NGC 7331 Group

NGC 7331 Group
NGC 7331, along with NGC 7335, 7336, 7337 and 7340
Observation data (Epoch J2000)
ConstellationPegasus
Right ascension22h 37m
Declination+34° 25′
Brightest memberNGC 7331
Number of galaxies5
Parent structurePerseus–Pisces Supercluster
Other designations
NGC 7331 Group, LGG 459, Deer Lick Group, Holm 795

The NGC 7331 Group is a visual grouping of galaxies located in the constellation Pegasus. The system is anchored by its largest member, NGC 7331, which lies approximately 40 million light-years (12.3 Mpc) from Earth.

Apparent directly northeast of NGC 7331 are four smaller and much fainter galaxies, known as "the fleas":

Physical vs. visual association

Although historical catalogs grouped these objects together due to their visual close proximity, spectroscopic measurements from the NASA/IPAC Extragalactic Database (NED) confirm that the group is an optical grouping caused by line-of-sight alignment rather than a gravitationally bound cluster.

While NGC 7331 sits in the foreground at a heliocentric radial velocity of 816 km/s (redshift 0.002722), the four background companion galaxies exhibit recessional velocities between 6,200 km/s and 8,800 km/s (redshift 0.021 to 0.029 Z). As a result, the four companion galaxies sit at distances ranging from 290 to 370 million light-years.

Image of NGC 7331 Group with Stephan's Quintet on the lower right side

The true physical group bound to NGC 7331 consists of several satellite dwarf galaxies at matching distances, NGC 7363 and NGC 7320 (which visually overlaps Stephan's Quintet), UGC 1206), and UGC 12160.

Nomenclature and history

NGC 7331 was discovered by astronomer William Herschel on September 6, 1784. Swedish astronomer Erik Holmberg cataloged the visual system as Holm 795 in his 1937 study of multiple galaxies.

The popular informal name "Deer Lick Group" was coined in the 1980s by American amateur astronomer Tom Lorenzin to commemorate an exceptional viewing session at the Deerlick Gap Overlook along the Blue Ridge Parkway in North Carolina, where he observed NGC 7331 along with its faint background companion galaxies.

See also

References

  1. 1 2 3 4 5 6 Kruesi, Liz (21 March 2022). "101 Must-See Cosmic Objects: NGC 7331". Astronomy Magazine. Retrieved 22 July 2026.
  2. 1 2 "NASA/IPAC Extragalactic Database Results for NGC 7331". NASA/IPAC Extragalactic Database. Retrieved 22 July 2026.
  3. ↑ Garcia, A. M. (July 1993). "General study of group membership. II. Determination of nearby groups". Astronomy and Astrophysics Supplement Series. 100: 47–90. Bibcode:1993A&AS..100...47G.
  4. ↑ Holmberg, Erik (1937). "A Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems". Annals of the Observatory of Lund. 6: 1–173. Bibcode:1937AnLun...6....1H.