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@ARTICLE{Ginolin:644482,
      author       = {Ginolin, M. and Rigault, M. and Copin, Y. and Ruppin, F.
                      and Dimitriadis, G. and Goobar, A. and Johansson, J. and
                      Maguire, K. and Nordin, J. and Amenouche, M. and Aubert, M.
                      and Barjou-Delayre, C. and Betoule, M. and Burgaz, U. and
                      Carreres, B. and Deckers, M. and Dhawan, S. and Feinstein,
                      F. and Fouchez, D. and Galbany, L. and Ganot, C. and de
                      Jaeger, T. and Kenworthy, W. D. and Kowalski, M. and
                      Muller-Bravo, T. E. and Nugent, P. and Racine, B. and
                      Rosnet, P. and Rosselli, D. and Sollerman, J. and Terwel, J.
                      H. and Townsend, A. and Bellm, E. C. and Kasliwal, M. M. and
                      Laher, R. R. and Masci, F. J. and Riddle, R. L.},
      title        = {{ZTF} {SN} {I}a {DR}2: {E}nvironmental dependencies of
                      stretch and luminosity for a volume-limited sample of 1000
                      type {I}a supernovae},
      journal      = {Astronomy and astrophysics},
      volume       = {695},
      issn         = {0004-6361},
      address      = {Les Ulis},
      publisher    = {EDP Sciences},
      reportid     = {PUBDB-2026-00353, arXiv:2405.20965},
      pages        = {A140},
      year         = {2025},
      note         = {14 pages, 11 figures, accepted by Astronomy and
                      Astrophysics},
      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
                      9.2σ significance. We demonstrate, at the 13.4σ 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
                      $Δα$ = −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 ≥5σ 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.Key words: supernovae: general /
                      dark energy},
      cin          = {$Z_NA$},
      ddc          = {520},
      cid          = {$I:(DE-H253)Z_NA-20210408$},
      pnm          = {613 - Matter and Radiation from the Universe (POF4-613)},
      pid          = {G:(DE-HGF)POF4-613},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)16},
      eprint       = {2405.20965},
      howpublished = {arXiv:2405.20965},
      archivePrefix = {arXiv},
      SLACcitation = {$\%\%CITATION$ = $arXiv:2405.20965;\%\%$},
      doi          = {10.1051/0004-6361/202450378},
      url          = {https://bib-pubdb1.desy.de/record/644482},
}