NGC 1232 | |
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![]() NGC 1232 by ESO | |
Observation data (J2000 epoch) | |
Constellation | Eridanus |
Right ascension | 03h 09m 45.5s [1] |
Declination | −20° 34′ 46″ [1] |
Redshift | 0.005347 [1] |
Heliocentric radial velocity | 1603 ± 1 km/s [1] |
Distance | 61 ± 8.5 Mly (18.7 ± 2.6 Mpc) [2] |
Apparent magnitude (V) | 10.9 [1] |
Characteristics | |
Type | SAB(rs)c [1] |
Apparent size (V) | 7′.4 × 6′.5 [1] |
Notable features | Discrepant galaxy pair with NGC 1232 A |
Other designations | |
PGC 11819, [1] Arp 41 [1] |
NGC 1232, also known as the Eye of God Galaxy is an intermediate spiral galaxy about 60 million light-years away [2] in the constellation Eridanus. It was discovered by German-British astronomer William Herschel on 20 October 1784. [3]
It is dominated by millions of bright stars and dark dust, in spiral arms rotating about the center. Open clusters containing bright blue stars are sprinkled along these spiral arms, with dark lanes of dense interstellar dust between. Less visible are dimmer stars and interstellar gas, comprising such a high mass that they dominate the dynamics of the inner galaxy. Not visible is matter of unknown form called dark matter, needed to explain the motions of the visible material in the outer galaxy. The galaxy is approximately 200,000 light-years across. The galaxy's spiral arms are not smooth and perturbed, leading to some suggesting a collision with a dwarf galaxy. [4] [5] However, some studies doubt this suggestion. [6]
NGC 1232 and its apparent companions are possibly part of the Eridanus cluster of galaxies, along with NGC 1300.
NGC 1232 is a face-on spiral galaxy. It can be technically considered a grand-design galaxy and is considered a prototype for multi-arm spiral galaxies. [7] Its galactic bulge is small. While NGC 1232 is classified as an intermediate spiral galaxy, the bulge shows hints of a galactic bar. [7]
NGC 1232's spiral arms are bright and flocculent, winding counterclockwise from the galactic center. They contain numerous HII regions. [7] At large distances from the galaxy's center, the spiral arms either branch out and disperse, producing long spiral arms, or connect with arm segments. [8] However, they are not smooth as expected for a spiral galaxy. Instead, they bend abruptly and show significant deviations from a constant pitch. In fact, the same pitch angle cannot be applied to one arm due to the arms deviating. Astronomer Halton Arp suggested that this is the result of a galaxy interaction. That the galaxy contains numerous star-forming regions makes it an excellent laboratory when it comes to studies on star formation. [4]
Most of NGC 1232's arms and arm segments widen as they get farther and farther away from the galaxy's center with only one arm or arm segment, designated as arm segment "E", narrowing as it gets further from the center. This is likely due to less and less star formation occurring at farther distances from the galaxy's center, or it may be because the spiral arm reaches a point where the spiral pattern starts to co-rotate orbiting material. [8]
NGC 1232 and NGC 1232 A may both be associated with the Eridanus cluster of galaxies, but with a distance of around 2.2 million parsecs from the cluster's center, they may not be bound to the cluster. [7]
It was originally thought that one of NGC 1232's companions, NGC 1232A, was interacting with NGC 1232 and causing perturbations within its disk, as NGC 1232A seems to be a satellite galaxy of NGC 1232 at first sight, [9] but this is likely not the case. In 1988, NGC 1232A was estimated to be 68 million light-years away [10] while NGC 1232 was estimated to be 65 million light-years away. [2] The redshifts of the two galaxies do not match, which suggest that they likely never interacted before and are not currently interacting. The discrepant redshifts for the two galaxies is one of the reasons why the pair is known as one of the most striking examples for discrepant redshifts in galaxy pairs. [6] Instead, X-Ray studies suggest that NGC 1232 may have interacted with a dwarf galaxy, but the dwarf galaxy has apparently left no remnant. [4]
