De Vaucouleurs system
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The de Vaucouleurs system, also known as the revised Hubble system, is a comprehensive galaxy morphological classification scheme developed by French astronomer Gérard de Vaucouleurs in 1959.[1] It extends Edwin Hubble's original tuning-fork classification into a three-dimensional parameter space that describes the structural complexity of galaxies.[2]
Historical Development
Origins (1950s)
Gérard de Vaucouleurs (1918–1995) began developing his classification system while working at Mount Stromlo Observatory in Australia (1951–1957), continuing at Lowell Observatory (1957–1958) and Harvard College Observatory (1958–1960).[3] His seminal 1959 paper "Classification and Morphology of External Galaxies," published in Handbuch der Physik, introduced a fundamental revision to Hubble's 1926 scheme.[1]
De Vaucouleurs recognized that Hubble's two-dimensional "tuning fork" diagram could not adequately represent the full diversity of galaxy morphologies.[2] In particular, Hubble's system did not explicitly account for:
- Barred structures in lenticular galaxies
- Ring structures in both barred and unbarred galaxies
- Transition types between ellipticals and spirals
- Late-type spirals beyond Hubble's Sc category[2]
Reference Catalogues (1960s–1990s)
In 1960, de Vaucouleurs joined the University of Texas at Austin as one of the first five faculty members in the newly formed astronomy department, where he spent the remainder of his career.[3] Working with his wife and collaborator Antoinette de Vaucouleurs (1921–1987), he applied his classification system to thousands of galaxies observed at McDonald Observatory.[3]
The Reference Catalogue of Bright Galaxies (RC1) was published in 1964, classifying 2,599 galaxies.[4] This was followed by the Second Reference Catalogue (RC2) in 1976 and the Third Reference Catalogue (RC3) in 1991, each expanding the sample and refining the classification criteria.[5]
The Modern Atlas (2007)
In 2007, astronomers Ronald J. Buta, Harold G. Corwin, and Stephen C. Odewahn published The de Vaucouleurs Atlas of Galaxies through Cambridge University Press.[2] This comprehensive work illustrated 400 nearby galaxies using modern CCD imagery, updating de Vaucouleurs's original photographic plates for the digital era.[2]
The Three-Dimensional Classification Volume
The fundamental innovation of the de Vaucouleurs system is its representation of galaxy morphology as a three-dimensional classification volume, in contrast to Hubble's two-dimensional tuning fork.[2]
| Axis | Parameter | Symbol | Range |
|---|---|---|---|
| X (horizontal) | Stage | T | −5 to +10 |
| Y (vertical) | Family | A, AB, B | SA, SAB, SB |
| Z (depth) | Variety | r, rs, s | (r), (rs), (s) |
Stage Parameter (T)
The stage parameter provides a numerical index along the morphological sequence, enabling quantitative analysis and computer database applications.[1]
Stage Index Values
| T | Type | Description |
|---|---|---|
| −5 to −3 | E | Ellipticals |
| −2 | S0⁻ | Early lenticulars |
| −1 | S0 | Lenticulars |
| 0 | S0/a | S0–spiral transition |
| 1 | Sa | Early spirals |
| 2 | Sab | Intermediate |
| 3 | Sb | Moderate spirals |
| 4 | Sbc | Intermediate |
| 5 | Sc | Late spirals |
| 6 | Scd | Very late |
| 7 | Sd | Extremely late |
| 8 | Sdm | Magellanic spirals |
| 9 | Sm | Magellanic irregulars |
| 10 | Im | Irregulars |
Physical Correlations
The T index correlates strongly with physical galaxy properties:[6]
- Color: Earlier types (T < 2) are redder (B−V ~ 0.9 for ellipticals); later types (T > 5) are bluer (B−V ~ 0.5 for Sc galaxies)
- Gas content: Neutral hydrogen (HI) mass fraction increases from <1% in ellipticals to >50% in irregulars
