Leah Bigwood

Leah Bigwood

Cosmology & Astrophysics PhD student at the Institute of Astronomy, University of Cambridge.

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portfolio

publications

Evidence for episodic black hole growth of reionization-era quasars observed with Magellan/FIRE

Published in Monthly Notices of the Royal Astronomical Society, Volume 529, Issue 4, pp.3511-3520 , 2024

Observations of high-redshift quasars hosting billion solar mass black holes at z>6 challenge our understanding of early supermassive black hole (SMBH) growth. In this work, we conduct a near-infrared spectroscopic study of 19 quasars at 6.2<z<7.5, using the Folded-port InfraRed Echellette (FIRE) instrument on the 6.5-meter Magellan/Baade Telescope. We estimate the single-epoch masses of the quasars SMBHs by means of the MgII emission line and find black hole masses of M_BH ~(0.2-4.8) x 10^9 solar masses. Furthermore, we measure the sizes of the quasars proximity zones, which are regions of enhanced transmitted flux bluewards of the Ly-alpha emission line, ionized by the quasars radiation itself. While it has been shown that the proximity zone sizes correlate with the quasars lifetimes due to the finite response time of the intergalactic medium to the quasars radiation, we do not find any correlation between the proximity zone sizes and the black hole mass, which suggests that quasar activity and the concomitant black hole growth are intermittent and episodic.

Recommended citation: Bigwood, L. et al. (2024). "Evidence for episodic black hole growth of reionization-era quasars observed with Magellan/FIRE" Monthly Notices of the Royal Astronomical Society, Volume 529, Issue 4, pp.3511-3520. 1(1).
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Weak lensing combined with the kinetic Sunyaev Zel’dovich effect: A study of baryonic feedback

Published in arXiv:2404.06098, 2024

Extracting precise cosmology from weak lensing surveys requires modelling the non-linear matter power spectrum, which is suppressed at small scales due to baryonic feedback processes. However, hydrodynamical galaxy formation simulations make widely varying predictions for the amplitude and extent of this effect. We use measurements of Dark Energy Survey Year 3 weak lensing (WL) and Atacama Cosmology Telescope DR5 kinematic Sunyaev-Zeldovich (kSZ) to jointly constrain cosmological and astrophysical baryonic feedback parameters using a flexible analytical model, “baryonification”. First, using WL only, we compare the S8 constraints using baryonification to a simulation-calibrated halo model, a simulation-based emulator model and the approach of discarding WL measurements on small angular scales. We find that model flexibility can shift the value of S8 and degrade the uncertainty. The kSZ provides additional constraints on the astrophysical parameters and shifts S8 to S8=0.823+0.019−0.020, a higher value than attained using the WL-only analysis. We measure the suppression of the non-linear matter power spectrum using WL + kSZ and constrain a mean feedback scenario that is more extreme than the predictions from most hydrodynamical simulations. We constrain the baryon fractions and the gas mass fractions and find them to be generally lower than inferred from X-ray observations and simulation predictions. We conclude that the WL + kSZ measurements provide a new and complementary benchmark for building a coherent picture of the impact of gas around galaxies across observations.

Recommended citation: Bigwood, L. & Amon, A. et al. (2024). "Weak lensing combined with the kinetic Sunyaev Zeldovich effect: A study of baryonic feedback." arXiv:2404.06098. 1(1).
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talks

teaching

Teaching experience 1

Undergraduate course, University 1, Department, 2014

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Teaching experience 2

Workshop, University 1, Department, 2015

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