ZTF SN Ia DR2: Environmental dependencies of stretch and luminosity for a volume-limited sample of 1000 type Ia supernovae

Context. Type Ia supernova (SN Ia) cosmology studies will soon be dominated by systematic, uncertainties, rather than statistical ones. Thus, it is crucial to understand the unknown phenomena potentially affecting their luminosity that may remain, such as astrophysical biases. For their accurate application in such studies, SN Ia magnitudes need to be standardised; namely, they must be corrected for their correlation with the light-curve width and colour. Aims. Here, we investigate how the standardisation procedure used to reduce the scatter of SN Ia luminosities is affected by their environment. Our aim is to reduce scatter and improve the standardisation process. Methods. We first studied the SN Ia stretch distribution, as well as its dependence on environment, as characterised by local and global ( g − z ) colour and stellar mass. We then looked at the standardisation parameter, α , which accounts for the correlation between residuals and stretch, along with its environment dependency and linearity. Finally, we computed the magnitude offsets between SNe in different astrophysical environments after the colour and stretch standardisations (i.e. steps). This analysis has been made possible thanks to the unprecedented statistics of the volume-limited Zwicky Transient Facility (ZTF) SN Ia DR2 sample. Results. The stretch distribution exhibits a bimodal behaviour, as previously found in the literature. However, we find the distribution to be dependent on environment. Specifically, the mean stretch modes decrease with host stellar mass, at a 9.2 σ significance. We demonstrate, at the 13.4 σ level, that the stretch-magnitude relation is non-linear, challenging the usual linear stretch-residuals relation currently used in cosmological analyses. In fitting for a broken- α model, we did indeed find two different slopes between stretch regimes ( x 1 ≶ x 1 0 with x 1 0 = −0.48 ± 0.08): α low = 0.271 ± 0.011 and α high = 0.083 ± 0.009, comprising a difference of Δ α = −0.188 ± 0.014. As the relative proportion of SNe Ia in the high-stretch and low-stretch modes evolves with redshift and environment, this implies that a single-fitted α also evolves with the redshift and environment. Concerning the environmental magnitude offset γ , we find it to be greater than 0.12 mag, regardless of the considered environmental tracer used (local or global colour and stellar mass), all measured at the ≥5 σ level. When accounting for the non-linearity of the stretch, these steps increase to ∼0.17 mag, measured with a precision of 0.01 mag. Such strong results highlight the importance of using a large volume-limited dataset to probe the underlying SN Ia-host correlations.

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Journal
Astronomy and Astrophysics
Published
2025-03-01
DOI
https://doi.org/10.1051/0004-6361/202450378
Citations
13
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
15.01

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article

ZTF SN Ia DR2: Environmental dependencies of stretch and luminosity for a volume-limited sample of 1000 type Ia supernovae

Ludovic Lacroix, Magali Aubert, K. Maguire, J. Terwel et al.
13 citations
Astronomy and Astrophysics
Gamma-ray bursts and supernovae
15.01
article

ZTF SN Ia DR2: Environmental dependencies of stretch and luminosity for a volume-limited sample of 1000 type Ia supernovae

Ludovic Lacroix, Magali Aubert, K. Maguire, J. Terwel, G. Dimitriadis, F. Ruppin, L. Galbany, F.J Masci, M Ginolin, M. R. Smith, J. Nordin, Y. Copin, T. E. Müller-Bravo, M. Betoule, A. Goobar, F. Feinstein, Alice Townsend, W. D. Kenworthy, J. Sollerman, P. Rosnet, M. Kowalski, M. Rigault, D. Fouchez, S. R. Kulkarni, Thomas de Jaeger, Serene Dhawan, L. Harvey, P. Nugent, Eric C. Bellm, Bastien Carreres, M. Amenouche, J. Johansson, Deanna Kuhn, R.R Laher, B Popovic, U. Burgaz, M. Deckers, C Barjou-Delayre, C Ganot, M. M. Kasliwal, B. Racine, Y.-L Kim, Joël Brugger, R.L Riddle, Y Sharma, D. Rosselli
article en
13 citations

