Enlightening the Universe behind the Milky Way bulge: II. Morphological classification and galaxy properties

Abstract

Context. The detection of extragalactic sources beyond the Milky Way is limited by the location of the Solar system. In the zone ofavoidance (ZOA), optical observations are hindered by stellar crowding and Galactic absorption. To fully understand the backgroundgalaxy population in this region, observations at longer wavelengths are needed.Aims. The objective of this study is to determine the characteristics of galaxies that are situated behind the Milky Way bulge throughthe use of near-infrared (NIR) data obtained from the VISTA Variables in Vía Láctea (VVV) survey.Methods. The galaxy candidates were visually confirmed, and a morphological classification of all sources was performed based ontheir appearance, by differentiating between elliptical, spiral, undefined, and doubtful galaxies. Additionally, the surrounding area wasclassified based on the number of sources that are detected in the same target field. Isolated galaxies, galaxies with close companions,and galaxies in denser environments were catalogued.Results. Following a visual inspection, 14480 galaxy candidates were classified morphologically: 3702 as elliptical, 1704 as spiral,6425 as undefined, and 2649 as doubtful. The environmental classification showed that 73.9% were isolated, 12.4% had close companions, and 13.7% were in denser environments. Our catalogue shows slower proper motions than star catalogues. The majorityof galaxies that are classified as elliptical and spiral manifest SExtractor parameters that are indicative of this category of sources.Additionally, elliptical galaxies in denser environments appear to be redder than spiral galaxies in isolated environments.Conclusions. A total of 14480 galaxy candidates were subjected to a morphological classification in the region of the Milky Waybulge. This result verifies the efficacy of the VVV/VVVX survey in identifying and characterising a diverse range of galaxies andextragalactic structures that are obscured by the Milky Way. The survey thereby contributes to a more profound understanding of theUniverse in the ZOA.