The extremely low-luminosity Type Iax SNe 2022ywf and 2023zgx

¹ Department of Experimental Physics, University of Szeged, Dóm tér 9, H-6720 Szeged, Hungary
² HUN-REN-SZTE Stellar Astrophysics Research Group, Szegedi út, Kt. 766, 6500 Baja, Hungary
³ MTA-ELTE Lendület “Momentum” Milky Way Research Group, Szent Imre H. st. 112, 9700 Szombathely, Hungary
⁴ European Southern Observatory, Alonso de Córdova 3107 Vitacura, Casilla, 19001, Santiago, Chile
⁵ Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854, USA
⁶ Department of Physics and Astronomy, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA
⁷ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA
⁸ Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, 32001 Jhongli, Taiwan
⁹ Las Cumbres Observatory, 6740 Cortona Drive, Suite 102 Goleta, CA 93117-5575, USA
¹⁰ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
¹¹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
¹² Department of Astronomy & Astrophysics, University of California, San Diego, 9500 Gilman Drive, MC 0424 La Jolla, CA 92093-0424, USA
¹³ Cardiff Hub for Astrophysics Research and Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁴ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), 1800 Sherman Ave., Evanston, IL 60201, USA
¹⁵ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
¹⁶ Instituto de Ciencias Exactas y Naturales (ICEN), Universidad Arturo Prat, Iquique, Chile
¹⁷ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400 Austin, TX 78712, USA
¹⁸ Center for Astrophysics and Cosmology, University of Nova Gorica, Vipavska 11c, 5270 Ajdovščina, Slovenia
¹⁹ School of Physics and Astronomy, Monash University, Clayton, Australia
²⁰ OzGrav: The ARC Center of Excellence for Gravitational Wave Discovery, Clayton, Australia
²¹ Astrophysics sub-Department, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
²² Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17 Budapest 1121, Hungary

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Received: 26 November 2025
Accepted: 25 February 2026

Abstract

Context. We present the optical follow-up of SNe 2022ywf and 2023zgx, two examples from the Iax subclass of thermonuclear supernova (SN) events. With peak absolute magnitudes of M_V = −13.7 and −14.4 mag, respectively, both objects belong to the extremely low-luminosity (EL) population of the class.

Aims. The common origin of SNe in the Iax subclass remains under debate, since the distribution of certain observables may indicate that the extremely low-luminosity explosions form a distinct population. We aim to estimate the physical properties of the two EL objects, including mapping the ejecta structure. We compare the results with the predictions of the pure deflagration model with similar luminosity, as well as with the common features of other SNe Iax.

Methods. We performed spectral tomography on the spectral series of SNe 2022ywf and 2023zgx around their maxima to map the physical properties of the ejecta. Together with the analysis of BgVriz photometry, we studied a wide range of observables to investigate their distribution against luminosity. We compared the constrained chemical abundances of the ejecta to the predictions of hydrodynamic simulations with similar peak luminosities.

Results. Constant abundances provide a good match for the distribution of chemical elements for both SNe 2022ywf and 2023zgx. The discrepancies compared to the least luminous pure deflagration model N5def_hybrid are minor, especially at post-maximum epochs. The two SNe also share similar characteristics in their constrained density structures, as well as in the evolution of the photosphere.

Conclusions. The analysis supports the assumption that pure deflagration models can reproduce the main characteristics of SNe Iax, even for the low-luminosity population. The presented indirect observational evidence indicates that these objects show similar intrinsic properties to the well-studied, relatively luminous Iax sample and fit into the velocity distribution of the subclass.