Vivian Tan

York University

Vivian’s research is on the galaxies that reside within massive clusters at redshifts 0.25 < z < 0.6, in the Hubble Frontier Fields. Clusters are dynamic environments where galaxies interact and quench, which means transitioning from star-forming to quiescent. Quenching processes alter a galaxy’s morphology, which we want to measure not just with their light profiles but through their stellar mass distribution. Mapping where the stellar mass is in a galaxy is usually difficult at z > 0, but the Frontier Fields have deep multiband Hubble photometry. This means resolved stellar mass maps are possible even for galaxies as small as 108 solar masses. Galaxies with such low stellar masses have not been studied in a resolved way at z > 0. Because we can analyze morphology with resolved stellar mass maps, we found that quiescent galaxies which are less massive than 109.5 solar masses are more likely to be disk-dominated (Sersic index ~ 1 to 2), but quiescent galaxies are bulge-dominated above that mass limit (Sersic index of 4 or more). This was only found in clusters but not in the less dense “field” environments. This means different quenching processes must have occurred to transform these galaxies, and these quenching processes depend both on the galaxy’s mass and their environment

This image shows the process of creating the resolved stellar mass maps through a process called SED-fitting. The galaxy is broken up into spatial bins, and a SED is fitted to photometric flux from multiple bands in each of the bins. The fitted SED can reveal what the stellar mass of that region of the galaxy is and putting it all together results in a resolved stellar mass map. Sersic index measurements for the stellar mass are obtained via parametrically fitting a 2-D Sersic profile directly to the map of stellar mass using GALFIT.