A new image taken with NASA/ESA Hubble Space Telescope shows Donatiello II, a recently-discovered dwarf galaxy associated with the nearby spiral galaxy NGC 253.
This Hubble image shows Donatiello II (center), an ultra-faint dwarf galaxy some 11.4 million light-years away in the constellation of Sculptor. Image credit: NASA / ESA / Hubble / B. Mutlu-Pakdil / G. Donatiello.
Donatiello II is located approximately 11.4 million light-years away in the constellation of Sculptor.
Also known as Scl-MM-dw3, this dwarf galaxy is only 724 light-years across.
“If you cannot quite distinguish the clump of faint stars that is all we can see of Donatiello II in this image, then you are in good company,” Hubble astronomers said.
“Donatiello II is one of three newly discovered galaxies (the other two are Donatiello III and Donatiello IV) that were so difficult to spot that they were all missed by an algorithm designed to search astronomical data for potential galaxy candidates.”
“Even the best algorithms have their limitations when it comes to distinguishing very faint galaxies from individual stars and background noise.”
“In these most challenging identification cases, discovery has to be done the old-fashioned way — by a dedicated human trawling through the data themselves.”
The initial data that enabled the discovery of Donatiello II, Donatiello III and Donatiello IV were collected by the Dark Energy Survey (DES), an intense observation effort that was carried out using the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory.
“As is the case for most major telescopes that receive public funding, the DES data were made available to the public,” the astronomers said.
“That is when the experienced amateur astronomer Giuseppe Donatiello stepped in.”
“He laboriously processed and analyzed chunks of the DES data, and made his discovery of three ultra-faint dwarf galaxies.”
“All three are satellites of the well known Sculptor galaxy (otherwise known as NGC 253), meaning that they are all bound gravitationally to their much more massive companion.”
Based on their own independent search, University of Chicago astrophysicist Burçin Mutlu-Pakdil and colleagues used Hubble’s Advanced Camera for Surveys (ACS) to obtain long-exposure images of several faint galaxies, including Donatiello II.
“With the Hubble images, they were able to confirm their target galaxies’ association with NGC 253 — thereby providing both an independent confirmation of Donatiello’s discovery,” the researchers said.
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Burçin Mutlu-Pakdil et al. 2022. Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-faint Dwarf Galaxies. ApJ 926, 77; doi: 10.3847/1538-4357/ac4418
