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A Counter-rotating Bulge in the Sb Galaxy NGC 7331
Astrophysics · Submitted 27 Feb 1996
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk.
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The paper's own sentences, arranged. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
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The abstract, sentence by sentence
We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1 -- 1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky. Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). Another possibility however is that the structure has been there since the formation of the galaxy. In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. | result 0.98 | 0.97 | 0.89 | asserted 1.00 |
| s1 | Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1 -- 1.5. | result 0.74 | 0.95 | 0.12 | asserted 1.00 |
| s2 | The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. | result 1.00 | 0.91 | 0.08 | asserted 1.00 |
| s3 | At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky. | result 0.99 | 0.84 | 0.04 | asserted 1.00 |
| s4 | Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. | contribution 0.39 | 0.73 | 0.43 | asserted 0.83 |
| s5 | If it is a bar seen end-on, this bar has to be thicker than the disk. | interpretation 0.97 | 0.34 | 0.04 | hedged possibility 0.72 |
| s6 | We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. | result 0.96 | 0.95 | 0.56 | asserted 1.00 |
| s7 | The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). | interpretation 1.00 | 0.43 | 0.12 | hedged possibility 0.91 |
| s8 | Another possibility however is that the structure has been there since the formation of the galaxy. | interpretation 1.00 | 0.14 | 0.03 | hedged possibility 0.93 |
| s9 | In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially. | interpretation 0.97 | 0.19 | 0.04 | asserted 0.43 |
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The paper
Original abstract
We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1 -- 1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky. Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). Another possibility however is that the structure has been there since the formation of the galaxy. In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.
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