Discovery of a new ultra-faint dwarf galaxy

Discovery of a new ultra-faint dwarf galaxy

Discovery of a new ultra-faint dwarf galaxy

Tucana B as seen in the DESI Legacy Imaging Surveys sky navigator (left) and in deeper r-band IMACS data from Magellan (right), where it is more clearly resolved into stars. Credit: Sand et al., 2022.

Astronomers from the University of Arizona (UA) and elsewhere report the discovery of a new ultra-faint dwarf galaxy. The new galaxy, designated Tucana B, is the first extinct and isolated object of its type identified in the extreme periphery of the local group. The discovery is reported in an article published on May 18 on the arXiv preprint server.

Ultra-faint dwarf (UFD) galaxies are the faintest, most dark matter-dominated, and least chemically evolved galaxies known. Therefore, they are seen by astronomers as the best fossil candidates for the early universe.

Now, a team of researchers led by UA’s David J. Sand has found a new UFD during a visual search for faint dwarf galaxies companions to the distant dwarf spheroid galaxy Tucana. They used data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and their interactive color image viewer.

“We uploaded a custom file to delineate a region with a projected radius of 100 kpc (≈6.4 degrees at the Tucana distance) and searched for visual overdensities of resolved stars with underlying diffuse light, indicating a dwarf galaxy at the edge of the local group. The field was inspected at a variety of spatial scales and contrast levels. Tucana B stood out during the search and is partially resolved into stars in the Legacy Imaging Survey viewer,” wrote explained the astronomers.

According to the article, Tucana B is located about 6 degrees from the Tucana dwarf spheroid and is about 1.6 million light-years farther along the line of sight. The distance between Tucana B and Earth has been calculated to be around 4.5 million light-years.

Tucana B has a half-light radius of about 260 light-years and an absolute magnitude of −6.9 mag, making it comparable to the ultra-faint satellite galaxies of the Milky Way. The UFD appears to consist of only an ancient, metal-poor stellar population.

Astronomers noted that Tucana B’s brightness and apparent lack of star formation and neutral gas make it unique among recent discoveries at this approximate distance. Additionally, Tucana B’s extreme isolation may indicate that its star formation was quenched by reionization or some other internal mechanism, rather than by interaction with a larger galaxy halo.

Sand’s team sees Tucana B as an excellent target for future space-tracking observations aimed at determining its structure and star-forming history, possibly back to the oldest main-sequence intersection.

“In particular, Tucana B may provide a definitive opportunity to understand the role that reionization plays in the extinction of fainter galaxies,” the researchers concluded.

They added that finding more objects like Tucana B is necessary in order to better understand the demographics of the UFD population in the field.

Astronomers detect extended dark matter halo around ancient dwarf galaxy

More information:
DJ Sand et al, Tucana B: An isolated, extinct ultra-faint dwarf galaxy at D=1.4 Mpc. arXiv:2205.09129v1 [astro-ph.GA]

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Quote: New Ultra-Faint Dwarf Galaxy Discovered (2022, May 26) Retrieved May 27, 2022 from

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