Discovery of a low-surface-brightness galaxy in the Zone of Avoidance using VVVX Deepstack imaging

Abstract

We report the discovery of VVVX J080705.96−273823.6, the first low-surface-brightness galaxy candidate identified in the Zone of Avoidance by the VISTA Variables in the Vía Láctea eXtended Survey (VVVX). The source was detected serendipitously during a visual inspection of the new Deepstack images, a set of reconstructed mosaics generated through an updated reprocessing. The associated stacking procedure that significantly improves both the depth and spatial uniformity of the original survey images. First-order morpho-photometric parameters were obtained using SExtractor in combination with PSF models derived with PSFEx, applied to star-subtracted images to minimize foreground contamination. The final structural properties of the galaxy were derived from PSF-convolved modelling of azimuthally averaged surface-brightness profiles in the J, H, and Ks bands using exponential, Sérsic, and composite models. The galaxy candidate is clearly detected in the three available near-infrared bands. The azimuthally averaged profiles are consistently described by a disk-dominated (exponential) model in all three bands, with exponential scale lengths in the range h ∼ 32–36″ and extinction-corrected central surface brightness values spanning μ0 ≃ 19.82–22.35 mag arcsec−2. The J band gives the best-constrained profile; H and Ks show the same behaviour with larger uncertainties. The projected proximity to the galaxies ESO 494−25 and ESO 494−26 raises the possibility of a physical association. Both ESO galaxies have radial velocities consistent with distances of ∼11–12 Mpc. If VVVX J080705.96−273823.6 were located at the same distance, its characteristic exponential scale length of h ≃ 34″ would correspond to ∼1.8–2.0 kpc, consistent with the range of scale lengths observed in nearby LSB disk galaxies. However, in the absence of a spectroscopic redshift, this association remains tentative. This discovery demonstrates that the new VVVX Deepstack products can reveal faint diffuse galaxies at low Galactic latitudes, opening a path toward a more complete census of the obscured nearby Universe.