PSF-fitting techniques for crowded field 3D spectroscopy


Martin M. Roth


In retrospect, it was the advent of the CCD as a linear, high dynamic range panoramic detector which made it possible to overcome the source confusion problem for stellar photometry, e.g. in star clusters, local group galaxies, etc. The ability of accurately sampling the point-spread-function (PSF) in two dimensions and to use it as a template for fitting severely overlapping stellar images is of fundamental importance for crowded-field photometry, and has thus become the foundation for the determination of accurate CMDs of globular clusters and the study of resolved stellar populations in nearby galaxies. Analogous to CCDs, the introduction of integral field spectrographs has opened a new avenue for crowded-field 3D spectroscopy, which benefits in the same way from PSF-fitting techniques as does CCD photometry. I shall present our experience with sampling the PSF with 3D spectroscopy, review the effects of atmospheric refraction, discuss background subtraction problems, and present several science applications as obtained from observations with the PMAS and VIMOS instruments. I shall conclude with an outlook into science cases with AO-assisted 3D spectroscopy and future prospects of Extremely Large Telescopes.