A SIMPLE EFFECTIVE METHOD TO ESTIMATE THE GALACTIC EXTINCTION TOWARDSGALAXIES IN THE PLANE OF THE MILKY-WAY

Elliptical galaxies and bulges of spiral galaxies have quite similar, well-defined optical colours. It is just these bulges that are left if a (spiral) galaxy suffers from a considerable foreground extinction a s is the case for many of the thousands of galaxies that have been det ected in recent years in the ''zone-of-avoidance'' of the Milky Way. B y use of the ''old'' Palomar Sky Survey (whose red-sensitive and blue- sensitive exposures had consecutively been taken for each field), meas uring the red and blue bulge profiles there, led to astonishingly accu rate results for their galactic, i.e. foreground extinction. With this quick and simple method it will be possible in future to determine th e total galactic extinction along many lines-of-sight in the Galaxy, t o supplement data on the spatial distribution of the interstellar exti nction with a maximum value and, eventually, to develop a dust-model o f the Milky Way. We detected a pronounced dependence of the 100 mu m v s A(V) or 60 mu m vs A(V) ratio on the galactic longitude.