Research News
NARIT Researchers Analyze 1.1 Million Galaxies
to Better Understand Galaxy Evolution
Dr. Suttikoon Koonkor, an astrophysicist at the National Astronomical Research Institute of Thailand (Public Organization) (NARIT), has revealed the results of a study of more than 1.1 million galaxies aimed at understanding how galaxies have evolved throughout the 13.8-billion-year history of the Universe. The research also found evidence suggesting that current models of galaxy formation may require revision. The study was published in Monthly Notices of the Royal Astronomical Society on February 23, 2026.
Understanding how galaxies form and evolve remains one of the major questions in modern astronomy. Galaxies come in many forms. Some, like the Milky Way, are spiral galaxies that actively form new stars, while others have smooth elliptical shapes and exhibit much less star-forming activity. Studying how these different types of galaxies evolve over time helps astronomers understand how the large-scale structures of the Universe form and how the processes that create stars and planets ultimately lead to environments capable of supporting life.
However, studying galaxy evolution is far from straightforward. The processes involved can take billions of years, making it impossible to directly observe the complete evolution of a single galaxy. Instead, astronomers study large populations of galaxies at different stages of cosmic history and use those observations to reconstruct how galaxies change over time. Because the speed of light is finite, light from distant galaxies takes time to reach us. Looking farther into the Universe therefore allows astronomers to look farther back and observe earlier stages of cosmic history.
One of the most important statistical tools used in these studies is the luminosity function, which describes the number density of galaxies at different brightness levels. According to simple models in which galaxy evolution is driven solely by the gravitational influence of dark matter, the abundance of galaxies should closely follow the distribution of the large dark matter structures known as dark matter halos. However, observations tell a more complex story. Astronomers find both more faint galaxies and different numbers of bright galaxies than these basic models predict. These discrepancies suggest that additional physical processes play an important role in shaping galaxy evolution.
Researchers believe that two of the most important processes are feedback from supermassive black holes at the centers of galaxies, known as Active Galactic Nuclei (AGN), and supernova explosions. Both can release enormous amounts of energy into their surroundings, heating gas and preventing it from collapsing to form new stars. These effects are thought to play a major role in determining the number, size, and brightness of galaxies observed in the Universe today.
To investigate the effects of these processes, Dr. Suttikoon Koonkor participated in the analysis of more than 1.1 million galaxies from the Physics of the Accelerating Universe Survey (PAUS). The survey was carried out using the 4.2-meter William Herschel Telescope on La Palma, Spain, and provides observations of galaxies across a large fraction of cosmic history.
PAUS estimates galaxy distances using a technique known as photometric redshift measurement, which compares the brightness of galaxies across many wavelength bands. As the Universe expands, light from distant galaxies is stretched toward longer wavelengths, a phenomenon known as redshift. One of the survey’s key strengths is its use of 40 narrow-band filters, which provides more accurate distance estimates than many conventional broad-band surveys. This allows astronomers to study galaxies from a time when the Universe was only about four billion years old, covering more than 70 per cent of cosmic history.
The researchers found that current theoretical models agree well with observations from the present day back to approximately eight billion years ago. However, clear differences emerge between eight and ten billion years ago. Further analysis showed that uncertainties in galaxy distance measurements can significantly affect the measured luminosity function, particularly at the bright end. Such uncertainties can lead to incorrect conclusions about the role of AGN and supernova feedback in galaxy evolution, highlighting the importance of accurate redshift measurements in studies of galaxy formation and evolution.
The team also found evidence for an excess population of faint galaxies compared with predictions from current theoretical models. Similar results have been reported by other recent surveys, including DESI. Because both PAUS and DESI cover large survey areas, the researchers are confident that the observed excess is not simply the result of cosmic variance arising from large-scale fluctuations in the galaxy distribution.
This finding may indicate that feedback from AGN and supernovae is less effective than current models suggest. If so, more gas may remain available for star formation, allowing galaxies to produce more stars than previously expected. The result points toward the need for further refinement of theoretical models of galaxy formation and evolution.
Meanwhile, NARIT researcher Dr. Nicha Leethochawalit is investigating a related question at an even earlier stage of cosmic history. Using observations from the James Webb Space Telescope (JWST), she studies galaxy populations that existed only a few hundred million years after the Big Bang.
Her research suggests that there are more extremely bright galaxies in the early Universe than current theoretical models can explain. This may indicate that stellar population synthesis models, which are used to interpret light emitted by stars in galaxies, require further refinement when applied to the early Universe. Alternatively, It may suggest that star formation in the first generations of galaxies proceeded differently from what astronomers currently understand.
Together, these studies are helping astronomers build a clearer picture of how galaxies form and evolve over cosmic time. Their findings provide valuable constraints for improving theoretical models and may ultimately lead to a deeper understanding of how the structures that make up today’s Universe come into existence.
Compiled by : Dr. Suttikoon Koonkor and Dr. Matipon Tangmatitham
References: [1] https://arxiv.org/pdf/2511.16042
[2] https://arxiv.org/pdf/2601.09948
[3] https://wwwmpa.mpa-garching.mpg.de/galform/