DISCOVERY OF HIGHLY OBSCURED GALAXIES IN THE ZONE OF AVOIDANCE

Abstract

We report the discovery of 25 previously unknown galaxies in the zone of avoidance (ZoA). Our systematic search for extended extragalactic sources in the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and MIPS Galactic Plane Survey (MIPSGAL) mid-infrared surveys of the Galactic plane has revealed two overdensities of these sources, located around l ~ 47° and 55° and |b| ≾ 1° in the Sagitta-Aquila region. These overdensities are consistent with the local large-scale structure found at similar Galactic longitude and extending from |b| ~ 4 to 40°. We show that the infrared spectral energy distribution of these sources is indeed consistent with those of normal galaxies. Photometric estimates of their redshift indicate that the majority of these galaxies are found in the redshift range z ≃ 0.01-0.05, with one source located at z ≃ 0.07. Comparison with known sources in the local universe reveals that these galaxies are located at similar overdensities in redshift space. These new galaxies are the first evidence of a bridge linking the large-scale structure between both sides of the Galactic plane at very low Galactic latitude and clearly demonstrate the feasibility of detecting galaxies in the ZoA using mid-to-far infrared surveys.