ZTF SN Ia DR2 follow-up: Characterization of subluminous Type Ia supernovae in the ZTF DR2 full sample
Year: 2026
Type: article
Abstract: The Zwicky Transient Facility Data Release 2 (ZTF DR2) includes a total of 3628 Type Ia supernovae (SNe Ia), providing the largest and most complete sample of spectroscopically confirmed SNe Ia at low redshift to date. In this paper, we present a photometric and spectroscopic analysis of 124 subluminous SNe Ia, the largest sample of spectroscopically classified subluminous Type Ia supernova observed with a single instrument, comprising 87 91bg-like, 12 86G-like, 18 04gs-like, and 7 02es-like events. We complement the published DR2 SALT2 light-curve parameters with new parameters obtained using template-based fits from SNOOPY. We measured the expansion velocities and pseudo-equivalent widths (pEW) of key spectral features using SPEXTRACTOR. Next, the spectral averages were constructed for each subluminous subtype, binned by phase. We also analyzed the host galaxy environments, both global and local, in terms of g − z color, stellar mass, and directional light radius (dDLR). We found that all subluminous SNe Ia (except the 02es-like subtype) are intrinsically red. This is made evident when we separate the extrinsic color components from intrinsic ones. Since SALT2 has not been trained on subluminous SNe Ia, it compensates for their redder colors by inflating the c parameter, thereby extending the luminosity-width relation to negative values of x1. As expected, all subluminous SNe Ia fall within the cool region of the Branch et al. (2006, PASP, 118, 560) diagram, with the exception of 02es-like events, which display lower Si IIλ5972 pEW values. All subluminous subtypes tend to occur in more massive, redder host galaxies and in the reddest local environments within their stellar mass bins. Notably, 91bg- and 86G-like SNe Ia explode at significantly larger normalized galactocentric distances. Finally, we identified the pEW of the blended Ti II+Si II+Mg II absorption feature at 4300 Å, along with sBV, as robust and sufficient indicators for subclassifying subluminous SNe Ia.
Authors: Alaa Alburai, Lluís Galbany, Umut Burgaz, Georgios Dimitriadis, Joel Johansson, Mat Smith, Ramon Sanfeliu, Sandra Guerra, Tomás Müller-Bravo, Ariel Goobar, Suhail Dhawan, Young-Lo Kim, Jakob Nordin, Alice Townsend, Jesper Sollerman, Madeleine Ginolin, Mickael Rigault, Jacco H. Terwel, Roger Smith, Avery Wold, Tracy X. Chen, Theophile Jegou du Laz
Institutions: Institute of Space Sciences, Institut d'Estudis Espacials de Catalunya, Trinity College Dublin, Lancaster University, Stockholm University, Arturo Prat University, University of Birmingham, Humboldt-Universität zu Berlin, Lyon 1 Université, Centre National de la Recherche Scientifique, Institut National de Physique Nucléaire et de Physique des Particules, Institut de Physique des 2 Infinis de Lyon, California Institute of Technology, Infrared Processing and Analysis Center, Yonsei University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Gordon and Betty Moore Foundation, California Institute of Technology, Northwestern University, University of Washington, University of Warwick, European Commission, National Research Foundation, Trinity College Dublin, Weizmann Institute of Science, National Research Foundation of Korea, Knut och Alice Wallenbergs Stiftelse, Vetenskapsrådet, Stockholms Universitet, Universitat Autònoma de Barcelona, HORIZON EUROPE Framework Programme, Deutsches Elektronen-Synchrotron, Agència de Gestió d'Ajuts Universitaris i de Recerca, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules
Awards: Charting new physics with time-domain astronomy, The SED Machine: an Efficient Transient Classifier, G2262748287, G2601397997, Exploring & Exploiting the Dynamic Optical Sky, G288263039, G300979063, G3320050967, G3480869486, ZWICKY TRANSIENT FACILITY, G3681454997, G4042783231, G4212629114, G425668148, G434337789, G4436073038, G4881091899, G5013843854, G5077476177, G5080475149, G5852091828, G617610489, PIRE: GROWTH: Global Relay of Observatories Watching Transients Happen, G6853635150, G7137047011
OpenAlex ID: W7124430603
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