Unfolding the Universe

Universe of stars background
Jeyhan reaching up and touching a starHexagonal graphic with the text Unfolding the universe
RIT astrophysicist puts students first while researching the origins of thousands of galaxies

While speaking with a student over Zoom on a seemingly normal day in April 2021, Associate Professor Jeyhan Kartaltepe received a Slack message with news that would alter her career.

“Oh my god, oh my god, oh my god,” said Associate Professor Caitlin Casey, Kartaltepe’s collaborator from the University of Texas in Austin.

“What’s going on?” asked Kartaltepe. “We got it! We got it,” replied Casey.

The Space Telescope Science Institute (STScI) had just revealed the proposals selected for the General Observer programs for the James Webb Space Telescope’s (JWST) first year of operation. Panels of scientists had winnowed approximately 1,200 proposals into 266 programs approved for the telescope’s first year. The largest was COSMOS-Web, a massive study of thousands of the earliest galaxies in the universe to be led by Kartaltepe and Casey.

Since that day, Kartaltepe’s work with the most powerful observational instrument ever made has gone at light speed. The telescope had a long-awaited launch on Christmas Day 2021, released its first official images in summer 2022, and began collecting data for COSMOS-Web in January 2023. Ultimately, the telescope will help explain the origins of the universe.

“Everything about JWST so far has exceeded expectations,” said Kartaltepe. “The sensitivity is higher than people expected, and that almost never happens. This is better than we could have hoped for.”

Kartaltepe now has her hands full studying data from COSMOS-Web and other large JWST programs, while continuing to bolster her reputation as a teacher and mentor. Her work has gotten the attention of the astronomy community worldwide.

“She is a tremendous asset to RIT,” said Professor Bahram Mobasher, a longtime collaborator from the University of California Riverside. “RIT was already on the map, but she has really done a lot for that program.”

Composite image with 3 researchers looking at an image taken from the james web space telescope

Associate Professor Jeyhan Kartaltepe from RIT’s School of Physics and Astronomy is co-leading COSMOS-Web, a massive study of thousands of the earliest galaxies in the universe.

Credit: Scott Hamilton | Background Image Credi­­­t NASA, ESA, CSA, and STScI

The background image is a mosaic created by some of the first observations for the COSMOS-Web program taken by JWST’s NIRCam from Jan. 5-6, 2023.

Image credit COSMOS-Web/Kartaltepe, Casey, Franco, Larson, et al./RIT/UT Austin/CANDIDE

Evolution as a scholar

Kartaltepe’s interest in studying the evolution of galaxies in the early universe began in earnest while she was an undergraduate astronomy-physics major at Colgate University in the early 2000s.

She secured an internship at STScI and worked on what would become the Great Observatories Origins Deep Survey (GOODS), which used Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and XMM-Newton to survey the distant universe to the faintest flux limits across the electromagnetic spectrum.

These were the most advanced space-borne observatories at the time and allowed astrophysicists to conduct studies across many different wavelengths, including visible light, gamma rays, X-rays, and infrared.

That internship linked her with scientists she still collaborates with today.

She moved on to pursue her master’s and Ph.D. at University of Hawaii at Manoa, where she first heard about the Cosmic Evolution Survey (COSMOS).

The COSMOS survey began in 2002, studying a specific patch of sky to better understand the formation and evolution of galaxies. It began as a Hubble Space Telescope program but has since included imaging by most of the major space-based telescopes and many large ground-based telescopes. The program has grown to include more than 200 scientists in a dozen countries.

 “The person who became my Ph.D. adviser came to recruit students for his research group and told us about COSMOS,” Kartaltepe said. “He said we’re going to look at a million galaxies and see all these things and that just blew my mind away.”

Mobasher, one of the co-founders of COSMOS, said Kartaltepe quickly stood out for her intelligence, vision, integrity, and collaboration skills. The two have collaborated on countless projects over the years, most notably COSMOS and the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), two of the biggest projects in the Hubble Space Telescope’s history.

