Donatiello I, also known as Mirach's Goblin, is a dwarf spheroidal galaxy in the constellation Andromeda, located between 8.1 and 11.4 million light-years from Earth. It is a possible satellite galaxy of the dwarf lenticular galaxy NGC 404, "Mirach's Ghost", which is situated 60 arcminutes away. It is otherwise one of the most isolated dwarf spheroidal galaxies known, being separated from NGC 404 by around 211,000 light-years. The galaxy is named after its discoverer, amateur astronomer and astrophotographer Giuseppe Donatiello, who sighted the galaxy in a 2016 review of his archival long exposures from 2010 and 2013. Follow-up observations with the Roque de los Muchachos Observatory led to a scientific paper on its discovery being published in December 2018.
Quick Facts Observation data (J2000 epoch), Constellation ...
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Donatiello I is named after its discoverer, Italian amateur astronomer and astrophotographer Giuseppe Donatiello,[2][3] and is abbreviated to "Do I".[4] The galaxy's nickname, "Mirach's Goblin", is a reference to the nearby dwarf lenticular galaxy NGC 404, with which it may be physically associated.[5] NGC 404 is nicknamed "Mirach's Ghost" due to its proximity to the second magnitude star Mirach.[5][6]
Donatiello I is a dwarf spheroidal galaxy at an estimated distance from Earth between 2.5 and 3.5 megaparsecs, or 8.1 and 11.4 million light-years,[7][8] outside the Local Group.[7][8] Its luminosity is around 200,000 times greater than that of the Sun, with an absolute magnitude of around −8.3 and a surface brightness of 26 magnitudes per negative square arcsecond.[9] Its effective radius is roughly estimated to be 400 parsecs, while its ellipticity is around 0.7.[10] Donatiello I is one of the most isolated dwarf spheroidals known,[11][12] and is a possible satellite galaxy of its nearest neighbor, NGC 404,[5] which is located around 65 kiloparsecs away from it, or 211,000 light-years.[lower-alpha 2][13] Donatiello I could have either been involved in, or affected by, a possible merger between NGC 404 and an irregular dwarf galaxy around 900 million years ago.[14][15] Like similar dwarf spheroidal galaxies orbiting the Milky Way Galaxy and Andromeda Galaxy, Donatiello I is populated with metal-poor red dwarfs, with no active star formation occurring.[8][16]
Location of Donatiello I in the constellation
Andromeda (circled)
Donatiello I lies in the constellation Andromeda, at a right ascension of 01h 11m 40.37s and declination of +34° 36′ 3.2″, in the J2000 epoch.[17][18] In the galactic coordinate system, it is located at a longitude of 127.65° and a latitude of −28.08°.[17] It is situated 60 arcminutes away from Mirach, and 72.4 arcminutes away from NGC 404.[4] Its apparent diameter is roughly 60 arcseconds,[lower-alpha 3] while its surface brightness is around 27 magnitudes per square arcsecond.[19][20] Amateur astronomer and astrophotographer Giuseppe Donatiello first sighted the galaxy in 2016 while surveying an archived 6000-second exposure of an area around the Andromeda Galaxy taken on 5–7 November 2010 and 5 October 2013 in the Pollino National Park, with a custom-built 12.7 centimetre telescope.[21][22][23] Donatiello intended to capture stellar streams and dwarf galaxies around Andromeda that had been reported at the time.[22][24]
The discovery was corroborated using images from the Sloan Digital Sky Survey's ninth data release, which showed a faint object in the same area,[18][24] and was announced by Donatiello on 23 September 2016, via a post on Facebook.[18][24] Donatiello collaborated with a team led by David Martínez-Delgado of Heidelberg University, after Delgado had come across Donatiello's post,[25][26] to make further observations of the galaxy with the Roque de los Muchachos Observatory's Galileo National Telescope and Gran Telescopio Canarias in La Palma, Spain, on 27 November 2016.[26][23] The team's scientific paper on the discovery and their follow-up observations was submitted to the journal Astronomy & Astrophysics in April 2018, and was accepted and published in December 2018,[27] with a preprint released on arXiv in October.[25] Further detailed observations with the Hubble Space Telescope have been suggested by the paper's authors as a way to better determine the galaxy's distance from Earth and its relationship with NGC 404,[28] along with Donatiello I's size and mass.[29]
Notes
Photograph taken with the Device Optimized for the Low Resolution (DOLoRes) instrument on the Galileo National Telescope, using 35 exposures lasting 180 seconds each, with two different optical filters, on 27 November 2016.[1] Surmised from NGC 404's tip of the red-giant branch (TRGB) distance from Earth, which is 3.1 megaparsecs, Donatiello I and NGC 404 are separated by 65 kiloparsecs.[7] Surmised from its apparent radius of 0′.48 ± 0.15, Donatiello I's apparent diameter from Earth is 0′.96 ± 0.30, which is equal to 57.6±18 seconds of arc.[10]
Sources
- Berke, Daniel (22 November 2018). "Mirach's Ghost and Mirach's Goblin: A New Galaxy Found Near the Local Group". Astrobites. Archived from the original on 21 February 2019. Retrieved 21 February 2019.
