ZTF SN Ia DR2: Simulations and volume-limited sample

¹ National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
² Université Clermont Auvergne, CNRS/IN2P3, LPCA, F-63000 Clermont-Ferrand, France
³ Univ. Lyon, Univ. Claude Bernard Lyon 1, CNRS, IP2I Lyon/IN2P3, UMR 5822, F-69622 Villeurbanne, France
⁴ Department of Physics, Lancaster University, Lancaster LA14YW, UK
⁵ School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland
⁶ Aix Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
⁷ Department of Physics, Duke University Durham, NC 27708, USA
⁸ Institute of Space Sciences (ICE-CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
⁹ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels (Barcelona), Spain
¹⁰ The Oskar Klein Centre, Department of Physics, AlbaNova, Stockholm University, SE-106 91 Stockholm, Sweden
¹¹ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
¹² The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm, Sweden
¹³ Lawrence Berkeley National Laboratory, 1 Cyclotron Road MS 50B-4206, Berkeley, CA 94720, USA
¹⁴ Department of Astronomy, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
¹⁵ LPNHE, CNRS/IN2P3, Sorbonne Université, Université Paris-Cité, Laboratoire de Physique Nucléaire et de Hautes Énergies, 75005 Paris, France
¹⁶ Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena CA 91125, USA
¹⁷ IPAC, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
¹⁸ Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA

^⋆ Corresponding authors; melissa.amenouche@nrc-cnrc.gc.ca , philippe.rosnet@clermont.in2p3.fr, mat.smith@lancaster.ac.uk

Received: 5 September 2024
Accepted: 12 January 2025

Abstract

Type Ia supernovae (SNe Ia) constitute a historical probe for deriving cosmological parameters through the fit of the Hubble-Lemaître diagram, that is, the SN Ia distance modulus versus their redshift. In the era of precision cosmology, realistic simulation of SNe Ia for any survey entering an Hubble-Lemaître diagram is a key tool for addressing observational systematics, such as the Malmquist bias. As the distance modulus of SNe Ia is derived from the fit of their light curves, a robust simulation framework is required. In this paper, we present the performances of the simulation framework skysurvey with the aim to reproduce the Zwicky Transient Facility (ZTF) SN Ia DR2, which covers the first phase of the ZTF and ran from March 2018 to December 2020. The ZTF SN Ia DR2 sample corresponds to almost 3000 classified SNe Ia of cosmological quality. We simulated individual light curves of the ZTF SN Ia DR2 sample to confirm the validity of the framework while taking the observing conditions and instrument performances into account. After the ZTF SN Ia DR2 selection criteria were applied, we found that the simulated fluxes and associated uncertainties agre well with the measured uncertainties when the sky-noise deduced from the observed science magnitude limits is corrected for by a factor 1.23 for the g band, 1.17 for the r band, and 1.20 for the i band. In addition, we accounted for an error floor of 2.5%, 3.5%, and 6% of the flux level in the g, r, and i bands, respectively. Furthermore a redshift dependence of the SALT2 light-curve parameters (stretch and colour) was conducted to deduce the redshift limit that defines a volume-limited sample, that is, an unbiased SNe Ia sample. We found that the ZTF SN Ia DR2 volume-limited sample is characterized by z ≤ 0.06. This volume-limited sample of about 1000 SNe Ia is unique, and an astrophysical analysis can be carried out based on it, or the standardisation procedure can be tested with unprecedented precision (these analyses are presented in companion papers).