Astronomy:NGC 7320

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NGC 7320
NGC 7320 imaged by the Hubble Space Telescope
Observation data (J2000.0 epoch)
ConstellationPegasus
Right ascension 22h 36m 03.4s[1]
Declination+33° 56′ 53″[1]
Redshift786 ± 20 km/s[1]
Distance39 million ly (12 Mpc)[2]
Apparent magnitude (V)+13.2[1]
Apparent magnitude (B)13.8[3]
Absolute magnitude (V)−17.8[3]
Absolute magnitude (B)−16.6[3]
Characteristics
TypeSA(s)d[1]
Size9.56 kiloparsecs (31,170 light-years) (diameter; 25.0 mag/arcsec2 B-band isophote)[1]
Apparent size (V)2.2′ × 1.2′[1]
Notable featuresForeground projection on Stephan's Quintet
Other designations
UGC 12101, PGC 69270, Arp 319, HCG 092A[1]

NGC 7320 is an unbarred spiral galaxy located approximately 39 million light-years away in the constellation Pegasus. It was discovered on 27 September 1873 by the French astronomer Édouard Stephan.[4]

While visually grouped as the brightest apparent member of Stephan's Quintet (Hickson Compact Group 92), NGC 7320 is not gravitationally associated with the core interacting cluster. It is instead a foreground projection positioned along the same line of sight from Earth, lying at roughly one-seventh the distance of the background group.[5]

Observational history

Historically, the spatial location of NGC 7320 was a central point of contention in the mid-20th century cosmic distance scale debate. Spectroscopic observations obtained by Geoffrey and Margaret Burbidge in 1961 revealed a discordant heliocentric redshift of 786 km/s for NGC 7320, contrasted against the ~6,600 km/s velocities of the surrounding members.[6] Anomalous redshift proponents argued this indicated physical proximity with non-cosmological redshift factors. However, high-resolution imaging from the Hubble Space Telescope successfully resolved individual population I stars and localized interstellar dust within NGC 7320—confirming its proximity as a foreground silhouette.[5]

Group membership

Based on its distance and spatial velocity, NGC 7320 is classified as a physical member of the nearby NGC 7331 Group (Deer Lick Group), centered around the isolated unbarred spiral galaxy NGC 7331.[7]

Physical characteristics

NGC 7320 is classified morphologically as an SA(s)d intermediate-to-late type spiral galaxy under the De Vaucouleurs profile. Unlike the structurally stripped background members of Hickson 92, NGC 7320 maintains an unperturbed interstellar medium. High-resolution infrared imaging from the James Webb Space Telescope's Mid-Infrared Instrument (MIRI) demonstrates extensive, active H II regions embedded along its outer spiral filaments, tracing massive ongoing stellar assembly cycles driven by its native cold gas reservoirs.[8]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "NASA/IPAC Extragalactic Database". Results for NGC 7320. http://nedwww.ipac.caltech.edu/. 
  2. ↑ Moles, M.; Marquez, I.; Sulentic, J. W. (1998). "The observational status of Stephan's Quintet". Astronomy and Astrophysics 334: 473–481. Bibcode: 1998A&A...334..473M. 
  3. ↑ 3.0 3.1 3.2 "NASA/IPAC Extragalactic Database Results for NGC 7320". NASA/IPAC Extragalactic Database. https://ned.ipac.caltech.edu/. 
  4. ↑ Seligman, Courtney. "New General Catalogue Objects: NGC 7320". Celestial Atlas. https://cseligman.com/text/atlas/ngc73a.htm#7320. 
  5. ↑ 5.0 5.1 "Stephan's Quintet – A Mammoth Cosmic Collision". ESA/Hubble. https://esahubble.org/news/heic0007/. 
  6. ↑ Burbidge, E. M.; Burbidge, G. R. (July 1961). "The Motions and Masses of the Galaxies in Stephan's Quintet". The Astrophysical Journal 134: 244. doi:10.1086/147134. Bibcode: 1961ApJ...134..244B. 
  7. ↑ Moles, M.; Márquez, I.; Sulentic, J. W. (June 1998). "The observational status of Stephan's Quintet". Astronomy and Astrophysics 334: 473–481. Bibcode: 1998A&A...334..473M. 
  8. ↑ "Stephan's Quintet (MIRI Imaging)". ESA/Webb, NASA, CSA. https://esawebb.org/images/weic2208b/. 

Coordinates: Sky map 22h 36m 03.4s, +33° 56′ 53″ Template:NGC objects: 7001-7840



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