Abstract

Context. Type Ia supernova (SN Ia) cosmology studies will soon be dominated by systematic, uncertainties, rather than statistical ones. Thus, it is crucial to understand the unknown phenomena potentially affecting their luminosity that may remain, such as astrophysical biases. For their accurate application in such studies, SN Ia magnitudes need to be standardised; namely, they must be corrected for their correlation with the light-curve width and colour. Aims. Here, we investigate how the standardisation procedure used to reduce the scatter of SN Ia luminosities is affected by their environment. Our aim is to reduce scatter and improve the standardisation process. Methods. We first studied the SN Ia stretch distribution, as well as its dependence on environment, as characterised by local and global ( g − z ) colour and stellar mass. We then looked at the standardisation parameter, α , which accounts for the correlation between residuals and stretch, along with its environment dependency and linearity. Finally, we computed the magnitude offsets between SNe in different astrophysical environments after the colour and stretch standardisations (i.e. steps). This analysis has been made possible thanks to the unprecedented statistics of the volume-limited Zwicky Transient Facility (ZTF) SN Ia DR2 sample. Results. The stretch distribution exhibits a bimodal behaviour, as previously found in the literature. However, we find the distribution to be dependent on environment. Specifically, the mean stretch modes decrease with host stellar mass, at a 9.2 σ significance. We demonstrate, at the 13.4 σ level, that the stretch-magnitude relation is non-linear, challenging the usual linear stretch-residuals relation currently used in cosmological analyses. In fitting for a broken- α model, we did indeed find two different slopes between stretch regimes ( x 1 ≶ x 1 0 with x 1 0 = −0.48 ± 0.08): α low = 0.271 ± 0.011 and α high = 0.083 ± 0.009, comprising a difference of Δ α = −0.188 ± 0.014. As the relative proportion of SNe Ia in the high-stretch and low-stretch modes evolves with redshift and environment, this implies that a single-fitted α also evolves with the redshift and environment. Concerning the environmental magnitude offset γ , we find it to be greater than 0.12 mag, regardless of the considered environmental tracer used (local or global colour and stellar mass), all measured at the ≥5 σ level. When accounting for the non-linearity of the stretch, these steps increase to ∼0.17 mag, measured with a precision of 0.01 mag. Such strong results highlight the importance of using a large volume-limited dataset to probe the underlying SN Ia-host correlations.

Astronomy and AstrophysicsVol. 695
Université Claude Bernard Lyon 1 (FR), California Institute of Technology (US), Herzberg Institute of Astrophysics (CA), Centre National de la Recherche Scientifique (FR), Institute of Space Sciences (ES), Lawrence Berkeley National Laboratory (US), Stockholm University (SE), Duke University (US), Lyon College (US), Université Clermont Auvergne (FR), University of Washington (US), Trinity College Dublin (IE), Aix-Marseille Université (FR), University of Cambridge (GB), Deutsches Elektronen-Synchrotron DESY (DE), Humboldt-Universität zu Berlin (DE), Sorbonne Université (FR), Institut d'Estudis Espacials de Catalunya (ES), Centre de physique des particules de Marseille (FR), Laboratoire de Physique Nucléaire et de Hautes Énergies (FR), Nordic Optical Telescope (ES), Institute of Nuclear Physics of Lyon (FR), Infrared Processing and Analysis Center (US), Institut de Physique des 2 Infinis de Lyon (FR), City University of Seattle (US), Université Paris 1 Panthéon-Sorbonne (FR), Lancaster University (GB), University of California, Berkeley (US)
National Science Foundation, California Institute of Technology, Northwestern University, University of Washington, University of Warwick, European Commission, Trinity College Dublin, Agence Nationale de la Recherche, Weizmann Institute of Science, Irish Research Council, Generalitat de Catalunya, Knut och Alice Wallenbergs Stiftelse, Vetenskapsrådet, Ministerio de Ciencia e Innovación, Stockholms Universitet, Horizon 2020 Framework Programme, Science and Technology Facilities Council, European Research Council, Deutsches Elektronen-Synchrotron, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules, H2020 European Research Council
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