Current Research

21cm Radio Cosmology

Supervised by Eloy de Lera Acedo and Dominic Anstey, and funded by the STFC, I am working on developing Bayesian data analysis techniques for the mitigation of systematics and calibration of the REACH radio telescope.

Time-Varying Systematic Mitigation

Using Gaussian Processes we developed a method of mitigating the effects of unmodelled systematics on our ability to fit for the 21cm global signal (Kirkham et al. 2023). Here we found that by using GPs to fit for time covariances in the model residuals increased our uncertainties in the parameter estimation, generally improving the error of our fits when compared with the standard REACH pipeline (Anstey et al. 2021, 2023).

Calibration

I am continuing work on the calibration of the REACH receiver (Roque et al. 2021, Razavi-Ghods et al. 2023).

Undergraduate Research

You can read my undergraduate thesis here.

The Hubble Tension and Cepheid Systematics

Gaia Parallaxes

The modern SH0ES method of calculating the Hubble constant uses parallaxes from the Gaia program as an anchor in the first rung of their distance ladder however a systematic error has been found in the data (Lindegren et al. 2021b, hereafter L21b). By investigating the effectiveness of the suggested correction to the parallaxes using the relative difference between cluster member star parallaxes, π_*, and the median parallax of the cluster, π_c, I am investigating there are any residual errors after L21b correction which may have an effect on the SH0ES value of H₀.

Two-rung Distance Ladder

While the usual SH0ES method uses a three rung method of calibrating redshifts from supernovae distances and cepheid distances, it is possible to remove the supernovae distances and calibrate redshifts directly from cepheid distances. Without any corrections due to peculiar velocities, this yields a Hubble constant which is consistent with Planck's CMB value. I am investigating how correcting for peculiar velocities changes the resulting value of H₀ and whether other factors such as a possible local underdensity (or Local Hole) need to be considered.

Galactic Reddening

The physics of dust reddening is still poorly understood, and it may be possible the the standard law of dust reddening, A_V = 3.1 E(B-V), may need to be modified. By fitting main-sequence models to Gaia G, G_BP, G_RP and UBV photometry of open cluster stars, I am attempting to determine whether the reddening law needs to be changed to include a distance dependence. If found, this distance dependence could have an impact on the calibration of Cepheid distances and hence the value of the Hubble constant (for example, Mortsell et al. 2021).