The Extremely Metal-Poor SN 2023ufx: A Local Analog to High-Redshift Type II Supernovae

Abstract

We present extensive observations of the Type II supernova (SN II) 2023ufx which is likely the most metal-poor SN II observed to-date. It exploded in the outskirts of a low-metallicity ($Z_{\mathrm{host}}\sim 0.1Z_{\odot }$) dwarf ($M_g=-13.23\pm 0.15$~mag; $r_e\sim 1$~kpc) galaxy. The explosion is luminous, peaking at $M_g\approx -18.5$mag, and shows rapid evolution. The $r$-band (pseudo-bolometric) light curve has a shock-cooling phase lasting 20 (17) days followed by a 19 (23)-day plateau. The entire optically-thick phase lasts only $\approx 55$days following explosion, indicating that the red supergiant progenitor had a thinned H envelope prior to explosion. The early spectra obtained during the shock-cooling phase show no evidence for narrow emission features and limit the pre-explosion mass-loss rate to $\dot{M}\lesssim 10^{-3}{\mathrm{M}}_{\odot }$/yr. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of $\lesssim 0.1Z_{\odot }$. The semi-nebular ($\sim 60-130$d) spectra reveal weak Fe II, but other metal species typically observed at these phases (Ti II, Sc II, Ba II) are conspicuously absent. The late-phase optical and near-infrared spectra also reveal broad ($\approx 10^4\mathrm{km}{\mathrm{s}}^{-1}$) double-peaked H$\hat{I}\pm$, P${\hat{I}}^2$, and P${\hat{I}}^3$ emission profiles suggestive of a fast outflow launched during the explosion. Outflows are typically attributed to rapidly-rotating progenitors which also prefer metal-poor environments. This is only the second SN II with $\lesssim 0.1Z_{\odot }$ and both exhibit peculiar evolution, suggesting a sizable fraction of metal-poor SNe II have distinct properties compared to nearby metal-enriched SNe II. These observations lay the groundwork for modeling the metal-poor SNe II expected in the early Universe.

17 pages, 15 figures and 3 tables in main text, an additional 5 pages, 4 figures, and 2 tables in the appendix. Accepted by ApJ, spectra and photometry are included as ancillary data