Spitzer Spectroscopy of the Galactic Supernova Remnant G292.0+1.8: Structure and Composition of the Oxygen-Rich Ejecta

Abstract

We present mid-infrared (5-40 micron) spectra of shocked ejecta in the Galactic oxygen-rich supernova remnant G292.0+1.8, acquired with the IRS spectrograph on board the Spitzer Space Telescope. The observations targeted two positions within the brightest oxygen-rich feature in G292.0+1.8. Emission lines of [Ne II] 12.8, [Ne III] 15.5, 36.0, [Ne V] 24.3 and [O IV] 25.9 are detected from the shocked ejecta. No discernible mid-IR emission from heavier species such as Mg, Si, S, Ar or Fe is detected in G292.0+1.8. We also detect a broad emission bump between 15 and 28 microns in spectra of the radiatively shocked O-rich ejecta in G292.0+1.8. We suggest that this feature arises from either shock-heated Mg2SiO4 (forsterite) dust in the radiatively shocked O-rich ejecta, or collisional excitation of PAHs in the blast wave of the SNR. If the former interpretation is correct, this would be the first mid-IR detection of ejecta dust in G292.0+1.8. A featureless dust continuum is also detected from non-radiative shocks in the circumstellar medium around G292.0+1.8. The mid-IR continuum from these structures is well described by a two-component dust model. The temperature of the hot dust component (mass ~ 0.002 Solar masses) is ~ 115 K, while that of the cold component (> = 3 Solar masses) is ~ 35 K. We attribute the hot component to collisionally heated dust in the circumstellar shocks in G292.0+1.8, and attribute the cold component to dust heated by the hard FUV radiation from the circumstellar shocks. Our models yield mid-IR line strengths consistent with M(O)/M(Ne) ~ 3, M(O)/M(Si) >~ 61 and M(O)/M(S) ~ 50. These ratios are difficult to reproduce with standard nucleosynthesis models of well-mixed SN ejecta (abridged).

ApJ, in press; 16 pages, 3 tables, 6 figures

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• Spitzer Imaging and Spectral Mapping of the Oxygen-Rich Supernova Remnant G292.0+1.8
• AKARI Infrared Observations of the Supernova Remnant G292.0+1.8: Unveiling Circumstellar Medium and Supernova Ejecta
• SOFIA/FORCAST Galactic Center Legacy Survey: Overview
• X-ray ejecta kinematics of the Galactic core-collapse supernova remnant G292.0+1.8
• Spitzer IRS Observations of the XA Region in the Cygnus Loop Supernova Remnant
• IRAS 15099-5856: Remarkable Mid-Infrared Source with Prominent Crystalline Silicate Emission Embedded in the Supernova Remnant MSH15-52
• The Cold Dust Content of the Oxygen-Rich Supernova Remnant G292.0+1.8
• High Spatial Resolution Spectroscopy of G292.0+1.8 with Chandra
• VLT/X-shooter Spectroscopy of a Dusty Planetary Nebula Discovered with Spitzer/IRS
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