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Title:
Improved Dark Energy Constraints from ~100 New CfA Supernova Type Ia Light Curves
Authors:
Hicken, Malcolm; Wood-Vasey, W. Michael; Blondin, Stephane; Challis, Peter; Jha, Saurabh; Kelly, Patrick L.; Rest, Armin; Kirshner, Robert P.
Affiliation:
AA(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA ; Department of Physics, Harvard University, Cambridge, MA 02138, USA ; mhickencfa.harvard.edu ), AB(Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA kirshner@cfa.harvard.edu), AC(European Southern Observatory, D-85748 Garching, Germany ), AD(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA ), AE(Department of Physics and Astronomy, Rutgers, the State University of New Jersey, Piscataway, NJ 08854, USA ), AF(Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USA ), AG(Department of Physics, Harvard University, Cambridge, MA 02138, USA ; Cerro Tololo Inter-American Observatory (CTIO), Colina el Pino S/N, La Serena, Chile), AH(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA )
Publication:
The Astrophysical Journal, Volume 700, Issue 2, pp. 1097-1140 (2009). (ApJ Homepage)
Publication Date:
08/2009
Origin:
IOP
ApJ Keywords:
cosmology: dark energy, supernovae: general
DOI:
10.1088/0004-637X/700/2/1097
Bibliographic Code:
2009ApJ...700.1097H

Abstract

We combine the CfA3 supernovae Type Ia (SN Ia) sample with samples from the literature to calculate improved constraints on the dark energy equation of state parameter, w. The CfA3 sample is added to the Union set of Kowalski et al. to form the Constitution set and, combined with a BAO prior, produces 1 + w = 0.013+0.066 -0.068 (0.11 syst), consistent with the cosmological constant. The CfA3 addition makes the cosmologically useful sample of nearby SN Ia between 2.6 and 2.9 times larger than before, reducing the statistical uncertainty to the point where systematics play the largest role. We use four light-curve fitters to test for systematic differences: SALT, SALT2, MLCS2k2 (RV = 3.1), and MLCS2k2 (RV = 1.7). SALT produces high-redshift Hubble residuals with systematic trends versus color and larger scatter than MLCS2k2. MLCS2k2 overestimates the intrinsic luminosity of SN Ia with 0.7 < Δ < 1.2. MLCS2k2 with RV = 3.1 overestimates host-galaxy extinction while RV ≈ 1.7 does not. Our investigation is consistent with no Hubble bubble. We also find that, after light-curve correction, SN Ia in Scd/Sd/Irr hosts are intrinsically fainter than those in E/S0 hosts by 2σ, suggesting that they may come from different populations. We also find that SN Ia in Scd/Sd/Irr hosts have low scatter (0.1 mag) and reddening. Current systematic errors can be reduced by improving SN Ia photometric accuracy, by including the CfA3 sample to retrain light-curve fitters, by combining optical SN Ia photometry with near-infrared photometry to understand host-galaxy extinction, and by determining if different environments give rise to different intrinsic SN Ia luminosity after correction for light-curve shape and color.
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