The ESA’s Euclid space telescope has been in space for just over a year, investigating some of the deepest mysteries of the cosmos. By observing cosmic structures up to a distance of 10 billion light-years, the observatory will chart the evolution of the Universe, attempt to constrain the influence of Dark Energy, and study the morphology of galaxies. In terms of galaxies, Euclid will attempt to answer the question of why the Universe contains such a variety of galaxies, characterized by size, shape, and colours.
Astronomers have long wondered if the morphologies of different galaxies are linked and what evolutionary mechanisms are responsible. Since the first Quick Data Release 1 (Q1) happened back in March, astronomers now have a catalog of more than 1 million large galaxies that could help address these questions. Along with their teammates, Maximilian Fabricius and Roberto Saglia of the Max Planck Institute of Extraterrestrial Physics (MPE) conducted a study that identified some unusual astronomical phenomena that are shedding light on how galaxies evolve in our Universe.
A century of studying galaxies has taught astronomers a great deal about the diversity of galaxies in our Universe, which led to classification schemes like the Hubble Sequence (aka. the “Morphological Tuning Fork”). This scheme categorizes galaxies into four types: elliptical, lenticular, spiral, and irregular, based on their morphologies. At the same time, scientists use classifications such as dwarf, active, and “dusty” to describe their colors and compositions. According to this scheme, galaxies begin their lives as disk-like, blue, star-forming systems that evolve into spirals, eventually merging with others to form elliptical galaxies.
As they exhaust their supply of star-forming gas and dust and larger stars exit their main sequence and become red dwarfs, the galaxies will become darker, redder, and dustier. Determining how galaxies undergo this evolutionary process, and how their environment (alone or in large clusters) influences their shape and ultimate fate, has remained unanswered. Thanks to Euclid’s wide field of view and sharp optics (which were built with significant contributions from the MPE) (https://www.mpe.mpg.de/7756075/news20210929), the space telescope was able to image more than 1.2 million large galaxies with exceptional depth and resolution in its first year alone.
*The “Morphological Tuning Fork” of galaxy classifications, re-created using Euclid’s high-resolution images from data release Q1. © ESA/Euclid/Euclid Consortium/NASA, diagram by J.-C. Cuillandre, L. Quilley, F. Marleau*
While the Q1 release only covers about 63 square degrees of images and catalogs (or about 0.5% of the total dataset the six-year mission will provide), the data has already enabled a remarkable range of studies that have demonstrated Euclid’s capabilities and revealed rare astronomical phenomena. When examining the data from Q1, Fabricius and Roberto Saglia identified hundreds of early-type galaxies that exhibited secondary nuclei, which could be the seeds of future supermassive black hole (SMBH) binaries. Said Fabricius in an MPE press release:
Euclid offers an unprecedented combination of sharpness and sky coverage — it will map the entire extragalactic sky. For the first time, we can systematically study how the shapes and central structures of galaxies relate to their formation history on truly cosmic scales.
The most massive black holes lie at the centres of giant elliptical galaxies and are thought to grow primarily through mergers with other supermassive black holes. By detecting and analysing secondary nuclei, Euclid enables us to explore how these enormous black holes continue to grow—and how their growth influences the galaxies that host them.
In another study led by the Euclid Collaboration, co-led by Dr. Christoph Saulder (an MPE postdoc), astronomers identified a rare population of 65 galaxies exhibiting highly-ionized emission lines. These signatures are typically associated with extreme phenomena, such as Active Galactic Nuclei (quasars), high stellar winds (shock fronts), and massive stars that have shed their outer layers (Wolf-Rayet stars). These findings and others released by the Euclid Consortium are providing crucial insights into how galaxies coalesce, the energetic feedback mechanisms, and other factors shaping their evolution.
Thanks to its sensitivity, Euclid is also revealing that the most common types of galaxies in the Universe are dwarf galaxies, which were typically too faint to study in detail. Conventional wisdom holds that larger spirals form from the merger of dwarf galaxies, as evidenced by the Milky Way’s interaction with its small, closest neighbors—the Small and Large Magellanic Clouds (SMC/LMC) and the Canis Major Dwarf Galaxy. Euclid is already revealing interesting things about these structures, including their morphologies (58% ellipticals, 42% irregulars) and the presence of compact blue cores or globular clusters in some.
Once Euclid has completed its six-year nominal mission, it is expected to reveal far more about the dynamics that shape galaxies, including how new stars are born, galactic interactions and collisions, and how black holes form and influence stellar formation.
Further Reading: MPE