Star formation rates (SFR) in ring galaxies are typically
5
M
yr-1,
i.e., somewhat enhanced over large spirals but far below the SFRs
inferred in LIRGs (cf.
Appleton & Struck 1987;
Higdon 1995;
Higdon & Wallin 1997;
Sanders & Mirabel 1996).
However, the distribution of star formation is unique, being
completely restricted to the expanding rings while simultaneously
extinguished over the interior disk. Both effects are evident in the
Lindsay-Shapley ring (L-S, hereafter) and Cartwheel,
shown in Figure 1. A weak nuclear source is
responsible for 5% of the star formation in both.
![]() |
Figure 1. A polychromatic view of two ring
galaxies: (top) the L-S ring galaxy (SFR = 8
M |
The star forming rings are narrow, with slices showing very sharp radial
cutoffs in
H emission. This implies
that OB stars remain in the rings for their Main Sequence lifetimes,
which constrains the stellar velocity dispersion of the rings:
*
<
rring
/
OB
45 km s-1.
The weak line emission that is sometimes found in ring galaxy disks
is post-starburst in origin, i.e., arising from aging HII
complexes powered by A-stars.