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First cosmology results using SNe Ia from the Dark Energy Survey: analysis, systematic uncertainties, and validation

First cosmology results using SNe Ia from the Dark Energy Survey: analysis, systematic uncertainties, and validation
First cosmology results using SNe Ia from the Dark Energy Survey: analysis, systematic uncertainties, and validation

We present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.017 < z < 0.849. We combine the DES-SN sample with an external sample of 122 low-redshift (z < 0.1) SNe Ia, resulting in a "DES-SN3YR" sample of 329 SNe Ia. Our cosmological analyses are blinded: after combining our DES-SN3YR distances with constraints from the Cosmic Microwave Background, our uncertainties in the measurement of the dark energy equation-of-state parameter, w, are 0.042 (stat) and 0.059 (stat+syst) at 68% confidence. We provide a detailed systematic uncertainty budget, which has nearly equal contributions from photometric calibration, astrophysical bias corrections, and instrumental bias corrections. We also include several new sources of systematic uncertainty. While our sample is less than one-third the size of the Pantheon sample, our constraints on w are only larger by 1.4×, showing the impact of the DES-SN Ia light-curve quality. We find that the traditional stretch and color standardization parameters of the DES-SNe Ia are in agreement with earlier SN Ia samples such as Pan-STARRS1 and the Supernova Legacy Survey. However, we find smaller intrinsic scatter about the Hubble diagram (0.077 mag). Interestingly, we find no evidence for a Hubble residual step (0.007 ± 0.018 mag) as a function of host-galaxy mass for the DES subset, in 2.4σ tension with previous measurements. We also present novel validation methods of our sample using simulated SNe Ia inserted in DECam images and using large catalog-level simulations to test for biases in our analysis pipelines.

cosmological parameters, dark energy, supernovae: general
0004-637X
1-30
Brout, D.
2e6c15c6-38ee-4593-b3b6-3c3f406b4fb1
Scolnic, D.
dcdbe5db-52ef-4d69-93d1-3f337046dcfa
Kessler, R.
99f83208-8a92-44e7-9bc0-bd076333095f
Sullivan, Mark
2f31f9fa-8e79-4b35-98e2-0cb38f503850
Childress, Michael
7d0e608c-b9de-4631-bab5-7a2b810a0a2b
et al.
The DES Collaboration
Brout, D.
2e6c15c6-38ee-4593-b3b6-3c3f406b4fb1
Scolnic, D.
dcdbe5db-52ef-4d69-93d1-3f337046dcfa
Kessler, R.
99f83208-8a92-44e7-9bc0-bd076333095f
Sullivan, Mark
2f31f9fa-8e79-4b35-98e2-0cb38f503850
Childress, Michael
7d0e608c-b9de-4631-bab5-7a2b810a0a2b

Brout, D., Scolnic, D. and Kessler, R. , et al. and The DES Collaboration (2019) First cosmology results using SNe Ia from the Dark Energy Survey: analysis, systematic uncertainties, and validation. The Astrophysical Journal, 874 (2), 1-30, [150]. (doi:10.3847/1538-4357/ab08a0).

Record type: Article

Abstract

We present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.017 < z < 0.849. We combine the DES-SN sample with an external sample of 122 low-redshift (z < 0.1) SNe Ia, resulting in a "DES-SN3YR" sample of 329 SNe Ia. Our cosmological analyses are blinded: after combining our DES-SN3YR distances with constraints from the Cosmic Microwave Background, our uncertainties in the measurement of the dark energy equation-of-state parameter, w, are 0.042 (stat) and 0.059 (stat+syst) at 68% confidence. We provide a detailed systematic uncertainty budget, which has nearly equal contributions from photometric calibration, astrophysical bias corrections, and instrumental bias corrections. We also include several new sources of systematic uncertainty. While our sample is less than one-third the size of the Pantheon sample, our constraints on w are only larger by 1.4×, showing the impact of the DES-SN Ia light-curve quality. We find that the traditional stretch and color standardization parameters of the DES-SNe Ia are in agreement with earlier SN Ia samples such as Pan-STARRS1 and the Supernova Legacy Survey. However, we find smaller intrinsic scatter about the Hubble diagram (0.077 mag). Interestingly, we find no evidence for a Hubble residual step (0.007 ± 0.018 mag) as a function of host-galaxy mass for the DES subset, in 2.4σ tension with previous measurements. We also present novel validation methods of our sample using simulated SNe Ia inserted in DECam images and using large catalog-level simulations to test for biases in our analysis pipelines.

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1811.02377 - Accepted Manuscript
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Accepted/In Press date: 11 February 2019
Published date: 2 April 2019
Keywords: cosmological parameters, dark energy, supernovae: general

Identifiers

Local EPrints ID: 429874
URI: http://eprints.soton.ac.uk/id/eprint/429874
ISSN: 0004-637X
PURE UUID: 7a4ab7ad-c8db-4708-8e34-774f4613ee6e
ORCID for Mark Sullivan: ORCID iD orcid.org/0000-0001-9053-4820

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Date deposited: 08 Apr 2019 16:30
Last modified: 07 Oct 2020 02:02

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