This occasional series focuses on members of the Frontier Fields team. It highlights the individuals, their jobs, and the paths they took to get to where they are today.
Dan Coe, ESA/AURA Astronomer, in front of the first Frontier Fields image, Abell 2744.
What is your position? What are your responsibilities?
I am an ESA/AURA astronomer at the Space Telescope Science Institute (STScI) in Baltimore. I use gravitational lensing to search for distant galaxies in Hubble and Spitzer Space Telescope images. I am the gravitational lens model coordinator for the Frontier Fields program. I also work to support astronomers’ use of Hubble’s Advanced Camera for Surveys and the Near-Infrared Camera on the upcoming James Webb Space Telescope.
How did you get involved with the Frontier Fields program?
In 2012, working on the Cluster Lensing And Supernova survey with Hubble (CLASH), I discovered a candidate for the most distant galaxy yet known, MACS0647-JD. Its light took about 13.4 billion years to get here, so we see it as it was long ago. We are looking 97 percent of the way back to the Big Bang. Back then, galaxies were much smaller, just 1 percent the size of our Milky Way, and had yet to form grand spiral structures.
MACS0647-JD is more distant than any of the galaxies discovered in the Hubble Ultra Deep Field (UDF), even though Hubble stared at the UDF for much longer: a week vs. four hours for the infrared images. This demonstrates the power of gravitational lensing. Galaxy clusters enable us to see fainter light from galaxies in the distant universe.
Gravitational lensing had been used often by astronomers, but its power had yet to be fully exploited. No one had taken ultra-deep images of a galaxy cluster with Hubble or Spitzer. I advocated for this to a committee convened by former STScI Director Matt Mountain. And now it has become a reality in the Frontier Fields program led by Jennifer Lotz. The ultra-deep images of galaxy clusters are revealing the faintest galaxies ever studied, magnified by gravitational lensing.
How do astronomers study gravitationally lensed galaxies?
The distant galaxies in these images are most typically magnified by factors of between 2 and 10. To properly study these galaxies, we need estimates of their magnifications from gravitational lens modeling. By studying the observed deflections and distortions of background galaxies, astronomers build up a model of each galaxy cluster’s mass distribution (primarily dark matter) and the resulting lensing magnifications.
For the Frontier Fields, five groups of astronomers from around the world collaborated to gather the best possible data on all six clusters and produce gravitational lensing models. I coordinated these efforts and processed their model submissions for all astronomers to use. This lens modeling work is unprecedented both for its collaborative nature and the accessibility that all astronomers now have to the magnification estimates. With deep Frontier Fields imaging now in hand, astronomers are able to study the lensing in much more detail and are producing the best dark matter maps and lensing models ever.
Are there specific parts of the program that you’re proud to have contributed to?
I helped Jennifer Lotz select the six Frontier Fields clusters—with a lot of input from other astronomers. I had hoped my babies would do well! So far they have, and I am proud.
Left: Frontier Fields Hubble image of Pandora’s Cluster, Abell 2744. Right: Lensing magnifications (color) and distortions (swirls) of distant galaxies according to one model produced by Johan Richard and the “CATS” (Clusters As Telescopes) team.
How did you first become interested in space?
Mom was a space geek, as she tells it. She can still name the Mercury Seven [NASA’s first astronaut class]. She drew celestial bodies on the ceiling above my crib and hung a poster of Van Gogh’s “Starry Night” on my wall. She sat me on her lap to watch Carl Sagan’s “Cosmos” and to read the companion book. She took me outside to enjoy eclipses and meteor showers. And she held me in her arms and cried on my head as we watched the first Shuttle launch. I remember always being awestruck by the immensity of the universe. And I knew I wanted to work on everything.
This picture of Dan and his mom was taken when the future astronomer was just 5 months old.
What specifically is your educational background?
I went to Browne Academy elementary school, Thomas Jefferson High School for Science and Technology, Cornell University for my B.S. in Applied & Engineering Physics—with a concentration in astrophysics—and Johns Hopkins University, right across the street from STScI, for my Ph.D. in astronomy.
What particularly interested you in school or growing up? What were your favorite subjects?
Growing up, I loved math, puzzles, games, and eventually computer programming. The latter proved especially useful for my career since we write many programs to analyze our Hubble images and other data.
