JWST nebular spectroscopy of SN 2023qov: Circumstellar dust emission in a normal type Ia supernova

Abstract

We present panchromatic observations of the Type Ia supernova (SN Ia) 2023qov, ranging from ~2 weeks before to ~1 yr after maximum light. JWST near- and mid-infrared spectra at +276 and +363 days show ~400 K dust emission that cools by ~75 K between epochs, the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. We find that the emission is well described by models of carbonaceous dust placed within ~1 lt-yr of the SN, with a dust mass of ~10-4 M⊙. We do not see evidence of active dust creation, suggesting an infrared light echo by preexisting circumstellar dust as the likely source of the emission. The JWST nebular line profiles suggest asymmetric, stratified ejecta, similar to other normal SNe Ia, though a slight double-horn structure in the argon lines indicates a toroidal enhancement. SN 2023qov exhibits a slightly red, fast-declining early light curve (∆m15(B) = 1.47 ± 0.05 mag), from which we determine a 56Ni mass of M56 = 0.21 ± 0.04 M⊙, and a distance of d = 36.0 ± 1.8 Mpc to the SN and its host, NGC 7029. The presence of circumstellar dust around a normal SN Ia has implications both for the progenitor system, suggesting a less than pristine environment, and for cosmology, as a possible source of reddening and extinction that can affect distance inferences.