Sign on
ADS Classic is now deprecated. It will be completely retired in October 2019. Please redirect your searches to the new ADS modern form or the classic form. More info can be found on our blog.

SAO/NASA ADS Astronomy Abstract Service

· Find Similar Abstracts (with default settings below)
· Full Refereed Journal Article (PDF/Postscript)
· Full Refereed Scanned Article (GIF)
· References in the article
· Citations to the Article (91) (Citation History)
· Refereed Citations to the Article
· SIMBAD Objects (1)
· NED Objects (1)
· Also-Read Articles (Reads History)
· Translate This Page
Counterrotating stars in the disk of the SAB galaxy NGC 7217
Merrifield, Michael R.; Kuijken, Konrad 
AA(Department of Physics, University of Southampton, Highfield SO 9 5NH, UK), AB(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 2, p. 575-589 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Counter Rotation, Disk Galaxies, Dynamic Models, Galactic Bulge, Kinematics, Spiral Galaxies, Velocity Distribution, Angular Momentum, Astronomical Models, Galactic Evolution, Quadratic Programming, Rotating Disks
Bibliographic Code:


We have analyzed high signal-to-noise spectra of the disk galaxy NGC 7217 in order to extract the full line-of-sight velocity distribution along both its major and minor axes. The data reveal that 20%-30% of the stars in this galaxy are in a distinct component on retrograde orbits. This counterrotating population cannot be explained away as a systematic error, and it does not seem to be caused by the bulge's contribution to the velocity distribution. We have developed a new technique for fitting dynamical disk models directly to the galaxy spectra, and application of this method confirms the presence of the distinct counterrotating disk population. NGC 7217 is only the second disk galaxy known to contain counterrotating stars, but we argue that similar components in other regular disk systems would not have been detected by traditional techniques, and so there could exist many such systems. The existence of disk stars on retrograde orbits provides a new clue as to the manner in which the galaxy formed: it favors a scenario in which matter continues to accrete onto the galaxy over a long period of time, with rapid, substantial changes occurring in the angular momentum of the infalling material. The observable consequences of this evolutionary history include a large bulge-to-disk ratio and the absence of strong spiral structure, and so the presence or absence of a counterrotating component may go some way toward explaining the Hubble sequence for disk galaxies.

Printing Options

Print whole paper
Print Page(s) through

Return 600 dpi PDF to Acrobat/Browser. Different resolutions (200 or 600 dpi), formats (Postscript, PDF, etc), page sizes (US Letter, European A4, etc), and compression (gzip,compress,none) can be set through the Printing Preferences

More Article Retrieval Options

HELP for Article Retrieval

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Find Similar Abstracts:

Use: Authors
Keywords (in text query field)
Abstract Text
Return: Query Results Return    items starting with number
Query Form
Database: Astronomy
arXiv e-prints