CANDELS was designed to study “cosmic dawn,” less than 1 billion years after the Big Bang when the universe’s structure began to take shape, and “cosmic high noon,” 2 billion to 4 billion years after the Big Bang when galaxies experienced a major growth spurt.

After earning her Ph.D. in 2009, Kartaltepe spent time at the National Optical Astronomy Observatory as a postdoctoral research associate and Hubble Fellow. She then joined the faculty in RIT’s School of Physics and Astronomy in 2015.

“I really liked the balance that RIT has because teaching is valued and that’s not always the case at some universities,” said Kartaltepe. “I liked that I was asked about teaching and the outreach work I did, as well as my research. The College of Science has a portfolio model where you kind of get to choose your balance, and I find it healthy that everyone’s balance can be different.”

Three scientists discussing with each other appearing to be looking at pictures taken by James Web Space Telescope


Science is for everyone

Kartaltepe said she hopes JWST’s launch and early success can be an energizing moment for the public’s interest in science. She compares JWST’s launch to that of Hubble in 1990.

“Most of the public knows what Hubble is, and I think JWST is quickly becoming that household name, and it’s exciting,” said Kartaltepe. “Seeing the launch and learning about the technology was a point of interest for a lot of people.”

She is working to make sure that excitement is shared by all. A passionate advocate for women in her field, Kartaltepe wants the field to have a different environment than the one she grew up in.

“Ever since I was an undergraduate student, most of my mentors have been men,” said Kartaltepe. “Every supervisor I’ve ever had has been a man. Fortunately, they have all been great and have been very supportive, because not everyone has that. But I want to ensure there are positive women mentors for students and scientists at all stages of their careers.”

Kartaltepe is a former chair of RIT’s Women In Science program and continues to serve on its executive committee. She mentors women and students from other underrepresented populations at the undergraduate, graduate, and postdoctoral research levels.

“She believes that science can be for everyone,” said Isabella Cox ’20 (physics), ’22 MS (astrophysical sciences and technology), one of Kartaltepe’s Ph.D. students. “I started working with her my freshman year and I got into multiple grad schools, but I was just so excited about what she was doing and the direction it was going, so I decided to stay here.”

Cox is working with Kartaltepe on Cosmic Evolution Early Release Science (CEERS) Survey and COSMOS, using data from JWST to study how mass was assembled in early galaxies over time. Cox said that in addition to teaching advanced concepts in astrophysics and providing opportunities to work on cutting-edge research projects, Kartaltepe takes time to teach students how to be effective collaborators and good scientists.

 “Jeyhan is very big on collaboration and communication, and really encourages people, even though we’re working remotely often across the planet, to reach out to someone,” Cox said. “I really appreciate that. She offers a lot of opportunities for her students to connect with other people and make connections, but also she’s very good at making sure we’re fully prepared to do those things.”

Astrophysical sciences and technology Ph.D. student Brittany Vanderhoof said she came to RIT specifically to study with Kartaltepe. The two met at an Astronomical Society of New York meeting in the mid-2010s while Vanderhoof was an undergraduate student at Utica College.

“I was looking for graduate schools and I wanted to study galaxy evolution and be really involved in things like supporting women and underrepresented groups in science, and Jeyhan had all of that,” said Vanderhoof. “She actually helped me with my whole graduate school process without even really knowing me and before I let her know I was interested in working with her. She was just very welcoming and helpful.”

Vanderhoof is now also a member of the COSMOS and CEERS teams, and her thesis focuses on studying how galaxy mergers can increase star formation rates. She said that ultimately she hopes that she can continue in Kartaltepe’s footsteps.

“As impressive as she seems with her dedication, research, intelligence, and the collaborations she is a part of, she is just as dedicated and caring to the people she mentors,” said Vanderhoof. “She truly cares about her people and takes care of them.”

Mobasher also noticed and admires Kartaltepe’s involvement with diversity and women’s advocacy in science. Empowering students the way Kartaltepe does, he said, is the ultimate mark of a great scientist.

