How do supernova remnants cool? – I. Morphology, optical emission lines, and shocks

Abstract

Supernovae (SNe) inject ∼1051 erg in the interstellar medium, thereby shocking and heating the gas. A substantial fraction of this energy is later lost via radiative cooling. We present a post-processing module for the flash code to calculate the cooling radiation from shock-heated gas using collisional excitation data from mappings v. When applying this tool to a simulated SN remnant (SNR), we find that most energy is emitted in the EUV. However, optical emission lines ([O III], [N II], [S II], Hα, Hβ) are usually best observable. Our shock detection scheme shows that [S II] and [N II] emissions arise from the thin shell surrounding the SNR, while [O III], H$\rm \alpha$, and H$\rm \beta$ originate from the volume-filling hot gas inside the SNR bubble. We find that the optical emission lines are affected by the SNR’s complex structure and its projection onto the plane of the sky because the escaping line luminosity can be reduced by 10 – 80% due to absorption along the line-of-sight. Additionally, the subtraction of contaminating background radiation is required for the correct classification of an SNR on the oxygen or sulphur BPT diagrams. The electron temperature and density obtained from our synthetic observations match well with the simulation but are very sensitive to the assumed metallicity.

Cloud Formation by Supernova Implosion

“…In a more realistic description of the ISM, the ambient medium is highly structured due to the combined effect of turbulence, shear, and stratification. SNe exploding in such an environment will follow the geometry of the ISM (Makarenko et al 2023), as the shock wave can only slowly penetrate into dense structures, but it will quickly fill out the volume-filling low-density medium, leading to highly amorphous SNR shapes (Kim & Ostriker 2015;Lancaster et al 2021). In such a configuration, the SNR will reach pressure equilibrium at different times in different directions, leading to a displacement and deformation of the clouds formed in this way.…”

“…SNR evolution in a uniform medium has been studied at great length using analytical models (e.g., Woltjer 1972;Gaffet 1978;Ostriker & McKee 1988), as well as numerical simulations in one (e.g., Chevalier 1974;Cioffi et al 1988;Fierlinger et al 2016), two (e.g., Blondin et al 1998;Ntormousi et al 2011;Meyer et al 2023), and three dimensions (e.g., Kim & Ostriker 2015;Makarenko et al 2023), which have lead to a comprehensive picture comprised of a series of different stages, characterized by different deceleration parameters q = −d 2 R/ dt 2 and conserved quantities. In the first stage, known as the free expansion phase, the SNR expands with constant velocity until the reverse shock has fully thermalized the ejecta (Truelove & McKee 1999).…”

Detection of Metal Enrichment by SN 2011jm in NGC 4809

“…These collisionally excited lines, such as the [N II] λ6583/Hα and [S II]λ6731/Hα line ratios, are crucial for classifying an object as an SN remnant (SNR). Makarenko et al (2023) proposed a criterion requiring [N II]λ6583/ Hα > 0.5 and [S II]λ6731/Hα > 0.4 to identify SNRs. However, at the pixel of SN 2011jm site, we compute the ratios of [N II]λ6583/Hα = 0.12 ± 0.02 and [S II]λ6731/Hα = 0.06 ± 0.01, significantly below the specified criterion.…”