Spitzer IRAC Observations of Newly Discovered Planetary Nebulae from the Macquarie-AAO-Strasbourg Hα Planetary Nebula Project

We compare Hα, radio continuum, and Spitzer Space Telescope images of 58 planetary nebulae (PNe) recently discovered by the Macquarie-AAO-Strasbourg Hα PN Project (MASH) of the SuperCOSMOS Hα Survey. Using Infrared Array Camera (IRAC) data, we examine the relationships between optical and MIR morphologies from 3.6 to 8.0 μm and explore the ratio of mid-infrared (MIR) to radio nebular fluxes, which is a valuable discriminant between thermal and nonthermal emission. MASH emphasizes late evolutionary stages of PNe compared with previous catalogs, enabling study of the changes in MIR and radio flux that attend the aging process. Spatially integrated fluxes are constructed for all MASH PNe observed by the GLIMPSE Legacy Project, using the Hα morphologies to define the areas of MIR and radio continuum emission observed by the Midcourse Space Experiment (MSX), IRAC, the Molonglo Observatory Synthesis Telescope, and the Very Large Array (VLA). The ratio of IRAC 8.0 μm to MSX 8.3 μm fluxes provides an assessment of the absolute diffuse calibration of IRAC at 8.0 μm. We independently confirm the aperture correction factor to be applied to IRAC at 8.0 μm to align it with the diffuse calibration of MSX. The result is in accord with the recommendations of the Spitzer Science Center and with our results from a parallel study of H II regions in the MIR and radio. However, these PNe probe the diffuse calibration of IRAC on a spatial scale of 9^''-77^'', as opposed to the many-arcminute scale from the H II regions' study.