MIPSGAL 24 {\mu}m Observations of Galactic Planetary Nebulae

TL;DR

This study presents 24 μm imaging and flux measurements for 224 Galactic planetary nebulae, revealing insights into their morphology, dust composition, and emission mechanisms, and comparing these with shorter wavelength data to understand their infrared properties.

Contribution

First comprehensive 24 μm imaging survey of Galactic planetary nebulae, analyzing morphology, fluxes, and IR colors, and comparing with previous studies to refine flux estimates and interpret emission mechanisms.

Findings

Most PNe with extended 24 μm emission are circular, indicating cool grains in AGB mass-loss regions.

Surface brightness profiles suggest constant mass-loss rates in progenitors.

IRAC-MIPSGAL colors indicate diverse emission mechanisms including PAHs, dust, and ionic lines.

Abstract

We have obtained 24 {\mu}m imaging, profiles and fluxes for 224 planetary nebulae (PNe) lying within the limits of the Spitzer MIPSGAL survey. It is noted that most of the PNe having extended 24 {\mu}m emission also possess circular morphologies, suggesting that the emission derives from cool grains located within the AGB mass-loss regimes. Certain of these halos are found to have a surface brightness fall-off which may be consistent with secularly invariant mass-loss within the PNe progenitors. By contrast, the 8.0 {\mu}m envelopes are detected out to smaller distances from the nuclei, and have a steeper rate of surface brightness fall-off; a phenomenon which may arise from changes in the excitation of polycyclic aromatic hydrocarbons (PAHs) within external photo-dissociation regimes (PDRs). Our 24{\mu}m fluxes are compared to those in previously published studies, and this appears to indicate that many of the prior fluxes have been underestimated; a disparity may imply that previous aperture sizes were too small. We have also combined our 24 {\mu}m fluxes with measures at shorter mid-infrared (MIR) wavelengths, taken with the Infrared Array Camera (IRAC). These are used to investigate the positioning of PNe within the IRAC-MIPSGAL colour planes. The [8.0]-[24] and [5.8]-[24] colours are found to be large, and extend over the respective ranges 3.4-8.7 mag, and 5.4-10.3 mag; indices which are only explainable where a broad range of mechanisms contribute to the fluxes, including PAH bands, cool dust continua, and a variety of ionic transitions. These and other components also affect the morphologies of the sources, and lead to wavelength dependent changes in the widths of the profiles.