NGC 7331 Group
Visual grouping of galaxies in the constellation Pegasus
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":
- NGC 7335: A lenticular galaxy located 290 million light-years (89 Mpc) away
- NGC 7336: A spiral galaxy located 370 million light-years (113 Mpc) away
- NGC 7337: A barred spiral galaxy located 300 million light-years (92 Mpc) away
- NGC 7340: An elliptical galaxy located 290 million light-years (89 Mpc) away
01Physical 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.
The true physical group bound to NGC 7331 consists of several satellite dwarf galaxies at matching distances, and NGC 7320 (which visually overlaps Stephan's Quintet), UGC 1206), and UGC 12160.
02Nomenclature 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.
Sources and credits
This article is adapted from the Wikipedia article “NGC 7331 Group”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- PIA21088 - Supernova SN 2014C (Optical and X-Ray), Unannotated Version.jpg by X-ray images: NASA/CXC/CIERA/R.Margutti et al; Optical image: SDSS, Public domain
- Deer Lick region.jpg by Alpha Zhang (AstroBin: shyzhang127), CC BY-SA 4.0
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