Victor Rufo Pastor

I am a PhD student in the Galaxy Formation Group within the Division of Astrophysics at Lund University. My position is funded by the Knut and Alice Wallenberg Stiftelse (PI: Oscar Agertz, Wallenberg Academy Fellowship). I am carrying out my PhD research in collaboration with my supervisors, Dr.~Oscar Agertz and Dr.~Santi Roca Fábrega. My research focuses on galaxy formation and evolution, with particular emphasis on the properties of the circumgalactic medium (CGM) and on how galactic disc formation correlates with CGM processes such as gas flows and hot corona.

Exploring the Universe: Galaxies, Discs, and the Circumgalactic Medium

Despite the remarkable progress in astronomy with powerful telescopes like the James Webb Space Telescope (JWST) and the Vera Rubin Observatory, we still face a fundamental limitation: observations capture only a single moment in time. They cannot show us directly how galaxies evolve over billions of years.

To bridge this gap, scientists use cosmological simulations, which combine physics, models, and computational techniques. These simulations let us create “virtual universes” on our computers, filled with data we can use to test ideas and explain what we observe. Each simulation is like a movie of galaxy evolution, allowing us to watch frame by frame from the early universe to the present day.

My topic connects disc formation with the CGM.  But what does that mean?

The formation and growth of galaxies is extremely complex. It depends on many interconnected processes, from star formation and supernova explosions to gas flows, galaxy mergers, and the influence of dark matter. Capturing all of these mechanisms in simulations is a major challenge, and it requires careful comparisons with real observations as well as with other simulation models.

My research focuses on the connection between the formation of galactic discs and the circumgalactic medium (CGM).

The CGM is a vast, multiphase envelope of gas that surrounds galaxies. Discovered in the mid-20th century, it contains gas with many different densities, temperatures, and ionization states. The CGM acts as both a supplier and a regulator: it feeds gas into galaxies while also controlling how that gas is accreted.

This mysterious structure is central to some of the biggest open questions in astrophysics, such as why galaxies form stars at the rates they do, where the “missing” baryons are, and why the expected amount of heavy elements (metals) is often absent. In short, the CGM plays a key role in shaping how galaxies grow and evolve.

At the same time, galaxies themselves enrich and exchange gas with the CGM, creating a constant interplay between the two. The state of the CGM often mirrors the state of the galaxy it surrounds, making them deeply interconnected.

One big question to answer

My work aims to extract physical insights from simulations to better understand the evolution of galaxies and the formation of their discs. Ultimately, we want to answer questions such as: How do galaxies and their discs form? How accurate is our current theoretical knowledge? And what does this mean for our broader understanding of the universe?

One major focus is how gas enters galaxies through the CGM. Broadly, gas can accrete in two modes: cold or hot. In the hot mode, associated with the formation of a large, hot gaseous halo called the corona, gas flows in slowly and steadily, helping to build galactic discs. In the cold mode, however, gas plunges rapidly into the galaxy, sometimes disrupting the disc instead of supporting it.

Understanding how the hot corona forms and what role it plays in galaxy evolution is a key step toward answering the bigger question: how do galaxies, including our own Milky Way, come to be the way they are today?