Akanksha Bij

Queen’s University

Akanksha Bij is a doctoral candidate at Queen’s University, working with Dr. Kristine Spekkens. Her current research focuses on understanding galaxy formation and evolution in a cosmological context using neutral Hydrogen (HI) observations of gas-rich low-mass galaxies in the local universe. Akanksha is involved in forecasting an observing strategy for a new radio telescope, the Canadian Hydrogen Observatory and Radio-Transient Detector (CHORD), which is currently under construction and will carry out untargeted HI galaxy surveys in the upcoming years.

During her master’s research, Akanksha worked with Dr. Laura Fissel to understand the interplay between magnetic fields and stellar feedback in the star formation process. They used dust polarimetry observations to infer the plane-of-sky magnetic field orientation on sub-parsec (i.e filament) scales within a high-mass star-forming region known as RCW 36, located in the Vela C giant molecular cloud. This region is of particular interest because it has an ionized (HII) bipolar nebula powered by a massive star cluster which may be impacting the surrounding magnetic field. To determine if this was the case, Bij et al. 2024 quantified the relative alignment between the inferred magnetic field orientation and the orientation of elongated structures observed in several datasets such as dust emission, column density, temperature, and spectral line intensity maps.

Interestingly, the results show a bimodal trend where structures which are primarily observed with dense gas tracers show a statistically significant preference for perpendicular alignment relative to the magnetic field, while structures probed by photo-dissociation region (PDR) tracers tend to align preferentially parallel relative to the magnetic field. A PDR is the interfacing boundary between an ionized HII region and the surrounding molecular gas cloud. An instance of this bimodal trend is shown in the figure below. The longer wavelength (70500 m) dust maps, which primarily trace the dense molecular gas features, are found to have negative Zx values, indicating a preference for perpendicular alignment relative to the magnetic field. In contrast, the short wavelength (35 m) dust maps, which primarily trace warm gas structures heated by stellar feedback near the PDR, show positive Zx values, indicating a preference for parallel alignment. This finding suggests that the interstellar magnetic field may have been dynamically important and set a preferred direction of gas flow at the time that RCW 36 formed, resulting in a dense ridge developing perpendicular to the magnetic field. However, on filament-scales near the PDR region, stellar feedback may be energetically dominating the magnetic field, warping its geometry and the associated flux-frozen gas structures, causing the observed the preference for parallel relative alignment.

You can find the paper here.

The Projected Rayleigh Statistic, Zx, as a function of the wavelength of the dust map. Zx measures the statistical significance of the relative alignment between the magnetic field orientation and orientation of structures in a map (Jow et al 2018). A value |Zx|>3 is considered statistically significant, where Zx < 0 values indicate a preference for perpendicular relative alignment and Zx > 0 indicate a preference for parallel relative alignment.