- Star formation: Specific star formation rate correlates positively with T
- Mass concentration: Bulge-to-total luminosity ratio decreases from ~0.9 in ellipticals to ~0.1 in late spirals
Family Parameter (Barredness)
The family parameter describes the presence and strength of a central bar structure.[1]
| Symbol | Name | Bar Strength | Example |
|---|---|---|---|
| SA | Nonbarred | None | Messier 81 |
| SAB | Weakly barred | Intermediate | Messier 83 |
| SB | Strongly barred | Prominent | NGC 1300 |
Approximately 60–70% of spiral galaxies show some bar structure.[2]
Variety Parameter (Ring Structure)
The variety parameter characterizes the presence of inner ring structures, which form at resonance locations in the galactic disk.[2]
| Symbol | Name | Structure |
|---|---|---|
| (r) | Ringed | Complete inner ring |
| (rs) | Pseudoring | Partial/broken ring |
| (s) | Spiral | No ring |
Extended Notation
Outer Rings
Outer ring structures are prepended to the classification:[1]
- R: Definite outer ring (e.g., RSB(r)bc)
- (R): Outer pseudoring (e.g., (R)SA(rs)ab)
Arm Classes
De Vaucouleurs distinguished arm morphology:[1]
- m: Massive arms—broad, diffuse
- f: Filamentary arms—thin, knotty
Scientific Applications
Galaxy Evolution
The de Vaucouleurs system provides a framework for studying galaxy evolution:[2]
- Ram-pressure stripping: Late-type spirals (Sc–Sd) transform to S0 in dense clusters
- Morphology–density relation: Early types dominate cluster cores; late types populate the field
Modern Surveys
The system remains standard in:[7]
- Sloan Digital Sky Survey (SDSS)
- Galaxy Zoo citizen science project
- 2MASS infrared morphology studies
Limitations
Despite its widespread use, the system has limitations:[2]
- Subjectivity: Visual classification depends on observer experience
- Wavelength dependence: Morphology varies with observation wavelength
- High-redshift effects: Surface brightness dimming complicates distant galaxy classification
See Also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 de Vaucouleurs, Gérard (1959). "Classification and Morphology of External Galaxies". Handbuch der Physik. 53: 275–310. Bibcode:1959HDP....53..275D. doi:10.1007/978-3-642-45932-0_7.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Buta, Ronald J.; Corwin, Harold G.; Odewahn, Stephen C. (2007). The de Vaucouleurs Atlas of Galaxies. Cambridge University Press. ISBN 978-0-521-82048-6. Search this book on
- ↑ 3.0 3.1 3.2 "Gerard Henri de Vaucouleurs (1918–1995)". Bulletin of the American Astronomical Society. 28 (4): 1449–1451. 1996. Bibcode:1996BAAS...28.1449B.
- ↑ de Vaucouleurs, Gérard; de Vaucouleurs, Antoinette (1964). Reference Catalogue of Bright Galaxies. University of Texas Press. Search this book on
- ↑ de Vaucouleurs, Gérard; de Vaucouleurs, Antoinette; Corwin, Harold G.; Buta, Ronald J.; Paturel, Georges; Fouqué, Pascal (1991). Third Reference Catalogue of Bright Galaxies. Springer-Verlag. ISBN 978-0-387-97549-8. Search this book on
- ↑ Strateva, I.; et al. (2001). "Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data". The Astronomical Journal. 122 (4): 1861–1874. arXiv:astro-ph/0107201. Bibcode:2001AJ....122.1861S. doi:10.1086/323297.
- ↑ Lintott, C. J.; et al. (2008). "Galaxy Zoo: Morphologies Derived from Visual Inspection of Galaxies from the Sloan Digital Sky Survey". Monthly Notices of the Royal Astronomical Society. 389 (3): 1179–1189. arXiv:0804.4483. Bibcode:2008MNRAS.389.1179L. doi:10.1111/j.1365-2966.2008.13689.x.
External Links
- Galaxy Morphology and Classification — NASA/IPAC
- The de Vaucouleurs Atlas — Cambridge University Press
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