"This research demonstrates how the chemical information preserved in stellar atmospheres can be used as a fingerprint to reconstruct the evolutionary history of a galaxy," explains Sara Vitali, PhD candidate in Astrophysics at UDP.
An international team of astronomers, led by the Institute of Astrophysical Studies at Universidad Diego Portales, has successfully reconstructed the chemical evolution of the Sagittarius dwarf spheroidal galaxy with an unprecedented level of detail. This ancient companion of the Milky Way is currently undergoing dissolution due to its interaction with our galaxy.
The research titled “The Pristine Inner Galaxy Survey (PIGS) XI: Revealing the chemical evolution of the interacting Sagittarius dwarf galaxy”, soon to be published in the specialized scientific journal Astronomy & Astrophysics (A&A), is the core work of the doctoral thesis by Sara Vitali, a PhD student in Astrophysics at Universidad Diego Portales, who is set to complete her studies in June of this year. The study is based entirely on observations conducted in Chile, using the FLAMES spectrograph of the European Southern Observatory (ESO), installed on the Very Large Telescope (VLT) in the north of the country.
“This study presents the most extensive and homogeneous high-resolution optical analysis to date of stars in the central core of the Sagittarius galaxy,” explains Sara Vitali, who holds a degree in Physics from the University of Turin (Italy) and a Master’s in Astrophysics from the University of Potsdam (Germany). A total of 111 giant stars were studied, carefully selected from a catalog of over 50,000 potential members, thanks to data from the international Pristine Inner Galaxy Survey (PIGS), of which Vitali is a member.
The observations made it possible to measure the abundance of up to 14 different chemical elements per star (including sodium, magnesium, calcium, barium, and europium) and to estimate their ages. This allowed the researchers to trace a chronological evolution of the galaxy’s star formation process.
The results show that Sagittarius had a richer and more prolonged evolutionary history than previously thought. During its first billion years, it formed stars rapidly and efficiently, leaving behind an ancient, metal-poor stellar population. But most revealing is that this activity did not stop: the galaxy continued forming stars in later episodes, even as recently as 4 billion years ago.
This demonstrates that, despite having lost much of its gas due to interactions with the Milky Way, Sagittarius managed to preserve favorable conditions for continuing to generate new stellar generations. “This research shows how the chemical information preserved in stellar atmospheres can be used as a fingerprint to reconstruct the evolutionary history of a galaxy,” adds Vitali.
From UDP, renowned astronomer Paula Jofré—director of the PhD Program in Astrophysics and Vitali’s thesis advisor—emphasizes the structural importance of the work: “This is the final paper of Sara’s PhD, and her work clearly shows how we are building strong talent in stellar spectroscopy here in Chile—an area with a long-standing tradition internationally, and one that is gradually reaching a critical mass in our country. This will allow us to develop a wide range of projects related to stars, from studying stars as hosts of planets to using them as tracers of galactic histories".
At the same time, the study has direct implications for broader research on the history of galaxies. “Sara’s work has been important in laying the groundwork for what we are developing in galactic phylogenetics. It is one of the studies that has contributed tools, data, and specific cases to the Millennium Nucleus ERIS, which I lead. Now, with this sample of chemical data from Sagittarius, we plan to examine how phylogenetic trees compare with those we have built for the Milky Way, allowing us to contrast the evolutionary histories of both galaxies,” adds Jofré.
This study is the result of a collaboration between Álvaro Rojas, Principal Investigator, and Paula Jofré, Director—both from the Millennium Nucleus ERIS. It was initiated by the ERIS team and strengthened through spectral analysis collaboration with Claudia Aguilera, also a researcher at the same nucleus. In addition to its scientific impact, the work highlights the potential of Chile’s astronomical infrastructure. “The observations were carried out entirely using telescopes located on national territory, taking advantage of the privileged skies of the north. And although it was an international collaboration, much of the work was developed at UDP, which demonstrates our country’s growing capacity to lead world-class research in astrophysics,” concludes Vitali.