Using the HST WFPC2 we perform deep I -band imaging of 9 radio-selected ( F ( 8.5 ~ { } GHz ) \geq 14 \mu Jy ) faint galaxies from the Roche , Lowenthal and Koo ( 2002 ) sample .
Two are also observed in V using HST STIS .

Six of the galaxies have known redshifts , in the range 0.4 < z < 1.0 .
Radial intensity profiles indicate that 7 are disk galaxies and 2 are bulge-dominated .
Four of the six with redshifts have a high optical surface brightness in comparison with previous studies of disk galaxies at similar redshifts ( e.g .
Lilly et al .
1998 ) .
The HST imaging reveals that 2 of the 9 galaxies are in close interacting pairs and another 5 show morphological evidence of recent interactions – two are very asymmetric ( A _ { asym } \sim 0.4 ) and , three have large , luminous rings resembling the collisional starburst rings in the Cartwheel galaxy .
For the two ring galaxies with redshifts , we measure ring radii of 7.05 and 10.0 h ^ { -1 } _ { 50 } kpc , which suggest post-collision ages 0.1–0.2 Gyr .
One has a fainter inner ring , like the original Cartwheel .
The remaining two appear to be late-type barred galaxies and relatively undisturbed .

Our HST imaging confirms the high incidence of interactions and dynamical disturbance in faint radio-selected galaxies , as reported by e.g .
Windhorst et al .
( 1995 ) and Serjeant .
et al .
( 2000 ) .
In the great majority of these galaxies the high radio luminosities are probably the result of interaction-triggered starbursts .
However , one interacting galaxy is a very radioluminous giant elliptical , with red V - I colours , a normal surface brightness and no evidence of star-forming regions , so its radio source is probably an obscured AGN .
The mixture of observed morphologies suggests that enhanced radio luminosities often persist to a late stage of interaction , i.e .
at least \sim 0.2 Gyr after the perigalactic encounter .