Graduate Student Highlights

By Carter Rhea (Chair, CASCA Graduate Student Committee)
(Cassiopeia – Summer 2020)

Each month, the GSC highlights the work of an outstanding Canadian graduate student by sharing their work with our members. Since the launch in February of 2020, we have highlighted four students from around the country.

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Christian Thibeault — L’Université de Montréal

Solar flares are sudden and intense releases of magnetic energy stored in the corona, causing the plasma to heat up to 10 million degrees Kelvin. The radiation and highly energetic particles emitted from these events can damage our satellite communication network and pose a health threat to astronauts. It has been suggested since the early 1990s, by E.T. Lu and collaborators, that solar flares are a manifestation of unobservable small scale magnetic reconnection processes that can be simulated by simple lattice models, called “avalanche models”. The goal of my master’s research project is to evaluate the predictive capabilities of these models in making solar flare forecasting. We first studied the stochastic behaviour of many avalanche models, and now are integrating data assimilation using X-ray observations of flares to improve our prediction methods.

Figure 1 – Cartoon of a physical interpretation of a coronal loop accumulating energy through the twisting of its footprints. (Strugarek et al. 2014)

Mallory Thorp — University of Victoria

Mallory’s research investigates how galaxies change as the result of a major galaxy merger, when two galaxies of comparable size interact and merge to form a single galaxy. To understand the kpc-scale changes resulting from a merger event, she uses Integral Field Spectroscopy (IFS) measurements from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. IFS provides a spectrum for every pixel on an image of a galaxy, allowing her to examine how spectral dataproducts like star-formation rate (SFR) vary across a galaxy.

Figure 2 contains 3 examples of post-merger galaxies from MaNGA (1st column), along with maps of their SFR surface density (2nd column). By comparing the maps of SFR from post-merger galaxies to those of isolated galaxies, she can quantify the change in SFR as the result of the merger event.

The 3rd column shows enhancements in SFR as a result of the merger in blue, whereas a deficit in SFR compared to an isolated galaxy are shown in red. On average post-mergers experience a galaxy-wide enhancement in SFR, like the 2nd and 3rd post-mergers. Variations from this, like the notable suppression of SFR in the outer regions of 1st post-merger, could indicate different progenitor qualities and orientations can alter how effectively star-formation is enhanced.

This work was completed by myself, under the supervision of Sara Ellison (both of us CASCA members!).

Figure 2

Lingjian Chen — Saint Mary’s University

My research is a galactic environment study. Dense galactic environments, such as galaxy groups and clusters, are thought to be formed through hierarchical mergers. Spatial distribution of satellite galaxies can be a good indicator for galaxy evolution in such environments.

We study the radial distribution of satellites around isolated massive central galaxies using data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP) and the CFHT Large Area U-band Deep Survey (CLAUDS). Thanks to the large area, 6-band photometry and good depth of the combined survey, we were able to identify ~5000 centrals in a redshift range of 0.3<z<0.9 and also identify satellites around them down to stellar mass of 109.5 solar mass.

Our results show that satellite number density distribution can be described by an NFW profile (Navarro+1995, usually for mass density profile in dark matter halos) on scales greater than 100 kpc but deviates from it within that scale. This feature is seen out to z=0.9, it was previously found in studies at low redshift (e.g. Tal+2012). We have also investigated the dependence of the distribution on satellite and central properties such as mass and star-forming level. We concluded that the mechanism of shaping satellite distribution can probably be related to a combination of dynamic friction and tidal stripping when they are orbiting in the dark matter halo, but more detailed simulation or modelling are needed to understand better the physical process.

Figure 3 shows our satellite galaxy selection. Central galaxy is indicated by the yellow circle, potential satellites are circled in green, and red circle indicates our selection radius for satellites (700 kpc). Central galaxies were identified by mass and isolation criteria. Satellites were selected by photo-z difference and a circular aperture (basically a cylindrical selection centred on central galaxy). Number of satellites selected here were then corrected for contaminating background objects.

Figure 3

Figure 4 shows surface number density of satellite galaxies (averaged) around one central galaxy, after correction for background objects. The solid line is the best fit curve and can be separated into NFW component on large scale and Sersic component on small scale (dotted and dashed lines).

Figure 4

Farbod Jahandar — L’Université de Montréal

The main quest of Farbod’s work is unravelling the chemistry of our nearest stellar neighbours. This includes high-resolution observation and examination of M dwarfs as the most numerous type of star in our Galaxy and the smallest and coolest kind of star on the main sequence. Such an analysis impacts many fields of astrophysics, in particular, the determination of exoplanet radius that depends on a reliable estimate of the host radius that in turn depends on its chemical characteristics.

To achieve this goal, Farbod uses high-resolution data from the SPIRou instrument, which is one of the world-leading instruments at the Canada-France-Hawaii telescope. Then he uses chemical spectroscopy methods on the obtained data for the determination of the chemical abundance of different elements in the outer atmosphere of M dwarfs. This will be a critical component for a better understanding of the chemical evolution of M dwarfs and also can heavily contribute to chemical and dynamical improvements of the current synthetic stellar models.

Figure 5

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