Ring Galaxies

Ring galaxies  are believed to  form when   a compact smaller galaxy plunges  through  the center of a larger more 
diffuse rotating disk galaxy.  The galaxy in transit exerts a brief  inward pull on the stars of the target galaxy, 
which execute radial harmonic oscillations in addition to their initial  circular motion. A series  of ring  waves 
forms and propagates through the target disk, as numerical simulations have convincingly demonstrated (e.g., Lynds  
& Toomre 1976; Theys & Spiegel 1977). These  radially expanding  waves are accompanied by a  strong burst  of star 
formation: observed ring galaxies are usually very blue and possess large HII regions (Theys & Spiegel 1976; Jeske 
1986). This is the classical ring galaxy II Hz 4 that was modeled by Lynds & Toomre (1976).

NGC 442	NGC 660	M 77	UGC 4261	UGC 4332	NGC 2628
NGC 2685	UGC 4892	UGC 5101	UGC 5119	M 82	NGC 5964
UGC 5485	NGC 3310	*NGC 3384	NGC 3406 NED01	UGC 6182	NGC 5921
NGC 3718	NGC 3998	NGC 4203	NGC 4262	UGC 7388	NGC 4370
UGC07636	*NGC 4643	NGC 4753	NGC 5103	IC 883	M 51a
NGC 5544	ARP199	UGC 9562	UGC 9796	PRCD-51	NGC 6028
UGC 10205	NGC 1042	M 77	NGC 2775	*NGC 3184	M 095
M 096	NGC 3631	NGC 3726	NGC 3810	NGC 4030	NGC 4051
NGC 4123	NGC 4242	NGC 4535	M 058	NGC 4618	M 94
NGC 5248	NGC 5334	*NGC5371	M 101	NGC 5474	NGC 5850
NGC2685	NGC2859	NGC3945	NGC4612	UGC 10205