Revisiting the structure of galactic disks with deep imaging^★

¹ Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011 Valladolid, Spain
² Laboratory for Disruptive Interdisciplinary Science (LaDIS), Universidad de Valladolid, 47011 Valladolid, Spain
³ Instituto de Astrofísica e Ciéncia do Espaço, Universidad de Lisboa, OAL, Tapada de Ajuda, PT1349-018 Lisbon, Portugal
⁴ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, E38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain

^★★ Corresponding authors: samaneraji@gmail.com; samane.raji@uva.es

Received: 18 July 2025
Accepted: 24 October 2025

Abstract

Thanks to new advances in astronomical imaging, we can now routinely explore disk galaxy profiles about two magnitudes deeper than the data available 20 years ago. In this regard, it is an opportune time to reevaluate the past classifications of different surface brightness types. In this paper we explore the stellar mass profiles of a sample of disk galaxies with similar stellar masses (∼10¹⁰ M_⊙) using IAC Stripe82 Legacy Project data. We find that Type I, II-CT, and III-d galaxies exhibit edges at surface brightnesses, μ_g(R_edge), of ∼26.5 mag/arcsec² and surface mass densities, Σ(R_edge), of ∼0.5–1 M_⊙/pc². These surface brightnesses had been outside the range of typical SDSS images and, therefore, unstudied until now. The present data suggest (although the statistics are inconclusive) that the main difference between the previous profile types is the presence of either a more or a less intense bulge. Half of the Type II-CT galaxies are Sc, whereas half of the Type III-d galaxies are Sb. Finally, Type III-d galaxies have low surface mass density disks (Σ(ΔR_exp) of ∼0.5 M_⊙/pc²) and are bluer – (g − r)₀= 0.32 ± 0.02 – than the other types ((g − r)₀= 0.42 ± 0.02 for Types I and II-CT), suggesting that their disks probably formed later in time.