ZTF SN Ia DR2: The diversity and relative rates of the thermonuclear supernova population

¹ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
² Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
³ Oskar Klein Centre, Department of Physics, Stockholm University, SE-10691 Stockholm, Sweden
⁴ Université Claude Bernard Lyon 1, CNRS, IP2I Lyon / IN2P3, IMR 5822, F-69622 Villeurbanne, France
⁵ Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁶ Oskar Klein Centre, Department of Astronomy, Stockholm University, SE-10691 Stockholm, Sweden
⁷ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
⁸ Institut d’Estudis Espacials de Catalunya (IEEC), E-08034 Barcelona, Spain
⁹ Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208, USA
¹⁰ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Ave, Evanston, IL 60201, USA
¹¹ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50B-4206, Berkeley, CA 94720, USA
¹² Department of Astronomy, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
¹³ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl St, 7610001 Rehovot, Israel
¹⁴ Institute of Astronomy and Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁵ IPAC, California Institute of Technology, 1200 E. California Blvd, Pasadena CA 91125, USA
¹⁶ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
¹⁷ Department of Astronomy, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
¹⁸ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
¹⁹ Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, ES-38711 Breña Baja, Spain

^⋆ Corresponding author; g.dimitriadis@lancaster.ac.uk

Received: 9 August 2024
Accepted: 4 December 2024

Abstract

The Zwicky Transient Facility SN Ia Data Release 2 (ZTF SN Ia DR2) contains more than 3000 Type Ia supernovae (SNe Ia), providing the largest homogeneous low-redshift sample of SNe Ia. Having at least one spectrum per event, this data collection is ideal for large-scale statistical studies of the photometric, spectroscopic and host-galaxy properties of SNe Ia, particularly of the rarer ‘peculiar’ sub-classes. In this paper we first present the method we developed to spectroscopically classify the SNe in the sample, and the techniques we used to model their multi-band light curves and explore their photometric properties. We then show a method to distinguish between the peculiar sub-types and the normal SNe Ia. We also explore the properties of their host galaxies and estimate their relative rates, focusing on the peculiar sub-types and their connection to the cosmologically useful SNe Ia. Finally, we discuss the implications of our study with respect to the progenitor systems of the peculiar SN Ia events.