INFRARED SPECTRAL MAPPING OF SUPERNOVA REMNANTS. I. N63A AND ITS ENVIRONMENT

We present Spitzer Space Telescope spectra of the supernova remnant (SNR) N63A and its native H II region N63 in the Large Magellanic Cloud. We measure nebular fine-structure lines, H2 lines, and polycyclic aromatic hydrocarbons (PAHs). The lines contribute half of the flux in the Spitzer 24 μm image of N63A shocked lobes, but only ≤10% elsewhere. The mid-IR flux is largely due to thermal continuum emission from dust in and around N63A plasma. Electron densities are low everywhere; the differences in mid-IR line ratios separate N63A plasma and its high-excitation surroundings from N63A low-excitation optical lobes. We compare the observed line fluxes and ratios within N63A's shocked lobes and plasma with the predictions from models for moderate and fast shocks to constrain pre-shock densities and shock velocities. N63A's photoionized lobe contains a warm photodissociation region in pressure equilibrium with optically ionized gas. We apply a physical dust model to our spectra supplemented by MIPS photometry. We derive the intensity of radiation heating the dust, the mass fraction due to PAHs, and the masses of dust within our sampled regions and of cooler grains in the diffuse interstellar medium. N63A's shocked lobes and plasma contain ∼0.07 M☉ of hot grains, comparable to amounts in other SNRs. Within N63A there is ∼0.7 M☉ of warm grains exposed to ≥100 times the intensity of the local interstellar radiation field. Within the regions, 92% of the total dust mass resides in cool grains emitting ≤27% of their mid-IR luminosity.