SIMBAD references

Narrowband-filter imaging spectrophotometry is a powerful tool for studying the spatial behavior of physical parameters, such as interstellar reddening, excitation, electron temperature, and densities or chemical abundances across extended objects such as nebulae and galaxies. We explore the hazards and technical limits of the method of spectral imaging with narrowband interference filters. We discuss the specific application of statistical errors involved in the estimation of abundance gradients from nebular line flux measurements and the impact of those errors on interpretation. We demonstrate that a sample of at least 16 H II regions is needed for a meaningful and robust description of radial abundance gradients in disk galaxies. We also discuss the systematic errors introduced by the uncertainty related to the subtraction of the underlying stellar continuum from monochromatic emission-line images; we demonstrate that the quality of subtraction of the underlying continuum is the main limit on the precision of imaging spectrophotometry with narrowband filters. Finally, we investigate the impact of selection effects on the derivation of physical parameters from measurements involving the ratio of two or more spectral lines.