I’m an ESA Research Fellow at the Space Telescope Science Institute (STScI) in Baltimore, MD, USA, and a member of the SH0ES team. My research focuses on the astronomical distance ladder and the measurement of the Hubble Constant H0 with Cepheid stars.
My research focuses on astronomical distance measurements using Cepheid stars with the goal of a 1% determination of the Hubble constant H0. The current tension between the local measurement of H0 based on Cepheid and Type Ia supernova distances (H0 = 73.17 ± 0.86 km/s/Mpc by the SH0ES team) and its value inferred from the Λ-CDM model calibrated with CMB data in the early universe (H0 = 67.4 ± 0.5 km/s/Mpc) has reached a 5σ significance. This intriguing discrepancy, which has been recently confirmed with JWST observations of Cepheids, provides growing hints of new physics beyond Λ-CDM.
The first rung of the SH0ES distance ladder is the calibration of the Cepheid Period-Luminosity relation (or Leavitt law) with geometric distances. Then, Cepheids are used to solve for the peak SNIa luminosity. Finally, SNIa in the Hubble Flow directly measure the expansion rate of the universe, H0.
I am working on improving the primary calibration of Cepheids in the Local Group, in particular with parallaxes from the Gaia satellite in the Milky Way (Breuval et al. 2020). I am also interested in reducing the systematic uncertainties in Cepheid distances, for example the metallicity dependence (Breuval et al. 2021, 2022). Recently, I used HST to observe Cepheids in the Small Magellanic Cloud (SMC) in order to increase the number of geometric calibrators for the distance ladder and improve the H0 measurement (Breuval et al. 2024). Following a similar method, I measured the most precise distance to the M33 galaxy (Breuval et al. 2023) which should provide an additional anchor when geometric measurements become available. Finally, I also started investigating different methods of distance measurement such as the Tip of the Red Giant Branch (TRGB) and Carbon stars (the J-region Asymptotic Giant Branch, JAGB), which can substitute Cepheids in the distance ladder (HST GO-17520).
Link to all publications (ADS)
Breuval et al. (2024) - Small Magellanic Cloud Cepheids Observed with the Hubble Space Telescope Provide a New Anchor for the SH0ES Distance Ladder
Breuval et al. (2023) - A 1.3% Distance to M33 from Hubble Space Telescope Cepheid Photometry
Breuval et al. (2022) - An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt Law
Breuval et al. (2021) - The Influence of Metallicity on the Leavitt Law from Geometrical Distances of Milky Way and Magellanic Cloud Cepheids
Breuval et al. (2020) - The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations
Email: lbreuval [at] stsci.edu
Address: Space Telescope Science Institute
3700 San Martin Drive
Baltimore, MD, 21218, USA
