The Zone of Avoidance: Optical Compared to Near-Infrared Searches

Galaxies uncovered in the Zone of Avoidance (ZOA) with deep optical searches are compared to the distribution of objects in the 2MASS Extended Source Catalog (2MASX). While the galaxy density of optical surveys is strongly correlated to the dust content, and become ineffective in uncovering the galaxy distribution at A_B > 3.0 mag, this effect is much less severe in the NIR. Galaxies can be identified in 2MASS at optical extinction layers of over 10mag. However, star density has been found to be the dominant limiting factor in the NIR in the wider Galactic Bulge region (see Fig. 4) where optical surveys still do quite well. Systematic positional offsets have also been found between objects in the 2MASX and the optical ZOA as well as other galaxy catalogs. These seem to have their origin in the astrometric reference frame used by these surveys as well as different fitting algorithms when determining positions (details are given in the Appendix). The astrometric offsets between 2MASX and more recent galaxy catalogs (or on the Digitized Sky Survey remeasured positions) are of the order of 1 - 1.5 arcsec, comparable to the relative dispersion in positions between these surveys. Still, it is advisable to take this effect into account when combining galaxies from different catalogs for observational purposes.