Hi. I'm Tobias Géron.

And I'm an astrophysicist at the University of Toronto.

Personal

I'm originally from Antwerp, Belgium. I obtained a BSc in Bio-Engineering from the University of Antwerp (2013-2016). After that, I got an MSc in Bio-Engineering from Ghent University (2016-2018), during which I spent one semester as an exchange student at Yonsei University in South Korea. After graduating, I decided to switch academic fields and I started studying Astrophysics at the University of St Andrews in Scotland (2018-2019). I loved this so much, that I eventually pursued a PhD (or, as it is called there, a DPhil) at the University of Oxford, England (2019-2023). I recently started working as a postdoctoral fellow at the University of Toronto in Canada.

Aside from astronomy, I also really enjoy hiking and being out in nature. Some highlights include climbing Mount Kilimanjaro in Tanzania and through-hiking the Pacific Crest Trail in the USA after I finished my PhD. As you might expect, both trips also included spectacular views of the night sky.

Research

My research during my PhD was mostly focussed on galaxy evolution. More specifically, I looked at how bars, like the one shown to the right, affect star formation and quenching in their host galaxies. The barred galaxy shown here is called "NGC 1300" and is arguably the most famous barred galaxy. More information on this particular galaxy can be found here. Observations have found that bars appear more often in quiescent galaxies. However, it is uncertain whether it is easier to form a bar in a quenched galaxy or if a bar helps to quench its host - basically a chicken or egg problem on galactic scales. Additionally, roughly half of all nearby disc galaxies have a bar, so understanding how they affect their host is important to properly understand the evolution of galaxies as a whole.

A picture of NGC 1300. Credits: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

Historically, people have typically focussed on very strong and obvious bars, such as the ones displayed on the top row of the figure below. This is mostly because they are easier to identify and observe. However, as in turns out, bars come in all shapes and sizes. The bars on the bottom row in the figure below are much fainter and weaker, but they are bars nonetheless. In my first paper, I looked at how both weak and strong bars affect their host. One of the key results was that weak and strong bars seem to be part of a continuum of bar types that vary from weak to strong, with strong bars being able to affect their host more. If a bar is stronger, it will induce more star formation in the center of a galaxy, which in turn will help to quench the galaxy quicker. These results are presented in much greater detail in (Géron et al. 2021).

Various strongly barred galaxies (top row) and weakly barred galaxies (bottom row). Figure taken from Géron et al. (2021).

I have also spent some time measuring how quickly bars rotate within a galaxy (i.e. their "pattern speed") using a technique known as the Tremaine-Weinberg method. In order to do this, I used data from a survey called MaNGA. The cool thing about MaNGA is that it is an IFU survey, which means that it obtains spectra at multiple positions across the face of a galaxy. This means that we have access to reliable kinematic data (i.e. how the stars move) at multiple points for one galaxy. Using this technique, I was able to create the largest catalog of pattern speeds for strongly and weakly bared galaxies to date. One of the interesting results that came out of this study is that the strong bars rotate significantly slower than weak bars. These results, and more, are presented in Géron et al. (2023). Using these kinematic measurements, one can also classify bars into so-called fast and slow bars. Preliminary results show that fast and slow bars affect their host in very different ways. These exciting results will be published soon. This suggests that the kinematics of the bar, as well as the morphology of the bar, plays an important role. If you're interested to learn more about the kinematics of bars, check out this interactive tool. Please note that this tool is still under development.

In order to study strong and weak bars, we first need to identify them in galaxies. This was done using Galaxy Zoo, a citizen science project where volunteers can help scientist by classifying the morphology of galaxies. During my PhD, I helped create the Galaxy Zoo DECaLS and Galaxy Zoo DESI catalogs by downloading and uploading images to the project and aggregating the classifications into a final catalog. This involved working with large amounts of data -- Galaxy Zoo DESI contains a total of ~8.7 million galaxies with reliable morphological classifications!

Here in Toronto, I will continue my research in galaxy evolution. More specifically, I will study the impact that fast and slow bars have on their host galaxies in much greater detail. Additionally, I will help develop software and new research tools for the Transient and Variable Star Collaboration to make research with data coming from Rubin LSST easier and more accessible. Rubin is expected to collect ~20 terabytes of data and generate an estimated ~10 million transient alerts each night, so being prepared for such a huge amount of data is very important.

Publications

Contact

Address:
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
50 St. George Street
M5S 3H4, Toronto, Ontario
Canada