Case Western Reserve University undergraduate student Chris Carr and colleagues have spotted a very diffuse extragalactic cloud in a group of galaxies in the constellation Leo.
Wide field image of the Leo I galaxy group. BST1047+1156 is located at the center of the white box. Image credit: Mihos et al, doi: 10.3847/2041-8213/aad62e.
The newly-discovered object, BST1047+1156, is part of a collection of about 24 galaxies called the Leo I group (also known as the M96 group).
“It was so faint he hardly saw it. But I flagged it for Case Western Reserve University’s Professor Chris Mihos, with whom I’d been working the past two weeks, and explored the coordinates further,” Carr said.
“What we found pointed to the detection of a new galaxy about 37 million light-years away.”
BST1047+1156 has a radius of about 6,500 light-years and is approximately 3 billion years old.
The object has two tidal tails and is found embedded within diffuse gas connecting the spiral galaxy Messier 96 (also known as M96 or NGC 3368) to the Leo I group’s extended gas ring.
“I wasn’t quite sure how to feel,” Carr said of the discovery. “It’s not really something you are prepared for, especially this early.”
“As we learned more about this bizarre smudge in our images, the significance of the discovery really began to come into focus, and that’s when it sunk in that this was something truly special.”
While its origins remain unclear, Carr and co-authors stated it is the ‘lowest surface brightness object ever detected via integrated light.’
“The nature of BST1047+1156 is unclear,” the astronomers said.
“It could be a disrupting tidal dwarf, recently spawned from star formation triggered in the Leo I group’s tidal debris.”
“Alternatively, the object may have been a pre-existing galaxy — the most extreme example of a gas-rich field low surface brightness galaxy known to date — which had a recent burst of star formation triggered by encounters in the group environment.”
The discovery is reported August 6 in the Astrophysical Journal Letters (arXiv.org preprint).
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J. Christopher Mihos et al. 2018. BST1047+1156: An Extremely Diffuse and Gas-rich Object in the Leo I Group. ApJL 863, L7; doi: 10.3847/2041-8213/aad62e