“Science in general is constantly evolving, so after many years, the work we do today will be outdated and someone else will do it better,” said Mobasher. “This is the nature of science. But what remains is the impact we have on scientists and how we help people to develop their own careers. Jeyhan’s students will remember her long after they have left school.”

Kartaltepe provides her students unique opportunities to become deeply involved in projects like COSMOS-Web and CEERS. Kartaltepe, center, is pictured here with her astrophysical sciences and technology Ph.D. students Brittany Vanderhoof and Isabella Cox ’20 (physics), ’22 MS (astrophysical sciences and technology).

James web telescope

An illustration of the James Webb Space Telescope deployed in space, far left. The telescope has a large mirror made of hexagons that are being illuminated by the galaxy being observed. Otherwise, the top side of the telescope is in the dark. The underside is being lit by the sun. The telescope is set against a starry background.

What has the telescope shown so far?

The James Webb Space Telescope (JWST) has already begun to upend scientists’ previous assumptions about the universe.

The telescope was designed to observe the universe at near-infrared and mid-infrared wavelengths, which are longer than the wavelengths of visible light. That makes JWST a great tool for studying what the earliest galaxies in the universe looked like.

As light travels from a distant galaxy toward us, it is gradually stretched into longer wavelengths and shifted toward the infrared part of the spectrum. Since the universe is expanding, the most distant light from the earliest galaxies has been shifted to the longer, redder wavelengths that can only be detected through infrared. The higher the “redshift” of a galaxy, the earlier it formed.

Since JWST came online, scientists have been finding lots of examples of high redshift galaxies.

Associate Professor Jeyhan Kartaltepe is co-leading COSMOS-Web, the largest general observer program in JWST’s first year, and is a key player in other JWST programs including the Cosmic Evolution Early Release Science Survey (CEERS), Public Release Imaging for Extragalactic Research (PRIMER), and the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey. While all of these programs look at galaxy formation in the early universe, they are different in scope.

hexagonal shapes with images from the cosmos inside each

At the two ends are COSMOS-Web and NGDEEP. COSMOS-Web looks at a relatively large portion of the sky but at relatively shallow glances, albeit still much deeper than anything possible before with the Hubble Space Telescope. NGDEEP, by contrast, looks at one point in the sky and stares at it for a long time.

By analyzing data from JWST taken for the CEERS study, Kartaltepe and her collaborators have found that the structures of galaxies in the early universe were much more diverse and mature than previously known.

The team examined 850 galaxies at redshifts of z three through nine, or as they were roughly 11 billion to 13 billion years ago, using images taken by both JWST and those previously taken by the Hubble Space Telescope.

JWST’s ability to see faint, high redshift galaxies in sharper detail than Hubble allowed the team of researchers to resolve more features and see a wide mix of galaxies, including many with mature features such as disks and spheroidal components.

Out of the 850 galaxies used in the study that were previously identified by Hubble, 488 were reclassified with different structures after being shown in more detail with JWST.

Kartaltepe said COSMOS-Web will provide an even larger sample through 255 hours of observing time with the telescope.

COSMOS-Web began its observing campaign in January and will finish in January 2024, studying an area of the sky about three times the size of a full moon.

The program team released COSMOS-Web’s first images in March, but the bulk of data will become available in two batches this summer and winter.

Images of four example galaxies selected from the first epoch of COSMOS-Web NIRCam observations, highlighting the range of structures that can be seen. 1 is a barred spiral galaxy; 2 is an example of a gravitational lens, where the mass of the central galaxy is causing the light from a distant galaxy to be stretched into arcs; 3 is a nearby galaxy displaying shells of material, suggesting it merged with another galaxy in its past; 4 is a barred spiral galaxy with several clumps of active star formation.

Image credit COSMOS-Web/Kartaltepe, Casey, Franco, Larson, et al./RIT/UT Austin/CANDIDE.