“What about poetry?” Mom would ask. She and my father had studied art, literature, and history. As a smart-aleck kid, I insisted all of that could be explained by mathematics. But as I grew up, I grew to appreciate the poetry in Carl Sagan’s explanations of our universe. I became more curious about all of the physical and personal forces that brought us to where we are and take us where we are going. And all of this, in time to meet my partner Kate Welch, a Shakespeare scholar, who gives me a deeper appreciation for both poetry and history. Turns out I should have listened to my mother all along!
How did you first get started in the space business?
I followed Carl Sagan to Cornell, but unfortunately I never got to meet him. He was too sick to teach my freshman year. During my senior year, astronomers announced new supernova results suggesting the existence of dark energy. Carl Sagan had taught us we are all made of star stuff. But then we learned that the universe is mostly made of something very different: dark matter and dark energy. Astronomy had humbled humanity yet again. I think I always planned to go to grad school for astronomy, but those exciting results really sealed it for me.
Once in grad school at Johns Hopkins, my advisor Narciso Benitez started me working on mapping dark matter in galaxy clusters by modeling gravitational lensing, and measuring distances to galaxies in new Hubble ACS images, including the UDF. He was a constant source of inspiration as I tackled tough analysis problems. I followed him to Granada, Spain, where I finished my Johns Hopkins Ph.D.
After three years at NASA’s Jet Propulsion Laboratory and Caltech in Pasadena, I am now back in Baltimore at STScI. My colleagues and I here are fortunate to work with Adam Riess, one of the Nobel Prize winners from that inspiring dark energy discovery in 1998.
What do you think of the Hubble results, or the impact that Hubble has on society?
I am proud to be contributing a small part to Hubble’s great legacy. In addition to my Frontier Fields work, I am leading a large new Hubble program called RELICS to observe 41 more lensing galaxy clusters. Complementary to the Frontier Fields, RELICS is casting a broader net with shallower imaging. Our goal is to find the best and brightest distant galaxy candidates for more detailed study with current telescopes and with the James Webb Space Telescope.
Hubble has filled us with wonder and taken us back in time, almost all the way back to the Big Bang. By flipping through Hubble’s scrapbook, we can relive 97 percent of the history of the universe. James Webb will tell the tale of our cosmic origins in the first galaxies.
I can’t say I really comprehend the immensity of the universe any more than I did as a child. But I have appreciated new details, and I remain awestruck. The universe teaches us to be humble yet proud, and most of all, I think, grateful. Humble, as an insignificant speck in the vast cosmos. Proud that we have come so far and can begin to comprehend it. And grateful that we have the privilege to witness and explore so much of it.
Is there a particular image or result that fascinates you?
We named one of our cats after the Carina Nebula. The Hubble + CTIO Blanco color image of this stellar nursery is a masterpiece—the most beautiful astronomy image I’ve seen. Our other cat is named Maggie, after Queen Margaret in Shakespeare’s Henry VI; she has a “tiger’s hide.”
Dan calls this picture of the Carina Nebula “the most beautiful astronomy image I’ve seen.” This 50-light-year-wide view of the nebula’s central region shows a maelstrom of star birth and death. The mosaic was assembled from 48 frames taken with Hubble’s Advanced Camera for Surveys, with information added from the Cerro Tololo Inter-American Observatory in Chile.
What outside interests—e.g., hobbies, service, dreams, activities—could you share that would help others understand you better?
When I was around 10, my father and I started playing duplicate bridge at a local club on Saturdays. Many of the other partnerships would argue with one another over their play, but not us. Dad and I did our best, celebrated our good plays, and learned from our mistakes, but never got angry with one another. My parents’ unwavering support, pride, encouragement, and engagement of my curiosity have made me the astronomer I am today. I do my best to keep making them proud.
Dan, at the age of 11, poses with his dad and mom.
Is there anything else that you think is important for readers to know about you?
I feel very fortunate to be paid to do what I love. And I have been privileged. Like many others at STScI, I work hard and try to give back in small part by sharing the rich history of our universe with others in Baltimore and with people around the world. I hope you enjoy hearing our stories.
Also see “Spotlight on Jennifer Mack, Research and Instrument Scientist.”