Copeland Septet
Group of galaxies in the constellation Leo
Copeland's Septet is a compact group of interacting galaxies located approximately 430 million light-years (132 Mpc) away in the constellation Leo. Although historically named a septet due to the seven primary galaxies detected in 19th-century visual observations, modern astronomical catalogs identify eight individual physical members within the group, designated HCG 57a through HCG 57h. The redshift of the brightest member, NGC 3753 places Copelands Septet as a part of the Coma Supercluster.
01Member Components
The group is dominated by NGC 3753 (HCG 57a), a magnitude 14.5 spiral galaxy and the largest component in the group. NGC 3753 forms a close physical pair with NGC 3754 (HCG 57d), a smaller spiral galaxy located immediately adjacent to it. Directly next to this pair is NGC 3750 (HCG 57c), an elliptical galaxy occupying the central region of the group core.
The western portion of the cluster contains NGC 3746 (HCG 57b), a barred spiral galaxy that has hosted two documented supernovae (SN 2002ar and SN 2005ba), and NGC 3748 (HCG 57e), an edge-on lenticular galaxy with a dust lane. The remaining cataloged components are NGC 3751 (HCG 57f), an elliptical galaxy on the southern edge of the core, NGC 3745 (HCG 57g), a faint lenticular galaxy, and PGC 36010 (HCG 57h), a 17th-magnitude dwarf spiral galaxy.
Gravitational Interactions
The members of Copeland's Septet show evidence of strong tidal disruption caused by mutual gravitational encounters. Tidal interaction between NGC 3753 and NGC 3754 has drawn out long filaments of neutral hydrogen gas and stars into the intergalactic medium. Spectroscopic studies show that tidal forces have distorted galaxy disks and driven gas stripping throughout the cluster, triggering star formation within the spiral members.
02Discovery and History
British astronomer Ralph Copeland discovered the cluster on February 9, 1874, while observing from Birr Castle in Ireland using the 72-inch reflecting telescope. Copeland recorded seven visual members in the field and published the group under the title "The Septet."
In 1982, Paul Hickson included the system as entry 57 in his catalogue of compact galaxy groups, adding the faint dwarf galaxy PGC 36010 to the group designation as HCG 57h.
Sources and credits
This article is adapted from the Wikipedia article “Copeland Septet”, 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:
- Copeland Septet group of galaxies.jpg by DESI Legacy Imaging Surveys/LBNL/DOE & KPNO/CTIO/NOIRLab/NSF/AURA, CC BY 4.0
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