- Crockett, Christopher (24 October 2018). "Dwarf Galaxy Found by Amateur". Sky & Telescope. Archived from the original on 22 February 2019. Retrieved 22 February 2019.
- Instituto de Astrofísica de Canarias (23 November 2018). "An amateur astronomer discovers a dwarf galaxy". Instituto de Astrofísica de Canarias. Archived from the original on 21 February 2019. Retrieved 21 February 2019.
- Martínez-Delgado, David; Grebel, Eva K.; Javanmardi, Behnam; Boschin, Walter; Longeard, Nicolas; Carballo-Bello, Julio A.; Makarov, Dmitry; Beasley, Michael A.; Donatiello, Giuseppe; Haynes, Martha P.; Forbes, Duncan A.; Romanowsky, Aaron J. (6 December 2018). "Mirach's Goblin: Discovery of a dwarf spheroidal galaxy behind the Andromeda galaxy". Astronomy & Astrophysics. 620: A126. arXiv:1810.04741. Bibcode:2018A&A...620A.126M. doi:10.1051/0004-6361/201833302. S2CID 55255865.
Citations
Martínez-Delgado et al. 2018, "...obtained with the instrument Device Optimized for the Low Resolution (DOLoRes) of the 3.58-m Italian Telescopio Nazionale Galileo (TNG) (Roque de Los Muchachos Observatory, LaPalma, Spain) taken on November 27, 2016. These observations include 20x180-sec exposures in the g′-band and 15×180 sec exposures in the r’-band..." Berke 2018, "As a recognition of his discovery, the galaxy was named "Donatiello 1."" Martínez-Delgado et al. 2018, "We have reported the discovery of Do I, a faint stellar system at a projected distance of one degree from the Mirach (βAnd) star. [...] Do I lies 72.4 arcmin on the sky from NGC 404, which corresponds to a projected separation of 65 kpc if we adopt the TRGB distance of NGC 404 equal to 3.1 Mpc." Instituto de Astrofísica de Canarias 2018, "The position and the distance of Donatiello 1 suggest that it is a dwarf satellite of the nearby elliptical galaxy known [as] "The Ghost of Mirach" because it is close to the star Mirach." Berke 2018, "Its diffuse, nebulous look could easily be mistaken for a blurry internal reflection of Mirach in those early telescopes, which led to its common nickname of "Mirach’s Ghost."" Martínez-Delgado et al. 2018, "...observations obtained with the Gran Telescopio Canarias (La Palma, Spain) reveals that this system is beyond the Local Group [...] Our data suggest a distance range of 2.5–3.5 Mpc for Do I, and its structural parameters and absence of HI are consistent with those of a dwarf spheroidal galaxy, similar to the known companions of the Milky Way or M31." Berke 2018, "It appears to be a dwarf spheroidal galaxy that is no longer actively forming stars, similar to many of the small galaxies orbiting the Milky Way and the Andromeda Galaxy within the Local Group. [...] they were able to constrain it to within about 8.1 to 11.4 million light-years away. This places it comfortably beyond the Local Group..." Martínez-Delgado et al. 2018, "Table 1. Properties of the Donatiello I dwarf galaxy [...] MV −8.3+0.3
−0.3; LV 105.3+0.2
−0.3 L☉; μV (mag arcsec−2) 26.5±1.0" Martínez-Delgado et al. 2018, "Table 1. Properties of the Donatiello I dwarf galaxy [...] Ellipticity 0.69±0.05; rh 0′.48 ± 0.15 - 442±157 pc" Martínez-Delgado et al. 2018, "In the case of a distance for Do I of 2.5 Mpc, it would be one of the most isolated dSph galaxies reported so far." Berke 2018, "If it lies around 10 million light-years away from the Milky Way it would likely be only about 211,000 light-years away from NGC 404, and possibly associated with it." Martínez-Delgado et al. 2018, "...del Rio et al. (2004) argued that this gaseous ring around NGC 404 is the remnant of a merger with a dwarf irregular galaxy which took place some 900 Myr ago. The proximity of Do I and its elongated shape lead one to speculate that it might have been involved in that interaction or potentially have been affected by it." Berke 2018, "Interestingly, there is some evidence that NGC 404 has undergone a collision or interaction