-Lapuente, G. Sainton, B. Schaefer, K. Schahmaneche, E. Smith, A. L. Spadafora, V. Stanishev, M. Sullivan, N. A. Walton, L. Wang, W. M. Wood-Vasey, N. Yasuda

TL;DR

This paper presents eleven high-redshift Type Ia supernovae observed with HST WFPC2, providing high-precision color measurements and per-object host extinction corrections. Using improved color/K-corrections and consistent lightcurve templates, the authors constrain $Ω_M$ and $Ω_Λ$ in a flat universe to $Ω_M ≈ 0.25$ and $Ω_Λ ≈ 0.75$, with robust evidence for dark energy ($P(Ω_Λ>0) ≳ 0.99$). When combined with external CMB and large-scale structure data, they derive $w ≈ -1.05$, consistent with a cosmological constant and with a wide range of dark energy models. The results strengthen the case for a low-density, flat universe dominated by dark energy and demonstrate that precise per-SN extinction corrections are feasible, reducing one of the major systematic uncertainties in SN cosmology.

Abstract

We report measurements of $Ω_M$, $Ω_Λ$, and w from eleven supernovae at z=0.36-0.86 with high-quality lightcurves measured using WFPC-2 on the HST. This is an independent set of high-redshift supernovae that confirms previous supernova evidence for an accelerating Universe. Combined with earlier Supernova Cosmology Project data, the new supernovae yield a flat-universe measurement of the mass density $Ω_M=0.25^{+0.07}_{-0.06}$ (statistical) $\pm0.04$ (identified systematics), or equivalently, a cosmological constant of $Ω_Λ=0.75^{+0.06}_{-0.07}$ (statistical) $\pm0.04$ (identified systematics). When the supernova results are combined with independent flat-universe measurements of $Ω_M$ from CMB and galaxy redshift distortion data, they provide a measurement of $w=-1.05^{+0.15}_{-0.20}$ (statistical) $\pm0.09$ (identified systematic), if w is assumed to be constant in time. The new data offer greatly improved color measurements of the high-redshift supernovae, and hence improved host-galaxy extinction estimates. These extinction measurements show no anomalous negative E(B-V) at high redshift. The precision of the measurements is such that it is possible to perform a host-galaxy extinction correction directly for individual supernovae without any assumptions or priors on the parent E(B-V) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with $P(Ω_Λ>0)>0.99$, a result consistent with previous and current supernova analyses which rely upon the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.

New Constraints on $Ω_M$, $Ω_Λ$, and w from an Independent Set of Eleven High-Redshift Supernovae Observed with HST

TL;DR

This paper presents eleven high-redshift Type Ia supernovae observed with HST WFPC2, providing high-precision color measurements and per-object host extinction corrections. Using improved color/K-corrections and consistent lightcurve templates, the authors constrain and in a flat universe to and , with robust evidence for dark energy (). When combined with external CMB and large-scale structure data, they derive , consistent with a cosmological constant and with a wide range of dark energy models. The results strengthen the case for a low-density, flat universe dominated by dark energy and demonstrate that precise per-SN extinction corrections are feasible, reducing one of the major systematic uncertainties in SN cosmology.

Abstract

We report measurements of , , and w from eleven supernovae at z=0.36-0.86 with high-quality lightcurves measured using WFPC-2 on the HST. This is an independent set of high-redshift supernovae that confirms previous supernova evidence for an accelerating Universe. Combined with earlier Supernova Cosmology Project data, the new supernovae yield a flat-universe measurement of the mass density (statistical) (identified systematics), or equivalently, a cosmological constant of (statistical) (identified systematics). When the supernova results are combined with independent flat-universe measurements of from CMB and galaxy redshift distortion data, they provide a measurement of (statistical) (identified systematic), if w is assumed to be constant in time. The new data offer greatly improved color measurements of the high-redshift supernovae, and hence improved host-galaxy extinction estimates. These extinction measurements show no anomalous negative E(B-V) at high redshift. The precision of the measurements is such that it is possible to perform a host-galaxy extinction correction directly for individual supernovae without any assumptions or priors on the parent E(B-V) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with , a result consistent with previous and current supernova analyses which rely upon the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.

Paper Structure

This paper contains 24 sections, 5 equations, 17 figures, 28 tables.

Table of Contents

  1. Introduction
  2. Observations, Data Reduction, and Analysis
  3. WFPC2 Photometry
  4. Lightcurve Fits
  5. Color- and $K$-Corrections
  6. Cosmological Fit Methodology
  7. Supernova Subsets
  8. Colors and Extinction
  9. Cosmological Results
  10. $\Omega_\mathrm{M}$ and $\Omega_\Lambda$
  11. Combined High-Redshift Supernova Measurements
  12. Dark Energy Equation of State
  13. Systematic Errors
  14. Fit Method, Subset Selection, and Choice of $\alpha$
  15. Non-Type Ia Supernova Contamination
  16. ...and 9 more sections

Figures (17)

  • Figure 1: Lightcurves and images from the PC CCD on WFPC2 for the HST supernovae reported in this paper. The left column shows the $R$-band (including F675W HST data), and the middle column shows $I$-band lightcurves (including F814W HST data). Open circles represent ground-based data points, and filled circles represent WFPC2 data points. Note that there are correlated errors between all of the ground-based points for each supernova in these figures, as a single ground-based zeropoint was used to scale each of them together with the HST photometry. The right column shows $6"\times6"$ images, summed from all HST images of the supernova in the indicated filter.
  • Figure 2: Lightcurves and images from the PC CCD on WFPC2 for the HST supernovae reported in this paper (continued). The left column shows the $R$-band (including F675W HST data), and the middle column shows $I$-band lightcurves (including F814W HST data). Open circles represent ground-based data points, and filled circles represent WFPC2 data points. Note that there are correlated errors between all of the ground-based points for each supernova in these figures, as a single ground-based zeropoint was used to scale each of them together with the HST photometry. The right column shows $6"\times6"$ images, summed from all HST images of the supernova in the indicated filter.
  • Figure 3: Supernova Lightcurve Fits: HST Supernovae from this paper
  • Figure 4: Supernova Lightcurve Fits: New Fits to Perlmutter (1999) SNe
  • Figure 5: Supernova Lightcurve Fits: Low-z SNe from Hamuy (1996) and Riess (1999)
  • ...and 12 more figures