The possible formation and evolution of dwarf irregular galaxies from
material derived from perturbed evolved galaxies is addressed via an H
I study of a likely example, the peculiar system NGC 5291. This syste
m, located in the western outskirts of the cluster Abell 3574, contain
s the lenticular galaxy NGC 5291 which is in close proximity to a dist
urbed companion and is flanked by an extensive complex of numerous kno
ts extending roughly 4' north and 4' south of the galaxy, In an initia
l optical and radio study, Longmore et al. (1979, MNRAS, 188, 285) sho
wed that these knots have the spectra of vigorous star-forming regions
, and suggested that some may in fact be young dwarf irregular galaxie
s. High resolution 21-cm line observations taken with the VLA are pres
ented here and reveal that the H I distribution associated with this s
ystem encompasses not only the entire N-S complex of optical knots, bu
t also forms an incomplete ring or tail that extends approximately 3'
to the west. The HI associated with NGC 5291 itself shows a high veloc
ity range; the Seashell is not detected. The formation mechanism for t
his unusual system is unclear and two models-a large, low-luminosity r
am-swept disk, and a ram-swept interaction-are discussed. The H I in t
he system contains numerous concentrations, mostly along the N-S are o
f the star-forming complexes, which generally coincide with one or mor
e optical knots; the larger H I features contain several X10(9) M-. of
gas. Each of the knots is compared to a set of criteria designed to d
etermine if these objects are bound against their own internal kinetic
energy and are tidally stable relative to the host galaxy. An analysi
s of the properties of the H I concentrations surrounding the optical
star-forming complexes indicates that at least the largest of these is
a bound system; it also possesses a stellar component. It is suggeste
d that this object is a genuinely young dwarf irregular galaxy that ha
s evolved from the material associated with the system and that this e
ntire complex contains several proto or young dwarf irregular galaxies
in various stages of development. We are therefore witnessing the ear
ly evolution of a number of genuinely young galaxies. Given the eviden
t importance of the NGC 5291 system as a ''nursery'' for young galaxie
s, careful modeling is required if we are to understand this remarkabl
e galaxy. (C) 1997 American Astronomical Society.