The Nature of the Young Supernova Remnant S8 in the Dwarf Galaxy IC 1613

Abstract

Abstract We present subarcsecond optical images and low- to moderate-resolution spectra of the compact, X-ray, and optically bright supernova remnant known as S8 in the nearby dwarf galaxy IC 1613. Deep Hα images of the remnant show a sharply defined crescent-shaped nebula, while narrow passband images reveal a coincident and unexpectedly bright continuum nebulosity exhibiting a size and morphology like that seen for the remnant’s line emissions. Low-dispersion spectra covering 3600–9000 Å show numerous low-ionization line emissions such as [O i] and [Fe ii], along with higher-ionization emission lines including He ii and optical coronal lines [Fe vii], [Fe x], [Fe xi], and [Fe xiv]. This suggests the presence of a wide range of shock velocities from ∼50 to over 350 km s−1, corresponding to preshock densities of ∼1–30 cm−3. Higher-resolution spectra indicate an expansion velocity around 180 km s−1 with an ∼45 km s−1 wide central cavity. The Hα emission spans rest-frame velocities of +120 to −240 km s−1, and we estimate a total nebula mass of 119 ± 34 M ⊙. We conclude that S8 is a relatively young supernova remnant (≃2700–4400 yr) exhibiting properties remarkably like those seen in the young LMC remnant N49, including age, physical size, shock velocities, filament densities, optical line strengths, X-ray and optical luminosities, and coronal line and continuum emissions.