Research

My primary area of research is polarization studies using radio observations – namely, looking at fast radio bursts, pulsars, and star forming regions.

Origins of fast radio bursts

Fast radio bursts (FRBs) are extragalactic, short duration radio transients that were first discovered in 2007. Since coming online in 2018, the Canadian Hydrogen Intensity Mapping Experiment (CHIME; see the image by Andre Renard below) has detected thousands of FRBs, becoming the foremost observatory for FRB science. However, the local environments and emission mechanisms for producing FRBs remains elusive.

Many theories of FRB emission invoke a magnetar (a highly magnetized neturon star) origin – as such, one aspect of my research focuses on studying the polarization properties of FRBs as a means to decipher their origins. For instance, the change in the polarization angle of the emitted light as a function of time and frequency can tell us about the region of the magnetosphere it was emitted from and the surrounding environment. I study these properties on a population level to determine if all FRBs originate from similar emission mechanisms and environments or whether there are multiple, distinct modes for producing FRBs.

As the polarized radio emission from FRBs propagates from the source to us on Earth, the polarization angle of the radio waves is rotated by gas and magnetic fields in the intervening media (this effect is characterized by the “rotation measure” or “RM”). A large contribution to the RM is due to our own Galaxy and, therefore, to accurately study the magnetized environments around FRBs, we must have good estimates for the Milky Way’s RM contribution within FRB observations. One way to do this is to use background, polarized light from many radio galaxies near the FRB on the sky and interpolate the RM at the sky-position of the FRB. Further, the FRBs themselves provide a useful backlight for looking at the foreground Galactic magnetic field they propagate through.

Fast radio bursts as probes of the Universe

Regardless of the specific origins of FRBs, they serve as useful probes of intervening media because their signal is affected by the coincident gas and magnetic fields. In a recent study, I showed that FRBs could be used to create a map of the dispersion measure in the Milky Way and of the Galactic magnetic field. In order to do this, we need to use statistical inference methods to recreate continuous fields from discrete lines of sight toward FRBs probing the Galaxy. Further, we also describe steps to help distinguish Galactic and extragalactic contributions to the observed FRB signal, which is one of the largest challenges when using FRBs to study intervening media. The figure below summarizes how well we can reconstruct the expected Galactic thermal electron distribution using 50,000 FRBs and applying some corrections that we derive in the paper.

Star Formation

Another one of my research interests is to study the role of magnetic fields in star formation – particularly, as molecular clouds collapse into dense cores that will be the progenitors to protostars. Using the Green Bank Ammonia Survey (GAS), I studied the shapes and rotation of dense cores and how they align with the local magnetic field, as traced by dust polarization. Below, you can see the dense core elognation, velocity graident direction, and magnetic field orientation for one of the cores in our sample.

In total, I studied 399 dense cores (the largest such dynamical sample) and found that the classical model of star formation is in disagreement with our results, which instead favour a low-magnetization triaxial core model. Further, we found that more evolved cores (identifieid as “protostellar”) tend to be preferentially elongated more perpendicular to the local magnetic field. This suggests that, either, (i) these cores were aligned this way early on in their formation and that fact allowed them to collapse into protostars, or (ii) the core contraction occurs in magnetically-regulated environments or where core growth occurs through anisotropic accretion.