DGSAT I | |
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Observation data | |
Right ascension | 01h 17m 35.59s [1] |
Declination | 33° 31′ 42″ [1] |
Redshift | 78 Mpc [1] |
Heliocentric radial velocity | 5450 ± 40 km/s [1] |
Distance | 254.4 ± 3.3 Mly (78 ± 1 Mpc) [1] |
Apparent magnitude (V) | 18.18 ± 0.04 [1] |
Absolute magnitude (V) | -16.3 ± 0.1 mag [1] |
Characteristics | |
Mass | 4.0 × 10×108 [1] M☉ |
Mass/Light ratio | 1.1 [1] M☉/L☉ |
DGSAT I is a quenched, ultra diffuse galaxy (UDG) located on the outskirts of the Pisces-Perseus Supercluster, identified in 2016 during a visual inspection of a full color image of the Andromeda II dwarf galaxy. [1] DGSAT I resides in a low-density environment compared to the densities where UDGs are typically found. [2] Its chemical makeup have led astronomers to propose it was formed during the dawn of the universe when galaxies emerged in a different environment than today. [3] [4] [5] [6]
DGSAT I was first identified by the DGSAT project in 2016. [7] The DGSAT (Dwarf Galaxy Survey with Amateur Telescopes) uses the potential of privately owned small-sized telescopes to probe low surface brightness (LSB) features around large galaxies and aims to increase the sample size of the dwarf satellite galaxies in the Local Volume. [7] [8]
At first astronomers thought DGSAT I to be an isolated dwarf galaxy beyond the Local Group due to its structural properties and absence of emission lines. A spectroscopic observation later revealed DGSAT I to be a background system and likely associated with an outer filament of the Pisces-Perseus super-cluster. [7]
The chemical composition of a galaxy provides record of the ambient conditions during its formation. The mass ratios of alpha-elements such as magnesium to iron ([Mg/Fe]) trace time-scales for star formation, as these elements are produced by stars according to different lifetimes. [2] Younger galaxies tend to have more heavy elements in its chemical makeup compared to ancient galaxies formed during an early age of the universe. [3]
DGSAT I's integral field spectroscopy data shows a remarkably low iron content, suggesting an early galaxy formed from a nearly pristine gas cloud, unpolluted by the supernova death of previous stars, however its magnesium levels are consistent with what astronomers expect to find in younger galaxies. [3] This apparent chemical makeup discrepancy and DGSAT I's isolation from galaxy clusters are helping astronomers to develop new theories concerning the birth and formation of UDGs. [3]
UDGs are hard to observe due to their extremely low luminosity but there are studies being conducted using the Keck Cosmic Web Imager in an attempt to shed light on the precise relation between DGSAT I's metallicity and its possibly exotic origin. [2] A paper published in 2022 proposed DGSAT I to be a “failed galaxy” that formed relatively few stars in proportion to its halo mass, and could be related to cluster UDGs whose size and quiescence pre-date their infall [9] (i.e. when molecular transition shows evidence of gas flowing into the core of the star).
The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10 6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.
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A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.
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NGC 4449, also known as Caldwell 21, is an irregular Magellanic type galaxy in the constellation Canes Venatici, being located about 13 million light-years away. It is part of the M94 Group or Canes Venatici I Group that is relatively close to the Local Group hosting our Milky Way galaxy.
The Pavo–Indus Supercluster is a neighboring supercluster located about 60–70 Mpc (196–228 Mly) away in the constellations of Pavo, Indus, and Telescopium. The supercluster contains three main clusters, Abell 3656, Abell 3698, and Abell 3742.
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Robert Jay GaBany is an American amateur astronomer and astrophotographer who is also known for his work with an international team of astrophysicists led by Dr. David Martínez-Delgado. GaBany helped pioneer the use of modest size telescopes and off the shelf CCD-cameras to produce long exposure images that revealed ancient galactic merger remnants in the form of star streams surrounding nearby galaxies that were previously undetected or suspected.
An ultra diffuse galaxy (UDG), or Dark galaxy, is an extremely low luminosity galaxy, the first example of which was discovered in the nearby Virgo Cluster by Allan Sandage and Bruno Binggeli in 1984. These galaxies have been studied for many years prior to their renaming in 2015. Their lack of luminosity is due to the lack of star-forming gas, which results in these galaxies being reservoirs of very old stellar populations.
Dragonfly 44 is an ultra diffuse galaxy in the Coma Cluster. This galaxy is well-known because observations of the velocity dispersion in 2016 suggested a mass of about one trillion solar masses, about the same as the Milky Way. This mass was consistent with a count of about 90 and 70 globular clusters observed around Dragonfly 44 in two different studies.
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