Studying the evolution of galaxies using bulge-disk decompositions of simulated and observed galaxies

Laura DeGroot

The MOSDEF survey has spectroscopically observed ~1500 galaxies from when the Universe was only 1.5 – 4.5 billion years old. By combining the spectroscopic information obtained from the survey, such as star formation rate, metallicity, and stellar mass, with morphological measurements, including structural parameters like size and Sérsic index, we can further understand how galaxies evolve with time.  Previous studies (Lang et al. 2014, Brennan et al. 2016) have found that there is tentative evidence of a correlation between structural and spectroscopic parameters. However, pairing the deep rest-frame optical spectroscopy completed by the MOSDEF Survey team with deep multi-wavelength data sets available, the relation between spectroscopic properties and structural properties (morphology) can now be well studied for these distant galaxies. 

Morphologically, we aim to accurately separate the light of the bulge from the disk of the disk galaxies in this sample by modeling the light distributions of the galaxy components. By comparing the measured morphological properties of the bulges of the galaxy sample to other galaxy properties, we can to try to understand how galaxy bulges form and evolve in time. To accomplish this, we use GALFIT (Peng et al. 2002, 2010) to model the light using a Sérsic function. However, finding the boundary for the two components is difficult and uncertain. To check our accuracy, we simulate galaxy profiles with multiple components using GALFIT and insert them into a Hubble Space Telescope image. By running our modeling code on these new simulated galaxies, we can test the agreement of the known properties and measured properties of the sample. We can therefore be more confident in our morphological analysis by understanding the accuracy, as well as uncertainty, of our bulge-disk decompositions of the galaxy sample. This bulge-disk decomposition technique and measured uncertainty are then applied to analyzing galaxies in the MOSDEF survey to study galaxy evolution. 

Figure 1: GALFIT results for two MOSDEF galaxies. The parameters from the models are used to understand the morphology of the galaxies.