Crowded field 3D spectrophotometry of extragalactic planetary nebulae

The spectrophotometry of extragalactic planetary nebulae in high surface brightness regions of nearby galaxies is notoriously difficult because of the problem of accurately subtracting the local background of unresolved stars and gaseous emission of the ISM. Conventional slit spectroscopy is not very well suited for providing a good estimate of the two-dimensional surface brightness distribution in the continuum, absorption lines, and superimposed emission lines front all of these background sources. The emergent technique of integral field (3D) spectroscopy holds the promise to overcome these limitations, similar to the advance of CCD photometry vs. photoelectric aperture photometry. We discuss basic properties of 3D spectrophotometry, results from a pilot study with planetary nebulae in the bulge of M31, and some more recent results from observations in other local group galaxies.