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EVAC Hickson Compact (Galaxy) Group
(HCG) Program
Compact Galaxy Groups have been of interest to astronomers ever since the discovery of Stephan’s
Quintet (Hickson 92) in 1877. The Hickson Compact Galaxy Groups were compiled by Paul Hickson and
published in his Atlas of Compact Groups of Galaxies in 1994. They represent the brightest grooups
visible to northern observers and this makes them ideal targets for amateur astronomers. The Hickson
100 list represents those groups with a minimum of four (4) galaxy members.
According to Hickson: “Most compact groups contain a high fraction of galaxies having morphological or
kinematical peculiarities, nuclear radio and infrared emission, and starburst or active galactic nuclei
(AGN) activity. They contain large quantities of diffuse gas and are dynamically dominated by dark
matter. They most likely form as subsystems within looser associations and evolve by gravitational
processes. Strong galaxy interactions result and merging is expected to lead to the ultimate demise of
the group. Compact groups are surprisingly numerous, and may play a significant role in galaxy
evolution.”[3]
containing links to the observed images
The Hickson observations are actually used in two Observing Programs. The EVAC program covers the
observation of all 100 objects.
A separate program, from the Astronomical League (AL), is the Galaxy Groups and Clusters program.
The AL program requires 30 of the 100 Hickson groups be observed (any 30 of the 100). In addition, it
requires 30 of a list of 50 galaxy “trios” from the Atlas of Compact Galaxy Trios; 30 from a list of 50
“Additional galaxy Groups”, and another 30 of 50 selected Abell Clusters.