fairly recently [...] Donatiello 1 is also noticeably elongated and non-spheroidal, suggesting a possible recent interaction with NGC 404..." Martínez-Delgado et al. 2018, "The main feature of the diagram is the red giant branch (RGB) locus, suggesting that the stellar population of this dwarf galaxy is dominated by old, metal-poor stars similar to those observed in dSph galaxies in the Local Group." Martínez-Delgado et al. 2018, "Table 1. Properties of the Donatiello I dwarf galaxy; α (J2000) 01h 11m 40.37s; δ (J2000) +34° 36′ 3.2″; l 127.65°; b −28.08°" Crockett 2018, "Martínez-Delgado came across the discovery on Facebook. Donatiello had posted his discovery image to the site, after convincing himself that the galaxy was the real deal when he noticed a similar smudge at the same coordinates (RA 01h 11m 40.37s, dec. +34° 36' 3.2") in images from the Sloan Digital Sky Survey." Crockett 2018, "The dwarf galaxy is faint, too. With a surface brightness of just 26.5 magnitudes per square arcsecond, it's barely visible against the sky." Martínez-Delgado et al. 2018, "Discovery image of Donatiello I dwarf galaxy [...] from the Pollino National Park in Southern Italy. The total exposure time is about 6000 seconds obtained by combining (sum and median) images captured on 5,6,7 November 2010 and 5 October 2013 with the same equipment." Crockett 2018, "From the dark skies of Pollino National Park in southern Italy, Giuseppe Donatiello had been investigating the Andromeda Galaxy with his home-built telescope, looking for previously reported dwarf galaxies and stellar streams." Williams, Matt (26 October 2018). "Has a New Dwarf Galaxy Been Found Hiding Behind Andromeda?". Universe Today. Archived from the original on 22 February 2019. Retrieved 22 February 2019. Using a 12.7-cm telescope, Donatiello captured a mosaic of deep images of the Andromeda galaxy [...] follow-up observations made on Nov. 27th, 2016. These were performing using the 3.58 meter Telescopio Nazionale Galileo (TNG) and the 10.4 meter Gran Telescopio Canarias (GTC), both of which are located at the IAC's Roque de Los Muchachos Observatory on the island of La Palma, Spain.
Martínez-Delgado et al. 2018, "Donatiello I (Do I) was first found on 23 September 2016 in a visual inspection of a deep amateur image of the Andromeda galaxy region [...] The main purpose of this wide-field mosaic of the area [...] was to detect the stellar streams and M31 satellites previously reported in the PAndAs [...] The detection was confirmed by a visual inspection of the SDSS DR9 images..." Crockett 2018, "David Martínez-Delgado (Heidelberg University, Germany), lead author on the paper reporting the discovery, published October 10th on the astronomy preprint arXiv. [...] Martínez-Delgado reached out and offered to collaborate on a paper." Berke 2018, "...David Martinez-Delgado, discovered the image after Donatiello posted it on Facebook, and reached out to him to help secure time on professional telescopes for follow-up and make sure he received proper credit for his discovery. [...] They were able to take observations with both the 3.58-meter Italian Telescopio Nazionale Galileo (TNG) and the 10.4-m Gran Telescopio Canarias (GTC), both part of the Roque de Los Muchachos Observatory on the Spanish islands of La Palma." Martínez-Delgado et al. 2018, "Because of its distance range and its crowding level, deeper, high resolution Hubble Space Telescope imaging and radial velocity observations are needed to constrain the distance of Do I and definitively determine if it is a NGC 404 companion. Crockett 2018, "Martínez-Delgado and colleagues hope to get a better look at this galaxy with the Hubble Space Telescope. That should allow them to nail down the distance, which in turn would provide more precise estimates of other properties such as size and mass."
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