NGC 3175
A weakly-barred spiral galaxy viewed nearly edge-on.
NGC 3175 is a spiral galaxy in the far eastern part of the southern constellation Antlia, roughly 54 million light-years away. It gives its name to the NGC 3175 group, which also includes the spiral galaxy NGC 3137.
English astronomer John Herschel discovered it on March 30, 1835, describing it as "considerably bright, large, much extended NE-SW, very gradually little brighter middle." Classified as SAB(s)b, it is a weakly barred spiral galaxy with no inner ring and moderately tight spiral arms. Its major axis runs at a position angle of 56°, and the galaxy is tilted 77° relative to Earth’s line of sight, making it appear nearly edge-on.
Observations with the Australia Telescope Compact Array revealed that the outer disk—beyond a certain radius from the core—lacks neutral hydrogen, meaning no star formation occurs there, an unusual trait for a spiral. In contrast, the central region contains neutral hydrogen and is actively forming stars. No nearby galaxies are present that could have stripped the hydrogen from the outer parts.
Quick Facts
- Epoch
- J2000
- Constellation Name
- Antlia
- Ra
- 10 · 14 · 42.111
- Dec
- -28 · 52 · 19.42
- Z
- 0.003613
- Dist Ly
- 16.52 Mpc
- Group Cluster
- NGC 3175 group
- Mass Light Ratio
- 7.13 · 1.78 · 1.98
- Appmag B
- 12.08
Facts from the source article.
Lore & Background
NGC 3175 was discovered on March 30, 1835 by English astronomer John Herschel, whose notes described it as 'considerably bright, large, much extended NE-SW, very gradually little brighter middle'. Its morphological classification is SAB(s)b, indicating a weakly-barred spiral galaxy with no inner ring structure and somewhat tightly wound spiral arms. The galaxy spans an angular size with the major axis aligned along a position angle of 56°, and its plane is inclined at an angle of 77° to the line of sight from Earth, thus being viewed close to edge-on.
A study using the Australia Telescope Compact Array found that the outer disk of this galaxy, beyond a radius from the core, is free of neutral hydrogen emission, indicating that no star formation is occurring there—a peculiar feature for a spiral galaxy. In contrast, the central region is undergoing star formation and contains neutral hydrogen. There are no nearby galaxies that could explain the stripping of hydrogen gas from the outer part of the galaxy.
Reader's Guide
NGC 3175 is notable as the namesake of the NGC 3175 group of galaxies, which includes the spiral galaxy NGC 3137. Its peculiar outer disk, which lacks neutral hydrogen and star formation, presents an interesting case for understanding galaxy evolution, as no nearby galaxies are present to account for the gas stripping. The galaxy's close-to-edge-on orientation (inclination 77°) and its classification as a weakly-barred spiral (SAB(s)b) provide valuable data for studies of spiral structure and bar dynamics. Discovered by John Herschel in 1835, it remains a subject of astronomical interest, particularly for its unusual hydrogen distribution and the contrast between its active central star formation and inert outer regions.
Did You Know?
- NGC 3175 was discovered by English astronomer John Herschel on March 30, 1835.
- The galaxy's outer disk is free of neutral hydrogen emission, indicating no star formation there.
- The galaxy is viewed nearly edge-on, with an inclination of 77° to the line of sight.
More in NGC Objects, Part 5 1-24
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