Leah Bigwood
I’m Leah Bigwood, a third year PhD student in Astronomy based at the Institute of Astronomy, University of Cambridge (and sometimes also found at Peyton Hall, Princeton University!). I enjoy working at the intersection between astrophysics and cosmology: learning how to disentangle the impact of galaxy formation physics on our measurements of cosmology. Ultimately this will get us closer to cosmology’s goal; truly understanding the Universe’s evolution and its contents.
About
I graduated from Durham University in the UK in 2022 with First Class Honours in MPhys: Physics and Astronomy. There I was fortunate to win a number of awards; including the D. A. Wright Prize for outstanding perfomance by a Final Honours candidate, the Durham Physics Award for Outstanding Achievement, and the Level 4 Prize for Theoretical Astrophysics. In addition to my Master’s thesis within the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey, I won funding to undertake a number of projects supervised by researchers at other institions. This included my work ‘Evidence for Episodic Black Hole Growth of Reionization-Era Quasars observed with Magellan/FIRE’, which was carried out in collaboration with Anna-Christina Eilers at the Massachusetts Institute of Technology. In 2022 I began my PhD at the Institute of Astronomy, University of Cambridge, where I am supervised by Prof. Alexandra Amon and Prof. Debora Sijacki. In 2023 Alexandra became an Assistant Professor at Princeton University, so I have been lucky to spend some extended visits at Peyton Hall in Princeton.
My research
My PhD research thus far has focused on ‘baryonic feedback’. Baryonic feedback encompasses the physical processes associated with baryons, which can cool and heat gas, and redistribute the total matter in the Universe. The dominant baryonic feedback process is feedback from Active Galactic Nuclei (AGN). It is believed that AGN have the power to eject baryons beyond the virial radius of galaxies to the outskirts of groups and clusters, therefore significantly impacting the Universe’s small-scale matter distribution. In order to extract unbiased cosmology from observables such as weak galaxy lensing, we need to accurately model the Universe’s matter distribution. The impact of baryonic feedback effects to redistribute the small-scale matter in the Universe however remains largely unknown, with simulations making wildly varying predictions on the amplitude of the effect.
My work aims to get to the bottom of how we should model baryonic feedback in cosmological analyses, and understand whether it is currently biasing our weak-lensing derived cosmology measurements. If so, baryonic feedback could be responsible for the so-called ‘S8 Tension’ in cosmology, and I am interested in testing the possibility of this solution. Regardless, baryonic feedback results in significant precision loss in our cosmological measurements. To truly get the most out of future weak lensing survey (such as the upcoming Vera C. Rubin Observatory) and make dark energy constraining measurements, we need to understand just how powerful baryonic feedback is, and how much it is impacting our measurements.
I enjoy working directly with observational data, and recently co-led a joint DES cosmic shear + ACT kinetic Sunyaev-Zel’dovich analysis. This work addressed the following questions;
Do different baryonic feedback models give the same weak lensing derived cosmology result?
Can we jointly analyse weak lensing with measurements of the kSZ effect to constrain the baryonic feedback model parameters?
Can we use weak lensing + kSZ as a new benchmark for hydrosimulations: do we have a consistent picture of feedback effects?
I also work with hydrodynamical simulations, to understand the degeneracies which result in differing predictions of the extremity of baryonic feedback. I am currently working on a modified AGN feedback model in the FABLE simulation suite, labelled XFABLE. XFABLE is able to predict feedback of greater extremity than fiducial FABLE, providing a hint that feedback could indeed have the potential to bias our current weak lensing cosmology and be responsible for the S8 Tension.
Contact me
I am always very enthusiastic to hear from anyone interested in my science, whether that is relating to an outreach opportunity or a potential collaboration! Please get in touch via:
email: lmb224@cam.ac.uk