Dark matter makes up about 85% of all matter in the universe. Ordinary matter absorbs, reflects and emits light, but dark matter cannot be seen directly, making it difficult to detect. Its existence can be judged by its gravitational effect on the visible matter that makes up stars, planets, and other objects in space.

Galaxies are composed of these two types of materials. Dark matter is dispersed in halos, which are massive structures that surround galaxies, while ordinary matter is mostly found in the central regions where most stars are located.

Traditionally, observational studies of galactic evolution have focused on the role of ordinary matter, even though it constitutes a relatively small fraction of the galaxy’s mass. Theoretical predictions about the impact of dark matter on the evolution of galaxies have been made for decades. However, despite numerous efforts, there is no definitive opinion on this issue.

Now, research carried out by the IAC team has managed to confirm, for the first time, through observations the influence of dark matter on the evolution of galaxies. The study was published in the journal Nature Astronomy.

Laura explains: “Dark matter has an obvious effect on galaxies because we can measure it, but the effect we found on galaxy evolution is what has been suggested, even though we don’t have the techniques to study it observationally.” explains Laura. Scholz Diaz is a PhD student at IAC and first author of the paper.

To study the effects of dark matter, the team focused on the difference between the mass of stars in a galaxy and the mass that can be determined from its rotation, called the total dynamic mass.

Research has shown that the age, metal content, morphology, angular momentum and formation rate of stars depend not only on the mass of these stars but also on the total mass, that is, the dark matter component is included. this is consistent with halo mass estimates.

“We found that in galaxies with equal stellar masses, stellar populations behave differently depending on whether the halo contains more or less dark matter, that is, the evolution of the galaxy from its formation to the present day varies with the halo it is in. If it has a more or less large halo, the evolution of the galaxy over time is different and this will be reflected in the properties of the stars it contains,” adds Ignacio Martin. IAC researcher Navarro, who co-authored the paper

In the future, the team plans to measure stellar populations at different distances from the center of the galaxy and show whether the dependence of stellar properties on the dark matter halo persists at all radii. The next step of the research will allow us to examine the connection between the dark matter halo and the large-scale structure of the universe.

“These dark matter halos are not created separately, but are interconnected by filaments that form part of a large-scale structure called the cosmic web,” says Scholz. “The mass of a halo appears to change the properties of its galaxy, but this may be a consequence of each halo’s position in the cosmic web. In the coming years we want to see the impact of this large-scale structure on the context we are studying,” he explains.

This work is based on 260 galaxies of CALIFA (Calar Alto Legacy Integral Field Area), an international project in which IAC is actively involved, under the leadership of Jesus Falcon Barroso, another co-author of the paper.

“This research provides spectral information and provides an unprecedented spatial coverage of galaxies,” he says. “These galaxies were observed in a high-resolution configuration to obtain detailed measurements of their kinematic properties, which allowed us to study the motions of the stars very precisely and thus infer the total mass of the galaxies.”