ZTF SN Ia DR2: Improved SN Ia colors through expanded dimensionality with SALT3+

Context. Type Ia supernovae (SNe Ia) are a key probe in modern cosmology, as they can be used to measure luminosity distances at gigaparsec scales. Models of their light curves are used to project heterogeneous observed data onto a common basis for analysis. Aims. The SALT model currently used for SN Ia cosmology describes SNe as having two sources of variability, accounted for by a color parameter c , and a “stretch” parameter x 1 . We extend the model to include an additional parameter we label x 2 , to investigate the cosmological impact of currently unaddressed light-curve variability. Methods. We constructed a new SALT model, that we dub “SALT3+”. This model was trained by an improved version of the SALTshaker code, using training data combining a selection of the second data release of cosmological SNe Ia from the Zwicky Transient Facility and the existing SALT3 training compilation. Results. We find additional, coherent variability in supernova light curves beyond SALT3. Most of this variation can be described as phase-dependent variation in g − r and r − i color curves, correlated with a boost in the height of the secondary maximum in i -band. These behaviors correlate with spectral differences, particularly in line velocity. We find that fits with the existing SALT3 model tend to address this excess variation with the color parameter, leading to less informative measurements of supernova color. We find that neglecting the new parameter in light-curve fits leads to a trend in Hubble residuals with x 2 of 0.039 ± 0.005 mag, representing a potential systematic uncertainty. However, we find no evidence of a bias in current cosmological measurements. Conclusions. We conclude that extended SN Ia light-curve models promise mild improvement in the accuracy of color measurements, and corresponding cosmological precision. However, models with more parameters are unlikely to substantially affect current cosmological results.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-03-25
DOI
https://doi.org/10.1051/0004-6361/202452578
Citations
1
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
1.15

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article

ZTF SN Ia DR2: Improved SN Ia colors through expanded dimensionality with SALT3+

T.E Müller-Bravo, D. O. Jones, K. Maguire, J. Terwel et al.
1 citations
Astronomy and Astrophysics
Gamma-ray bursts and supernovae
1.15
article

ZTF SN Ia DR2: Improved SN Ia colors through expanded dimensionality with SALT3+

T.E Müller-Bravo, D. O. Jones, K. Maguire, J. Terwel, G. Dimitriadis, P. J. Pessi, L. Galbany, Alan R. Townsend, M Ginolin, J. Nordin, A. Goobar, Suhail Dhawan, W. D. Kenworthy, P. Rosnet, M. Rigault, Josiah Purdum, J Sollerman, P. Nugent, J. Johansson, B. Rusholme, R.R Laher, B Popovic, U. Burgaz, Y.-L Kim, R Kessler, Steven R. Thorp, D. Rosselli
article en
1 citations

Abstract

Context. Type Ia supernovae (SNe Ia) are a key probe in modern cosmology, as they can be used to measure luminosity distances at gigaparsec scales. Models of their light curves are used to project heterogeneous observed data onto a common basis for analysis. Aims. The SALT model currently used for SN Ia cosmology describes SNe as having two sources of variability, accounted for by a color parameter c , and a “stretch” parameter x 1 . We extend the model to include an additional parameter we label x 2 , to investigate the cosmological impact of currently unaddressed light-curve variability. Methods. We constructed a new SALT model, that we dub “SALT3+”. This model was trained by an improved version of the SALTshaker code, using training data combining a selection of the second data release of cosmological SNe Ia from the Zwicky Transient Facility and the existing SALT3 training compilation. Results. We find additional, coherent variability in supernova light curves beyond SALT3. Most of this variation can be described as phase-dependent variation in g − r and r − i color curves, correlated with a boost in the height of the secondary maximum in i -band. These behaviors correlate with spectral differences, particularly in line velocity. We find that fits with the existing SALT3 model tend to address this excess variation with the color parameter, leading to less informative measurements of supernova color. We find that neglecting the new parameter in light-curve fits leads to a trend in Hubble residuals with x 2 of 0.039 ± 0.005 mag, representing a potential systematic uncertainty. However, we find no evidence of a bias in current cosmological measurements. Conclusions. We conclude that extended SN Ia light-curve models promise mild improvement in the accuracy of color measurements, and corresponding cosmological precision. However, models with more parameters are unlikely to substantially affect current cosmological results.

Astronomy and AstrophysicsVol. 697
Université Claude Bernard Lyon 1 (FR), California Institute of Technology (US), Centre National de la Recherche Scientifique (FR), Institute of Space Sciences (ES), Lawrence Berkeley National Laboratory (US), Stockholm University (SE), Lyon College (US), Université Clermont Auvergne (FR), Trinity College Dublin (IE), Aix-Marseille Université (FR), University of Cambridge (GB), University of Hawaii at Hilo (US), Humboldt-Universität zu Berlin (DE), University of Chicago (US), Institut d'Estudis Espacials de Catalunya (ES), Centre de physique des particules de Marseille (FR), Nordic Optical Telescope (ES), Institute of Nuclear Physics of Lyon (FR), Institut de Physique des 2 Infinis de Lyon (FR), Lancaster University (GB), University of California, Berkeley (US)
National Science Foundation, U.S. Department of Energy, California Institute of Technology, University of Washington, European Commission, Weizmann Institute of Science, Knut och Alice Wallenbergs Stiftelse, Vetenskapsrådet, Ministerio de Ciencia e Innovación, Stockholms Universitet, Horizon 2020 Framework Programme, Research Computing Center, University of Chicago, Science and Technology Facilities Council, European Research Council, Deutsches Elektronen-Synchrotron, Agència de Gestió d'Ajuts Universitaris i de Recerca, Agencia Estatal de Investigación, H2020 European Research Council
Openalex Percentile: Top 21%
Gamma-ray bursts and supernovae
1.15
DOIOpen Access PDFOpenAlex
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