Go Ahead, Jump

The ballerina is an avatar of certain qualities—among them the ambition, skill, and courage to take bold leaps. Offstage, ballet lover Rachel Theios has infused those same characteristics into her budding research career in astronomy. Pursuing her first publication as a Caltech graduate student, she has shown the vision and bravery to question some of the fundamentals of her field.

“It turns out that our measures for the rate of star formation are not doing a great job,” she says.

Theios aims to help explain how galaxies come to be, and better understanding how the stars within them are born is one part of that project. Ultimately, her investigations may create knowledge about the structure of the universe itself. She can take scientific risks with assurance thanks to Caltech’s unique resources for astronomical discovery, the guidance of faculty, and philanthropic backing as a Troesh Family Distinguished Scholar.

Theios works with Chuck Steidel, Caltech’s Lee A. DuBridge Professor of Astronomy, to move her studies forward using one-of-a-kind tools: a pair of advanced spectrographs at the W. M. Keck Observatory and a massive set of records from observations of the distant, primordial universe.

“It’s really interesting to do a statistical survey instead of looking at individual galaxies,” Theios says. “My adviser spent decades building up the dataset I’m using for my thesis. No one else has anything like this.”

Back to Basics

In classic Caltech style, she and her colleagues started with the fundamentals.

“Looking at whether galactic properties correlate with each other is something basic you can do,” she says. “And then if they don’t, that’s interesting.”

Astronomers such as Theios seek to determine the properties of galaxies—including how quickly stars formed—at different points in the history of the universe. The raw material for this research is observations of different wavelengths of light.

A sample of the data Theios has produced using the MOSFIRE spectrograph installed at the W. M. Keck Observatory. The rectangle on the bottom is a spectrum returned by MOSFIRE. To paraphrase, it shows the amount of light at each wavelength coming from a galaxy named Q2343-BX182, 10.2 billion light years away. In the graph, green dashes mark the most telling spectral lines. For example, H-alpha and OIIII, forms of hydrogen and oxygen, respectively, are often emitted by the gas around forming stars.

Each spectrum of light offers its own type of clue. But for the vast majority of galaxies, scientists simply cannot collect all of the spectra they would like to analyze. Instead, for many years, astronomers have used either ultraviolet or optical light as the basis for calculating the rate of star formation, depending on which they were able to measure.

Theios saw an opportunity. In that gargantuan collective dataset, she had access to multiple spectra for many of the same far-off galaxies. Focusing on more than 300 galaxies that formed during the prime cosmic era when stars were born, she compared results applying the two standard methods for determining the rate of star formation. If both were accurate, they should have produced similar estimates. But instead, there was a discrepancy.

They did not agree—a conclusion she knows is likely to attract pushback.

“It is kind of risky for an early-career graduate student to publish a controversial paper. But it is also exciting.”
- Rachel Theios

Support in Her Search

Steidel’s guidance and coaching are helping Theios interpret the story the data tell, with confidence.

“I’m learning to be a better scientist because he has so much experience,” she says. “He doesn’t want me to rush into things. He wants me to think clearly about what everything means.”

Meanwhile, the Troesh Family Distinguished Scholars Fund—created with a gift to Break Through: The Caltech Campaign—helps preclude financial distractions so she can follow her curiosity.

“Thanks to the fellowship, I could do the kind of science I wanted to do without the burden of finding funding,” she says.

Aside from observing galaxies and analyzing massive datasets, Theios relishes the outlet of dancing. As leader of the Caltech Ballet Club, she performs and teaches fellow students. And that pastime just happens to benefit her investigations as well.

“It’s important to develop your creative side as a researcher,” she says. “It helps you to focus and make connections.”

In this case, the connections Theios is making could help keep astronomy on its toes.


Spectra gathered by the MOSFIRE instrument
The first infrared data collected by the MOSFIRE spectrograph at the W. M. Keck Observatory, signifying different chemical abundances in stars and galaxies

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