The Magellanic Clouds are two of our closest neighbors in galactic terms. The pair of irregular dwarf galaxies were dragged into orbit the Milky Way in the distant past, and we have viewed them since the dawn of mankind. Some of our ancestors even collected pigments and created images of them in petroglyphs and cave paintings.
Following in the footsteps of these ancient artists, astronomers recently used the Dark Energy Camera (DECam) to capture a detailed portrait of the pair of galaxies.
The Magellanic Clouds are not visible to residents of the Northern Hemisphere, but they are quite noticeable in the Southern Hemisphere. Observers sometimes say they look like pieces of the Milky Way galaxy that have separated. But it's the other way around: they are separate structures that were born that know where and they are slowly being drawn into our galaxy and consumed, starting with their gas halos.
The pair of galaxies has been observed many times at depth. But this new effort has produced the most detailed picture of them ever. It's all part of an effort to better understand how these two companions were formed. The observations of the clouds contain about 4 million measurements from 360 million objects.
Credit: Image Processing: Travis Rector (University of Alaska Anchorage), Mahdi Zamani & Davide de Martin
The Dark Energy Camera is located on the 4-meter Víctor M. Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. The DECam is a 520 megapixel high-performance camera that has been in operation since 2012. It was mainly developed as part of the Dark Energy Survey, but also performs other scientific observations.
In this latest data release, DECam's performance was focused on the Magellanic Clouds, resulting in the deepest data set of the two satellite galaxies to date. All of this is part of the so-called SMASH survey or the survey on the history of the MAgellanic Stellar.
"To date, this is the deepest and most extensive astronomical data set of the Magellanic Clouds that are closest to us," explains David Nidever, assistant professor at the Physics Institute at Montana State University and principal investigator of the SMASH survey. "These satellite galaxies have been studied for decades, but SMASH is being used to fully map their structure and solve the mystery of their formation."
Because the Magellanic Clouds are so close to us, they offer a great opportunity to study small galaxies and understand how they formed. In a 2017 article announcing the first data release from SMASH, the authors wrote, “The Large and Small Magellanic Clouds (LMC and SMC) are unique as two of the closest and most massive satellite galaxies in the Milky Way (MW) Opportunity to study in detail the processes of galaxy formation and evolution of low mass galaxies. The clouds have long been of great importance to astronomy, both as laboratories for astrophysical processes and as calibrators of the extragalactic distance scale. As the best example of an interacting pair of galaxies, they offer a special insight into the effects of such interactions on the structure and evolution of galaxies. "
But their proximity is both helpful and challenging. The universe contains a huge population of dwarf galaxies, and most of them are at extreme distances and appear only as tiny, dark objects. Compare that to the LMC and SMC which can be seen with the naked eye. Unfortunately, this also means that it is difficult to map them completely and in detail. But DECam and SMASH are up to the task.
DECam in operation while an observer watches from a chair. Photo credit: The Dark Energy Survey
Overall, SMASH covered an area of the sky 2,400 times larger than the full moon, although more than 50 nights of observations were required. The central regions of each cloud are the most complex, and this second data release includes new observations from both regions.
The Magellanic Clouds are unusual in that they are still rapidly forming new stars. They have pretty large populations of young stars. SMASH's deep and detailed dataset allows astronomers to study their star populations in more detail to look for clues to their history. They found evidence that the two clouds collided in the past and that the collision sparked the episode of intense star formation.
“These are beautiful multicolored images of the closest neighboring galaxies to the Milky Way. With the care that the dedicated team has shown, they give us a remarkable insight into the thirteen billion year history of star formation in these galaxies, ”explains Glen Langston, Program Manager at the National Science Foundation.
A press release announcing SMASH's second data release outlines three scientific goals:
Use star formation data to create a movie about how galaxies evolved over time. Involve citizen scientists on the search for star clusters in both galaxies. Measure the metallicity of stars in the clouds.
"These latest SMASH data of the central regions of the Magellanic Clouds, in which most of the stars are located, are unique in their combined depth, latitude and uniformity," explains Knut Olsen, NOIRLab scientist and co-leader of the survey. “With this data we can not only produce amazing images, but also look into the past and reconstruct how the Magellanic Clouds formed their stars over time. With these "films" of star formation, we can try to understand how and why these galaxies evolved. "
The data publication is featured in a new article published in the Astronomical Journal. The title is "The second data release of the survey on the history of the MAgellanic Stellar".