The Extremely Metal-Poor SN 2023ufx: A Local Analog to High-Redshift Type II Supernovae
arxiv(2024)
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_ 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.
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