I am primarily interested in understanding how structures in our Universe came to be, and how they can be used to answer fundamental questions such as what is our Universe made of? what are dark matter and dark energy? where do we come from? These questions have led me to study and probe the connection between visible and dark matter, using both analytical, numerical and statistical models. My main findings are summarized below, all my publications are publicly available on arxiv and referenced on NASA ADS.

  • Turbo-charging galactic outflows
  • The imprints of early mergers on galaxies like our Milky Way
  • How cosmological merger histories shape galactic outskirts
  • Re-igniting star formation in tiny galaxies (see also this press article.)
  • How diverse are extremely faint dwarf galaxies
  • Genetic modifications: a new method to study the formation of halos and galaxies

  • Turbo-charging galactic outflows

    Explosions of supernovae within a galaxy can drive powerful outflows of gas, which are key to reducing fuel for further star formation and regulate the growth of the galaxy over cosmic time.

    In this work, we study how limited numerical resolution impacts our understanding of simulated galactic outflows. Introducing a new technique to gradually increase numerical resolution in the outflow, we find that a more accurate treatment of their thermodynamics systematically increases the mass and energy carried away by the outflows. This boost, by up to a factor five, is achieved without modifying any astrophysical models within the galaxy, strongly motivating a better treatment of outflows when modelling the regulation of galaxies over cosmic time.

    The imprints of early mergers on galaxies like our Milky Way

    Recent results from the GAIA telescope have revealed radially-biased, low-metallicity stellar debris around the Sun. This is most commonly interpreted as the remnant traces of the collision between a dwarf galaxy and the proto Milky Way 10 billion years ago.

    In this work, we use a new suite of high-resolution cosmological simulations of Milky-Way-like galaxies to test this hypothesis. Using the genetic modification, we grow and reduce the mass of the impacting dwarf galaxy, fixing the cosmological large-scale structure and the total stellar and dynamical mass of the Milky Way.

    Comparing the consequences of these different histories, we find distinct galaxy morphologies today, but similar stellar debris whether the collision is made extremely minor or major. We explain this degeneracy through the growing importance of stars formed during a starburst with another, even earlier merger, and show that debris observed today likely come from multiple mixed origins. This makes it more chalenging to reconstruct our Galaxy's past, but more informative about how galaxy formed more than 10 billions yeards ago.

    How cosmological merger histories shape galactic outskirts

    The diffuse stellar halo surrounding galaxies provides a unique window on the formation and evolution of galaxies. It is shaped by the accretion and stripping of stars previously formed in smaller galaxies that are deposited in distinct patterns in galatic outskirts as in NGC 474 above.

    It therefore traces both the host’s past merger history and the star formation histories of dwarf galaxies unobservable directly. However, for a given galaxy, the details of its merger history are stochastic: they are seeded by random early universe perturbations inflated to cosmological scales. This stochasticity couples to the strongly non-linear response of the galaxy to generate diversity in stellar halo observables.

    In this work, we introduced a new approach to study how this interplay shapes stellar halos. By varying each aspect independently with flexible methods, we showed how diverse cosmological scenarios yield extensive scatter in stellar halo content and structure (greatly summarized on astrobites here). We further isolated the distinct sensitivity of this scatter to galaxy formation physics within the host central galaxy, and within the small building blocks to the halo. This opens new prospects to constrain star formation and evolution at different galactic mass-scales with stellar haloes.

    Re-igniting star formation in tiny galaxies

    Small, very faint dwarf galaxies are typically observed without traces of recent star formation - most of their stars were born 10 billions of years ago before the Universe was heated by its accumulating starlight. A growing number of exceptions to this scenario have been noticed however; but how galaxies such as Leo P (picture above) and Leo T have managed to sustain the formation of new stars until the present day remains an open question.

    In this work, we show, using numerical simulations, that dwarf galaxies can grow just enough to slowly accrete fresh gas, eventually fueling the re-ignition of their star formation after a few billions of years. The generic nature of this uncovered mechanism predicts that many similar galaxies to Leo P and Leo T should exist and are waiting to be discovered by future, more sensitive instruments. These results caught the specialized press' attention, and will soon be communicated to the general public.

    How diverse are extremely faint dwarf galaxies

    With improving instruments over the years, astronomers have kept discovering both fainter and more diffuse dwarf galaxies (such as Eridanus 2 in the above picture). These discoveries have constantly pushed back our understanding of how small, diffuse and faint a galaxy is allowed to be in our Universe.

