  HCG 54 has been classified as a compact galaxy group by Hickson, but its
nature is uncertain because of its unusual properties. We present here a study
of HCG~54 based on deep optical images and spectroscopy as well as high spatial
and spectral resolution HI observations obtained at the VLA. Both optical and
radio data indicate clearly that HCG~54 is a product of a recent merger
involving at least two galaxies. Our optical images have revealed a blue
elongated structure associated with HCG 54a embedded in a rounder and redder
stellar envelope. Several ripples or shells whose center is located near HCG
54a and b are also detected. These observed features are similar to those found
in the numerical simulations of tidal interactions involving two equal mass
disk galaxies. This system is embedded in an HI cloud 12 kpc in diameter, and a
20 kpc HI tidal tail emerges from its western edge. Both the HI distribution
and kinematics are consistent with a recent history of a deeply penetrating
interaction or a merger. Based on the analysis of our new data we propose that
HCG 54 is the remnant of a merger in an advanced stage, whose main body is what
has been called HCG 54a, while HCG 54b marks the location of a strong starburst
induced by the interaction, as evidenced by the Wolf Rayet stellar population
that we detect. Optical spectra of HCG 54c and d show HII region features and
are interpreted as tidal debris of the collision undergoing active star
formation.
