Deep optical image of the giant low surface brightness galaxy Malin 2, obtained with the Two-meter Twin Telescope (TTT) at the Teide Observatory. The image reveals previously unseen faint stellar structures and diffuse features around the galaxy. Credit: Junais et al. 2025 / TTT.
Astronomers at the Instituto de Astrofísica de Canarias (IAC), using the 2-meter robotic Two-meter Twin Telescope (TTT) at the Teide Observatory, have obtained the deepest optical images ever taken of Malin 2, one of the largest and faintest spiral galaxies in the Universe.
These ultra-deep observations have revealed previously unseen structures, including several diffuse stellar emissions and a striking, elongated spiral-like feature, hinting at past interactions with other galaxies.
The team has also identified a potential ultra-diffuse dwarf galaxy (UDG) about 400,000 light-years from Malin 2, which could be its first known satellite UDG. “Discovering such faint structures around this galaxy was only possible thanks to the exceptional depth and quality of the new TTT images,” says Junais, researcher at the IAC linked to the European ExGal-Twin project and lead author of the study. “It’s like uncovering a hidden history written in the faint light of the galaxy’s outskirts.”
The results suggest that galaxy interactions and tidal processes may play a much larger role in shaping giant low surface brightness galaxies like Malin 2 than previously thought. The faint spiral arm and diffuse stellar features align with structures in the galaxy’s gas distribution, further hinting at its complex dynamical past. These findings show that even the most apparently tranquil and isolated galaxies can have turbulent histories.
Based on these results, the researchers plan to carry out follow-up deep observations of the gas content and its kinematics to confirm the origin of the stellar structures revealed in Malin 2. They also aim to observe more giant low surface brightness galaxies through ultra-deep imaging to determine whether such faint features are common in these types of galaxies or if Malin 2 is an exceptional case. “By pushing the limits of how faint we can see, we are opening a new window into the processes that shape the formation of such enormous galaxies over billions of years”, concludes Junais.
TTT and the ExGal-Twin project
The Two-metre Twin Telescope (TTT) is a robotic facility operated by the Canary Islands-based company Light Bridges, consisting of four telescopes in total: two 2.0-metre twin telescopes and two 0.8-metre complementary telescopes, all designed to operate in a coordinated and fully robotic manner. This architecture makes the TTT one of the most versatile and powerful medium-sized observatory systems in Europe.
ExGal-Twin: Excellence in Galaxies is a project funded by the European Union through the Horizon Europe programme (WIDERA). Coordinated by IAC researcher Johan Knapen, ExGal-Twin aims to strengthen the research capacity, profile and impact of the IAC in the study of galaxies by establishing strategic alliances with prestigious institutions such as the University of Groningen (Netherlands), the CNRS-Observatoire Astronomique de Strasbourg (France) and the ICC at Durham University (United Kingdom).
Article: Junais et al. “Deep imaging of the galaxy Malin 2 shows new faint structures and a candidate satellite dwarf galaxy”, Astronomy & Astrophysics (A&A), 2025. DOI: https://doi.org/10.1051/0004-6361/202556569
Contact at the IAC:
Junais (in English), junais [at] iac.es (junais[at]iac[dot]es)
Ignacio Trujillo, trujillo [at] iac.es (trujillo[at]iac[dot]es)
