Abstracts Astronomy & Space Science

STUDYING THE MILKY WAY THROUGH ITS EXTRAGALACTIC ANALOGS

by Timothy Licquia

The Universe is teeming with galaxies, which are complex structures with a broad range of colors, shapes, and sizes. We reside within the Milky Way (MW), just one example of this population, allowing us to study its stars and gas, and hence the physical mechanisms that shape galactic properties, in intimate detail. Unfortunately, our inside-out view prohibits us from measuring the MW's light as an integrated source, and perhaps more problematic is that dust in the interstellar medium shrouds most its light from view. Consequently, our knowledge of the global characteristics of the MW, and hence how fits among the galaxy population, has remained very limited. This thesis is focused on employing modern statistical techniques as well as preexisting Galactic and extragalactic data to overcome these challenges. A key aspect of this work is the development of a hierarchical Bayesian meta-analysis technique for better constraining properties of our Galaxy that have been studied by many authors and for which there exist extensive observational data, but may be prone to large systematic uncertainties. Applying this machinery yields new estimates of the MW's mass properties, including its star formation rate and total stellar mass, as well as its exponential disk scale length measured from both visible and infrared starlight. Additionally, this thesis presents a new method for identifying a sample of MW analog galaxies from extragalactic data in order to determine properties of our Galaxy that are all but impossible to observe directly. Herein, this technique yields new estimates of the MW's photometric properties – i.e., its global color and luminosity at visible wavelengths, as measured from across cosmic distances. This work culminates with new, accurate investigations of how the MW fits into a variety of extragalactic contexts, which quantitatively demonstrates that in several ways the MW is not the prototypical spiral galaxy it was recently thought to be. Notably, the MW most likely lies in the sparsely populated “green-valley” region of the galaxy color-magnitude diagram. Furthermore, comparing the MW to spiral galaxy scaling relations reveals that it is extraordinarily compact versus its peers.