Characterizing the outer disk of extended-UV galaxies in the optical domain with deep surveys

¹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
² Instituto de Astrofísica de Canarias, Vía Láctea S/N, E-38205 La Laguna, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Spain
⁴ National Centre for Nuclear Research, Pasteura 7, 02-093 Warsaw, Poland
⁵ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile

^⋆ Corresponding author: eloise.bernaud@lam.fr

Received: 23 April 2025
Accepted: 11 June 2025

Abstract

Aims. Extended-UV (XUV) galaxies are galaxies that present an extended outer ultraviolet disk. Although some giant low surface brightness (GLSB) galaxies are also XUV, their relation has been seldom studied. This work aims to determine whether a sample of nine XUV galaxies can be classified as GLSB galaxies, by analyzing their photometric properties in deep optical images.

Methods. The method presented here used optical data from the Dark Energy Survey to construct surface brightness profiles for each galaxy. We defined a characteristic UV radius to examine the XUV disks. We fitted the surface brightness profiles using simple exponential functions, and compared the extracted parameters with the literature to identify possible GLSB galaxies. We also examined other diagnostics, including color profiles.

Results. The analysis of the optical surface brightness profiles of XUV galaxies reveals that they can be classified into three different families. One third meet the GLSB criteria in terms of diffuseness, another third are regular, and the remaining have a stronger decline in the outer disk than in the inner disk, which is opposite to the characteristics of GLSB galaxies. The color profile allowed us to distinguish one galaxy, NGC1140, and speculate that it is the result of a rare dwarf-dwarf merger.