    In this work, we combine cutting edge numerical simulations of dwarf galaxies with a new approach, genetic modifications, to probe and predict the expected diversity in the masses and sizes of dwarf galaxies. Our simulations recover galaxies similar to currently observed ones, but also showcase the formation of very faint, highly diffuse dwarfs outside of the detection capabilities of current facilities. Despite our repeated efforts, our results predict that many more dwarf galaxies are yet to be discovered.

    Genetic modifications: a new method to study the formation of halos and galaxies

    Over the course of my PhD, I participated in the development of "genetic modifications", a new approach that allows us to modify specific aspects of a galaxy's cosmological merger history in a controlled way. This enables us to construct a causal account between a galaxy's history and its final observables.

    I first strengthened the theoretical foundations of the method, and then implemented a new kind of modifications to target multiple mergers at once. Tools to construct and craft genetically modified initial conditions are now publicly available to the community.

    Outreach and news

    Into the Cosmos, Oxford

    Big day at the office today to welcome more than >800 visitors for the open day of Oxford Astrophyics . Lots of stimulating discussions around galaxy formation and cosmology triggered by our simulation movies.

    Marie Curious Workshop, Warwick

    It's always fun to chat and present astrophysical science to school kids, particularly for the cause of motivating more women to work in STEM .

    Public lecture, Staffanstorp

    It was a pleasure to answer the invitation from the Rotary Klubb in Staffanstorp to present the mysteries of our Universe to their members. Although virtual due to the ongoing 2020-pandemic, we had engaging discussions about our Universe (and the others). Even got a gift from Ronny Hård as a thank you!

    Christopher Skinner Prize for Outstanding postgraduate research

    I am very grateful and honored to have been awarded the Christopher Skinner prize. This prize commemorates a postdoctoral researcher who died prematurely, by annually acknowledging outstanding research performed by graduate students in the Departent of Physics and Astronomy at University College London.

    Festival Astr'auvergne

    During summer 2018 in Auvergne, I participated to an astronomy festival organized in part by Nicolas Laporte. Beautiful sceneries and great weather (rare enough in this region) made the moon eclipse very enjoyable. It was a pleasure to contribute with a public lecture on dark matter, an interview on local radio and a 3-day summer school for children aged 6 to 15 years old. Once again, this was done in cooperation with this great group of friends, the Astro-jeunes society.

    Re-opening of the KLB building at UCL

    On April 2018, we officialy re-opened our new building at UCL (we moved in only 6 months ago). The main attraction was not the building itself but David Attenborough, living legend of the BBC, who gave an incredibly inspiring talk at 91 years old. We explained what our research was about and what the Universe is made off to him and a variety of high profile people. Quite an inspiring day !

    Astronomy School at the London French School

    I spend two days in May 2017 at the French High School , once again talking about astronomy and physics, to 13 years old children. Many different activities were organized by the astrophysicists of Astro-jeunes society, including visible, H-alpha and radio observations of the Sun, a planetarium and a “northern lights” simulator.

    Your Universe Festival

    Over a week in March 2017, we welcomed over 500 pupils at UCL to learn about astronomy. The event is called Your Universe and is run every year. I was involved in the “Dark matter and cosmology” stand, explaining that most of our Universe is dark and the different methods of inferring that dark matter is there, such as gravitational lensing.

    Academic travel and events

    I actively participate in academic events, conferences and workshops to discuss recent results within astronomy and astrophysics. Following is a list of community events I have contributed to, by either presenting my results or helping to organize them.

    Collaborative projects

    I work closely with Harley Katz , Oscar Agertz, Andrew Pontzen, Justin Read, and Tjitske Starkenburg. You can find our latest works here, and several of our large team-based efforts I am an actively involved in:

    About me

    I am originally from France where I did most of my studies. I studied aerospace engineering at ISAE Supaéro in Toulouse (yes it is rocket science) where I learnt how to build spacecrafts including my own cubesat which has now been launched and is free floating in space.

    Working within the large bureaucratic collaborations of space engineering was not quite for me, so I joined the theoretical physics forces, first at Imperial College London with Jonathan Pritchard and afterwards on a PhD with Andrew Pontzen. I then joined Lund University as a postdoctoral researcher working with Oscar Agertz, before securing the Beecroft Fellowship in Cosmology at the University of Oxford. My CV contains a more formal description of my background and you can find a list of my papers on arxiv.

    And when I am not working, I tend to be at sea, not sleeping for a few days to race other sailboats far from the coasts.