My main research interest is understanding how galaxies have evolved into their current state, in particular how galaxy mergers have shaped that evolution. Interactions between two galaxies of a similar mass (what I’ll refer to as galaxy mergers) drastically alter the star-formation activity, chemical composition, morphology, and central black-hole accretion of galaxies. Our current interpretation of the universe leads us to believe that galaxies may form hierarchically through interactions. I investigate this stage of galaxy evolution by analyzing how galaxies in the process of merging, and how post-merger galaxies, differ from those which are undisturbed.
SDSS gri – images of galaxies undergoing different stages of an interaction. Image credit: www.sdss.org
Given the rarity of merging events in the local universe, observational studies of galaxy mergers are dependent on massive surveys to collect a sufficient sample of galaxy mergers. Mergers themselves can last hundreds of millions of years, so to reconstruct the merging process I also need a large sample to collect galaxies at different interaction stages (see above). Until recently such surveys were limited to a single spectrum collected for each galaxy, overlooking the non-uniform effects of mergers over a range of internal spatial scales.
My current research utilizes integral field spectroscopy, where spectral information is collected across a galaxy’s surface, to quantify the spatial changes in a galaxy as a result of an interaction. Using the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, I can analyze maps of star-formation and metallicity for merging galaxies within the survey. Using well established relationships between star-formation rate surface density, metallicity, and stellar mass surface density, I then measure the offsets in SFR (ΔΣSFR) and metallicity (ΔO/H) for merging galaxies with respect to the general star-forming population.
An example of ΔΣSFR and ΔO/H maps for three post-merger galaxies, derived from PIPE3D dataproducts. MaNGA reveals greater variety in the spatial distribution of the star-formation enhancement and metallicity suppression than expected for post-merger galaxies, particularly in the galaxy outskirts.