An Overview of Optical Galaxy Searches and their Completeness

Abstract

Dust and stars in the Milky Way create a ``Zone of Avoidance'' (ZOA) in the distribution of optically visible galaxies of about 25% of the sky. To reduce this gap, optical searches for partially obscured galaxies have been performed. The status of these deep searches, in particular their completeness as a function of foreground extinction are discussed. Using existing sky surveys, over 50000 previously unknown galaxies have been identified. The surveys cover practically the whole ZOA. It is shown that these surveys are complete for galaxies with extinction-corrected diameters D^o ge 1.3 arcmin to extinction levels of A_B le 3.0 mag. Incorporating these new data in a whole-sky map of galaxies complete to D^o ge 1.3 arcmin finds the ZOA reduced by a factor of about 2 to 2.5, respectively from extinction levels of A_B = 1.0 mag to A_B = 3.0 mag (see Fig.~4).