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

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_ host∼ 0.1 Z_⊙) dwarf (M_g = -13.23±0.15 mag; r_e∼ 1 kpc) galaxy. The explosion is luminous, peaking at M_g≈ -18.5mag, 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 ≈ 55days 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 Ṁ≲ 10^-3  M_⊙/yr. The photospheric-phase spectra are devoid of prominent metal absorption features, indicating a progenitor metallicity of ≲ 0.1 Z_⊙. The semi-nebular (∼ 60-130d) 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 (≈ 10^4 km  s^-1) double-peaked Hα, Pβ, and Pγ 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 ≲ 0.1 Z_⊙ 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.