LBC sophomore studies simulated galaxies
Claire Kopenhafer is a Lyman Briggs sophomore studying physics. This summer she is working on a research project titled "Spatially Resolved Spectroscopy of Distant Galaxies" with Dr. Brian O'Shea of Lyman Briggs College.
My research with Dr. O’Shea began last fall as part of the Honors College’s professorial assistantship program. As a theoretical and computational astrophysicist, Dr. O’Shea conducts his research using computer simulations. My first few months were spent familiarizing myself with the software used to analyze these simulations. As time went on, the details of my current project began to emerge and I was fortunate enough to be awarded funding from Briggs to work on my research over the summer.
Astronomers can determine a lot about a galaxy by using spectroscopy. Spectrographs measure how many photons of varying wavelengths come from an object such as galaxy or star. Every element will emit or absorb different wavelengths of light, and so the kinds of elements present in an object and their abundance can be determined. In addition, because of the velocities of objects and the Doppler effect, and the general expansion of the universe, the wavelengths corresponding to an element are measured as longer than they should be. This is called redshift, and can reveal an object’s speed and distance, among other properties.
Until recently, astronomers could only measure the spectrum of a galaxy as a whole. But to fully understand what’s going on in different parts of a galaxy and how galaxies evolve, one spectrum per galaxy isn’t enough. Enter the integral field unit, or IFU, a new observational tool that allows multiple spectra to be taken across a galaxy like pixels in a picture, and the focus of my research project. The properties determined from a galaxy’s IFU spectra can be plotted in maps, but the trouble lies in interpreting these maps: sometimes the patterns that emerge don’t clearly show what’s going on in a galaxy. My research seeks to alleviate these ambiguities by making synthetic IFU observations from simulated galaxies. It’s a lot easier to determine what is going on in a simulated galaxy than in a real, very distant one because, in a simulation, all the data about a galaxy is right in front of you. The mock observation and its maps can be compared to pictures made straight from the data of the simulation to find out what’s going on.
The first part of this project, programming the software tools that will make the mock observations, only has a few more pieces to go. Then the second part—using the tool to “observe” different simulations—can take place. Optimistically, the first part will be done by the end of summer semester. But a programming task can start out sounding easy and then quickly gobble several days of your time. This has especially been true when I’ve had to figure out how to place things within the three dimensional space the simulation occupies. Accomplishing things such as where to cast data-gathering “light rays” and where to place the different fibers that comprise an IFU have been puzzles of 3D geometry. It gets even trickier when I have to make sure my methods work for when the direction of observation isn’t in line with an axis, and the plane the fibers occupy become slanted. I’ve used vectors and the basics of calculus three in every one of my solutions, and because an important idea in math is generalizability, this approach lets me write one section of code that can be applied to all cases.
I try to be very careful with what I code. A computer will always do what you tell it to, but that may not always be what you wanted. This project has been my first experience with astrophysics, and as such, I don’t know everything that needs to be accounted for in terms of the physics of my code. What unit is this data in, what unit does it need to be in? Do I need to take this and this into account? What details don’t matter as much, and which ones do? I always make sure to double check what I’m doing with Dr. O’Shea. The thing I fear most is making a slight mistake in a calculation that doesn’t look obviously wrong but skews the results.
The greatest thing about this project is that it has the potential to be very useful. Dr. O’Shea and I are already talking with an astronomer who is very interested in our work, hoping it can help her interpret her own IFU observations. Over the next few years, the MaNGA survey will taking IFU observations of roughly 10,000 galaxies, and the hope is that this project will give insight into this data as well. In addition, the program I am developing will be contributed back to the open source software package it uses, so that anyone can use it and build on it.
Unlike other experiences I’ve heard about, I’m not just playing some small part in a lab; this is my own project, and being able to work on it over the summer has made it more fun. I can spend more of my time working, and less time doing homework when I’d rather be doing research. It can be challenging at times, but the challenges make it worthwhile! Especially when, after all the pieces fall in place, a picture emerges that looks just exactly as it should, and maybe even better than hoped for. Summer semester may be wrapping up, but the real questions are only just starting to be asked.