The VVV near-IR galaxy catalogue of the southern Galactic disc

TL;DR

This paper presents a comprehensive near-infrared galaxy catalogue of the southern Galactic disc's Zone of Avoidance, utilizing AI techniques to identify and characterize over 167,000 galaxies, aiding extragalactic research in obscured regions.

Contribution

The study introduces a new large-scale NIR galaxy catalogue covering the southern Galactic disc, employing neural networks and machine learning for galaxy identification in the ZoA.

Findings

Catalogue includes 167,559 galaxies with photometric and morphological data.

AI classifiers achieved 14% confirmation rate through visual or catalogue matching.

Galaxy density influenced by Milky Way extinction, with detectable inhomogeneities indicating structures.

Abstract

The distribution of galaxies in the Zone of Avoidance (ZoA) is incomplete due to the presence of our own Galaxy. Our research focused on the identification and characterisation of galaxies in the ZoA, using the new near-infrared data from the VVVX survey in the regions that cover the southern Galactic disc. We used our previously-established procedure based on photometric and morphological criteria to identify galaxies. The large data volume collected by the VVVX required alternatives to visual inspection, including artificial intelligence techniques, such as classifiers based on neural networks. The VVV NIR galaxy catalogue is presented, covering the southern Galactic disc, significantly extending the vision down to $K^0_s=16$ mag throughout the ZoA. This catalogue provides positions, photometric and morphological parameters for a total of 167,559 galaxies with their probabilities determined by the CNN and XGBoost algorithms based on image and photometric data, respectively. The construction of the catalogue involves the employment of optimal probability criteria. 14% of these galaxies were confirmed by visual inspection or by matching with previous catalogues. The peculiarities exhibited by distinct regions across the Galactic disc, along with the characteristics of the galaxies, are thoroughly examined. The catalogue serves as a valuable resource for extragalactic studies within the ZoA, providing a crucial complement to the forthcoming radio catalogues and future surveys utilizing the Vera C.~Rubin Observatory and the Nancy Grace Roman Space Telescope. We present a deep galaxy map, covering a 1080 sq. deg. region, which reveals that the apparent galaxy density is predominantly influenced by foreground extinction from the Milky Way. However, the presence of intrinsic inhomogeneities, potentially associated with candidate galaxy groups or clusters and filaments, is also discernible.