New, improved Dragonfly telescope is a galactic gas detector

This image zooms in on a newly forming tidal dwarf galaxy, which appears like a
This image zooms in on a newly forming tidal dwarf galaxy, which appears like a clump of gas at the edge of the disk of the M82 galaxy. Red regions are emissions from ionized gas. (Courtesy of the Dragonfly telescope team)

The Dragonfly telescope is undergoing a metamorphosis.

For the past decade, the Dragonfly Telephoto Array - designed by Yale’s Pieter van Dokkum and the University of Toronto’s Roberto Abraham and located in New Mexico - has conducted groundbreaking science by detecting faint starlight within dimly lit parts of the night sky. The telescope uses clusters of telephoto lenses to create images, much the way a dragonfly’s eyes gather visual data.

The telescope has spotted previously unseen "fluffy" galaxies , diffuse dwarf galaxies , and galaxies with little or no dark matter.

Now Dragonfly is setting its sights on extragalactic gas.

With the help of a special filter mounted in front of each lens, the Dragonfly telescope is able to block most of the light emitted by stars - leaving just the faint glow of light-emitting, ionized gas. The Dragonfly team built a "pathfinder" version of the new telescope, with three lenses instead of the original Dragonfly’s 48 lenses, as a proof-of-concept device.

The results are even better than expected, the researchers say.

" There are going to be some incredible images from Dragonfly in the next few years," said van Dokkum, the Sol Goldman Family Professor of Astronomy in Yale’s Faculty of Arts and Sciences. "This new method of detecting gas clouds is opening up a whole new regime of science to explore."

In a pair of new studies, the Dragonfly team describes previously hidden features within the gas surrounding a group of galaxies located about 12 million light-years from Earth. The researchers chose this area, in part, because it has been studied by other telescopes and provides a number of established, celestial signposts to gauge Dragonfly’s accuracy.

" The Messier 81 galaxy group is one of the nearest to our own, making it one of the best to study," said Yale graduate student Imad Pasha, first author of one of the new studies. "We’re returning to many such well-known, nearby galaxies with this new instrument to add pieces to the puzzle of how gas gets in and out of galaxies."

Although it has long been known that gas is the fuel for creating stars and planets in galaxies, the dynamics for how this gas actually gets into and out of galaxies are not well understood. Being able to isolate images of gas structures around galaxies has become a priority for researchers.

For example, Pasha’s study, published in Astrophysical Journal Letters , describes a nascent dwarf galaxy forming in a tidal arm of the galaxy Messier 82. Essentially, a new galaxy is being formed by the gas ripped away from M82 when M82 flew past its neighbor, M81.

" This type of galaxy is difficult to detect by traditional observations," Pasha said. "We may well find more of these ’baby’ galaxies around well-studied groups in the future."

The second new study, which has been accepted by the Astrophysical Journal, describes a giant cloud of ionized gas - 180,000 light years long and 30,000 light years wide. Although the cloud’s origin remains a mystery, the researchers theorize that it may have been pulled away from M82 during a close encounter with its larger, companion galaxy, Messier 81, or blown away from M82 by strong "superwinds."

" This cloud had never been seen before," said first author Deborah Lokhorst, a former graduate student at the University of Toronto. "Our image was the first with the sensitivity required and a wide enough field of view to detect it. We almost didn’t believe it was real!"

Now that the Dragonfly "pathfinder" has proven to be successful, the researchers are building a bigger Dragonfly Spectral Line Mapper instrument with 120 lenses. The telescope is being assembled over the next year in New Mexico.

Co-author Seery Chen, a University of Toronto graduate student who worked on instrumentation development for the new Dragonfly, said part of the project’s ethos is to conduct groundbreaking science using readily available materials - including commercially available telephoto lenses. Eventually, the team plans to make all of its instrument designs and data open-sourced and available to other researchers.

" It makes science more accessible to more people," Chen said.

Co-authors of the new studies include Yale graduate students Tim Miller, Erin Lippitt, Ava Polzin, Zili Shen, and Michael Keim, and former Yale researchers Shany Danieli, now at Princeton, and Allison Merritt, now at the Max-Planck-Institut für Astronomie in Germany.

Jim Shelton