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Small dwarf galaxy identified as the source of the outer disk of galaxy M64 upon closer examination.


Bottom center: a gri-color mosaic of observations taken with a Subaru HSC in the deepest of the three fields, field 3. M64 is visible at the top of the field, which is ∼115 kpc at its widest, with much diffuse brightness associated with subtracted disc as part of the reduction . Galactic noise can be seen as filamentous features scattered over much of the field, the color of which complicates inferences to M64’s stellar halo from the merged light. Notes are displayed with a logarithmic span. Bottom insets: 3 × 3 magnified regions in M64’s halo, viewed in the same extension as the larger image, showing examples of regions dominated by stars resolved in the distance of M64 (left, blue) and background galaxies (right, green). Top right: HST color image of the interior of M64 from the Hubble Heritage Project. The M64’s dusty inner disc, from which its “evil eye” nickname is derived, is prominent. Top left: H i Moment 1 velocity map, taken from the THINGS survey (Walter et al. 2008). Two gas disks can be seen in M64, with the larger outer disk rotating the inner disk and the larger part of M64’s stars. credit: arXiv (2023). doi: 10.48550/arxiv.2305.17135

An international team of astronomers, astrophysicists and cosmologists has found evidence of the outer disk of galaxy M64 originating from a smaller nearby dwarf galaxy. The team wrote a paper describing their findings which has been accepted for publication in Astrophysical Journal Letters– In the meantime, it can be read on arXiv Prepress server.

Astronomers have known about the existence of M64 for two and a half centuries – and it’s notorious for its ominous appearance, which gave rise to its nickname. evil eye Previous study of the galaxy showed that it is unique in that its inner parts rotate in the opposite direction to its outer parts.

This has led to speculation that the outer fragment was cannibalized from another nearby dwarf galaxy. However, previous work could not find any evidence of the previous existence of the other galaxy. In this new effort, researchers have finally found what others have been looking for–material near M64 left over from another, smaller galaxy when it was disintegrated.

To learn more about M64, the researchers studied data from the Subaru Telescope’s Hyper Suprime-Cam, looking at regions around the galaxy rather than directly at it. In doing so, they found evidence of a galactic halo – which is known to form during galaxy mergers.

They also found a dense cluster of stars known as a shell – such formations also arise during galaxy mergers; Gravitational interactions push them together. The team then created shell imaging simulations and showed that they lined up with previous findings with other small galaxy mergers – where a smaller galaxy is pulled into a larger galaxy.

The team then confirmed what they observed by studying data from Hubble. It allowed them to make estimates regarding the composition and mass of the galaxy they suspected of being absorbed.

They found that both are similar to the Small Magellanic Cloud, a small nearby galaxy to the Milky Way — previous research has shown it to be slowly being pulled apart. The density has been found to be about 500 million solar masses, which is roughly equivalent to the mass of the hydrogen disk that makes up the outer part of galaxy M64.

The researchers conclude that their work together provides a strong case for cannibalizing a dwarf galaxy as the source of M64’s outer hydrogen disk.

more information:
Adam Smyrsina et al., Origins of the Evil Eye: Stellar Halo M64 Reveals Recent Accretion of an SMC Cluster Satellite, arXiv (2023). doi: 10.48550/arxiv.2305.17135

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the quote: A closer look at the outer disk of galaxy M64 shows that it came from a smaller dwarf galaxy (2023, May 30) Retrieved on May 30, 2023 from https://phys.org/news/2023-05-closer-galaxy-m64- outer -disk. html

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