The REU Experience and Working with CANDELS

My name is Erin O’Leary and I am an undergraduate student pursuing my bachelors in physics and astronomy. This summer I had the opportunity to join the CANDELS team working with Jeyhan Kartaltepe as part of the National Optical AstronomyObservatory’s (NOAO) Research Experience for Undergraduates (REU) program at Kitt Peak National Observatory. I thought I would take the opportunity to share with everyone the story of my summer and the experience I had working with CANDELS.

I am an undergraduate in my senior year finishing my astronomy degree at Macalester College, a small liberal arts school in Saint Paul, MN. Astronomy has been an interest of mine since I could check out stacks of space books at the public library. In high school when I realized I could make a career out of my interest in astronomy, my path was pretty much set.

I spent my previous summer conducting astronomy research at Macalester with Professor John Cannon. I analyzed the stellar populations within a nearby low mass galaxy. This was my first real taste of the research world, and I loved it! I thrived on the independence and the sense of depth that so is different from coursework. I decided I wanted to spend my next summer carrying out astronomy research at a larger science institution. Galaxies in particular piqued my interest and I sought a research experience where I could explore the topic further. I applied to many NSF funded REU programs across the country, and to my excitement, I was offered my top choice position at the KPNO REU!

2012 KPNO and NSO REU students at Kitt Peak

For twelve weeks I lived in Tucson, AZ (quite different than Minnesota!). I spent my time engaging in the undergraduate research experience, which included - yes - lots of research hours spent in front of a computer writing and debugging programs. But what is so great about REU programs like the one I experienced are the vast opportunities to gain exposure to other areas of astronomy and meet cool people. Tucson is a huge hub for astronomy, making it a great place to see all the areas of astronomy in action. Weekly we heard from NOAO or visiting scientists about their area of research. My fellow students and I had tours of the University of AZ mirror lab, NOAO’s optics lab, the McMath-Pierce, 2.1-meter, and the Mayall 4-meter telescopes on Kitt Peak, as well as a week of travel to New Mexico to visit the Very Large Array, the Sloan Digital Sky Survey, and the National Solar Observatory Sacramento Peak facilities. I also spent four nights observing on the 2.1-meter on Kitt Peak. Being able to see (and use) these instruments and then hear about the science resulting from these observations was truly inspiring! I gained so much insight into where my astronomy career can take me. 

Sunset over Kit Peak National Observatory this summer. 

Now onto my work with CANDELS! Before this summer, I had not heard of CANDELS. I was quickly amazed by the quantity of data and science coming out of this project, which made me even more excited to be part of it! 

As I mentioned above, my summer research focused on understanding the role that galaxy mergers and interactions played in galaxy evolution. A few related posts are here and here. Galaxy mergers are beautiful and dynamic phenomena and seen as important drivers of galaxy evolution. Merging galaxies are rare now, but are believed to have played a larger role earlier in the universe. My work involved identifying these galaxy mergers.

CANDELS data are unique and exciting in that they probe higher redshift objects allowing us to view light whose wavelength has been stretched in the expanding universe. What was once visible as optical light is now observable in the infrared. This is essential for accurate galaxy morphology classification. My project was a first look at galaxy mergers at higher redshift (greater than z ~ 1). This can also raise some difficulties in merger identification. As we look at higher redshift galaxies, signature merger features can become faint and more difficult to detect.

I began my work familiarizing myself with the mechanisms of galaxy evolution, galaxy morphology classification, and the scheme that CANDELS has adapted in classifying morphologies. It was a flood of new concepts to me. I spent a fair amount of time classifying these galaxies and debating with myself whether something constituted a merging system. Simply the number of galaxies we were dealing with and the uniqueness of each galaxy blew me away. 

CANDELS images showing a sample of visually identified galaxy mergers.

I then set to work on analyzing the results of the visual morphology classifications of the CANDELS data covering the GOODS-South field. This is a catalog of 7,628 galaxies, each classified visually by about 3-6 people, which means a lot of things to keep track of! Sorting through the data, it was fascinating yet frustrating to compare the classifications that each person had assigned to a given galaxy. 

From this data set, I created selection criteria to choose systems that were merging. Visually, mergers appear to have undergone an interaction evident by an irregular structure, tidal features, double nuclei, or asymmetries. We selected a conservative catalog of galaxies we were pretty certain were mergers. For each identified galaxy merger we collected additional information by matching them to their redshift and mass. We looked for trends in the mass, mass ratio (for interacting pairs), and redshift to tell us about our merger sample.

It is satisfying to look back and see how much I learned this past summer. I felt that my work was just a tip of the iceberg. It was difficult to part ways with my project after those 12 weeks when I knew there exists so much more data and discovery on the horizon. With four more CANDELS fields, it will be very exciting to hear about future outcomes!

So what’s next for me? I am spending my current semester studying abroad at the University of Oslo in Norway and using the opportunity to squeeze extra astrophysics courses into my undergraduate years. When I return in January, I will present my summer research at the AAS meeting in Long Beach, CA. This will be followed by graduation in the spring of 2013. My future plans certainly involve attending graduate school for astronomy.