Astron. Astrophys. Suppl. Ser. 146, 19-29

An image database

III. Automatic extraction for millions of galaxies

G. Paturel - Y. Fang - C. Petit - R. Garnier - J. Rousseau

Send offprint request: G. Paturel

CRAL-Observatoire de Lyon, F-69561 Saint-Genis Laval Cedex, France

Received February 17; accepted June 16, 2000

Abstract:

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 analysis applied on each individual plate. The standard deviation 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 preliminary recognition. Then, a filtering process is applied using a Neural Network method associated with a training sample built with well identified objects. The main catalogue gives coordinates, total magnitude, isophotal diameter, axis ratio, position angle for $2\ 772\ 061$ galaxy candidates. The method favors the detection of normal galaxies. This creates a bias against compact high surface brightness galaxies.

Key words: galaxies -- catalogues -- data analysis