X-Ray observations over a three-year period made by the Chandra X-ray observatory also suggest that there was an interaction between NGC 1232 and another dwarf galaxy, commenting on a massive cloud of gas only visible in the X-ray superimposed on NGC 1232's images. The paper concludes that this may be the first case of the dwarf galaxy-large galaxy collision whose evidence is only visible in the X-Ray. However, it is noted that this may be due to other causes, such as numerous supernovae, but the study also suggests that there is no other evidence for this. [5] As a result, an interaction with another galaxy, other than NGC 1232A, is sometimes thought to be the cause of unusual bending in the spiral arms. In 2018, a study of the star formation rates in NGC 1232 took images of the galaxy in Hydrogen Alpha, finding over 970 HII regions. It is remarked that there is a concentration of HII regions in one part of the galaxy, but when the star-formation rates are taken into account, the concentration is more diluted. The study found that X-Ray emissions may be quenching star formation in some areas of the galaxy, because there seems to be lower concentration of HII regions there. The amount of HII regions seems to be higher in areas without much X-ray emission. Both of these were suggested to have been caused by a collision with another galaxy. [4]
In contrast with previous studies, a recent X-Ray study remarks that the hot gas luminosity in NGC 1232 is not very high. According to the study, the cloud claimed to be superimposed on NGC 1232 does not exist, and that peculiarities in NGC 1232's HII regions are just coincidental. The study notes that NGC 1232's disk is not very warped. Thus, the study concludes that there was no interaction between either NGC 1232A or another dwarf galaxy and NGC 1232 at all. [6]
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NGC 1512 is a barred spiral galaxy approximately 38 million light-years away from Earth in the constellation Horologium. The galaxy displays a double ring structure, with a (nuclear) ring around the galactic nucleus and an (inner) further out in the main disk. The galaxy hosts an extended UV disc with at least 200 clusters with recent star formation activity. NGC 1512 is a member of the Dorado Group.
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NGC 6872, also known as the Condor Galaxy, is a large barred spiral galaxy of type SB(s)b pec in the constellation Pavo. It is 212 million light-years (65 Mpc) from Earth. NGC 6872 is interacting with the lenticular galaxy IC 4970, which is less than one twelfth as large. The galaxy has two elongated arms with a diameter based on ultraviolet light of over 522,000 light-years (160,000 pc), and a D25.5 isophotal diameter of over 717,000 light-years (220,000 pc), making it the largest known spiral galaxy. It was discovered on 27 June 1835 by English astronomer John Herschel.
The Eridanus Group, sometimes called the Eridanus Cloud, is a nearby loose grouping of galaxies at a mean distance of approximately 75 Mly in the constellation Eridanus. Redshift values show that there are approximately 200 galaxies associated with the group, approximately 70% of which are spiral and irregular type galaxies while the remaining 30% are elliptical and lenticular types.
NGC 908 is an unbarred spiral galaxy in the constellation Cetus. It was discovered in 1786 by William Herschel. This galaxy is 56 million light years away from Earth. It is the main galaxy in the NGC 908 group, which also includes NGC 899, NGC 907, and IC 223.
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NGC 2336 is a barred spiral galaxy located in the constellation Camelopardalis. It is located at a distance of circa 100 million light years from Earth, which, given its apparent dimensions, means that NGC 2336 is about 200,000 light years across. It was discovered by Wilhelm Tempel in 1876.
NGC 2835 is an intermediate spiral galaxy located in the constellation Hydra. It is located at a distance of circa 35 million light years from Earth, which, given its apparent dimensions, means that NGC 2835 is about 65,000 light years across. It was discovered by Wilhelm Tempel on April 13, 1884. NGC 2835 is located only 18.5 degrees from the galactic plane.
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NGC 4848 is a barred spiral galaxy in the constellation Coma Berenices. It is circa 340 million light-years from Earth, which, given its apparent dimensions, means that NGC 4848 is about 170,000 light years across. It was discovered by Heinrich d'Arrest on April 21, 1865. It is considered part of the Coma Cluster, which is in its northwest part. The galaxy has been stripped of its gas as it passed through the cluster.
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