Astronomers the Multi Unit Spectroscopic Explorer (MUSE) on ESO’s Very Large Telescope have observed UGC 10738, a nearby, edge-on Milky Way-like galaxy, and found that it has distinct thick and thin disks similar to those of our own Milky Way Galaxy. This suggests, contrary to previous theories, that such structures are not the result of a rare long-ago collision with a smaller galaxy; they appear to be the product of more peaceful change.
This image shows the Milky Way-like galaxy UGC 10738. Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD / PanSTARRS.
“Our observations indicate that the Milky Way’s thin and thick disks didn’t come about because of a gigantic mash-up, but a sort-of default path of galaxy formation and evolution,” said Dr. Nicholas Scott, an astronomer at the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).
“From these results we think galaxies with the Milky Way’ particular structures and properties could be described as the normal ones.”
“It was thought that the Milky Way’s thin and thick disks formed after a rare violent merger, and so probably wouldn’t be found in other spiral galaxies,” he added.
“Our research shows that’s probably wrong, and it evolved naturally without catastrophic interventions. This means Milky Way-type galaxies are probably very common.”
“It also means we can use existing very detailed observations of the Milky Way as tools to better analyze much more distant galaxies which, for obvious reasons, we can’t see as well.”
Dr. Scott and his colleagues used the MUSE instrument on ESO’s Very Large Telescope to observe UGC 10738, a spiral galaxy located some 334 million light-years away in the constellation of Ophiuchus.
They found that this galaxy, like the Milky Way, has a thick disk consisting mainly of ancient stars, identified by their low ratio of iron to hydrogen and helium, and that its thin disk stars are more recent and contain more metal.
Although such disks have been previously observed in other galaxies, it was impossible to tell whether they hosted the same type of star distribution — and therefore similar origins.
“Using MUSE, we were able to assess the metal ratios of the stars in its thick and thin disks,” said Dr. Jesse van de Sande, also from the University of Sydney and ASTRO 3D.
“They were pretty much the same as those in the Milky Way — ancient stars in the thick disk, younger stars in the thin one.”
“We’re looking at some other galaxies to make sure, but that’s pretty strong evidence that the two galaxies evolved in the same way.”
“This is an important step forward in understanding how disk galaxies assembled long ago,” said Professor Ken Freeman, an astronomer at the Australian National University.
“We know a lot about how the Milky Way formed, but there was always the worry that the Milky Way is not a typical spiral galaxy.”
“Now we can see that the Milky Way’s formation is fairly typical of how other disk galaxies were assembled.”
“This work shows how the Milky Way fits into the much bigger puzzle of how spiral galaxies formed across 13 billion years of cosmic time,” said Professor Lisa Kewley, director of ASTRO 3D.
The findings were published in the Astrophysical Journal Letters.
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Nicholas Scott et al. 2021. Identification of an [α/Fe]-Enhanced Thick Disk Component in an Edge-on Milky Way Analog. ApJL 913, L11; doi: 10.3847/2041-8213/abfc57
