III. Automatic extraction for millions of galaxies
G. Paturel, Yuhong Fang, C. Petit, Robert Garnier, Judith Rousseau · 2000
This paper presents a method for extracting a catalogue of galaxy candidates from the Digitized Sky Survey (DSS). The method is based on a functional anal- ysis applied on each individual plate. The standard devia- tion of pixel optical densities versus the inverse of surface area leads to a diagram in which extended and star-like objects are well separated. This diagram is used for a pre- liminary recognition. Then, a ltering process is applied using a Neural Network method associated with a training sample built with well identied objects. The main cata- logue gives coordinates, total magnitude, isophotal diam- eter, axis ratio, position angle for 2 772 061 galaxy candi- dates. The method favors the detection of normal galaxies. This creates a bias against compact high surface bright- ness galaxies.