Far ultraviolet ( FUV ) imagery of the edge-on , Sc/SBd galaxy , NGCÂ 4631 reveals very strong FUV emission , resulting from active star formation , uniformly distributed along the galactic mid- plane .
Multi-band imagery , H i and H ii position-velocity curves and extinction considerations all imply that the emission is from the outer edges of the visible galaxy .
The overall FUV morphology of this edge-on disk system is remarkably similar to those of the so-called “ chain galaxies ” evident at high redshift , thus suggesting a similar interpretation for at least some of those distant objects . FUV,U,B and V magnitudes , measured for 48 star forming regions , along with corresponding H \alpha and H \beta measurements are used to construct diagnostic color-color diagrams .
Although there are significant exceptions , most of the star forming regions are less massive and older than 30Â Doradus .
Comparison with the expectations from two star formation models yields ages of 2.7 to 10Â Myr for the instantaneous burst ( IB ) model and star formation cut-off ages of 0 to 9Â Myr for the continuous star formation ( CSF ) model .
Interpreted in terms of the IB model the photometry implies a total created mass in the 48 star forming regions of 2.5 \times 10 ^ { 7 } Â M _ { \sun } .
When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33Â M _ { \sun } Â yr ^ { -1 } .
These results are compared to those derived from FIR and radio observations .
Corrections for FUV emission reprocessed by interstellar grains are estimated .

A large ring , \sim 3Â kpc in diameter , of 14 star forming regions is concentrically located with an expanding H i shell ( 38 ) toward the eastern end of the galaxy .
Our observations imply that the shell may have been generated primarily by supernovae arising from 5.3 \times 10 ^ { 4 } OB stars in a massive star forming region beginning about 20Â Myr ago , and that the presently observed FUV bright emission is due to second generation stars .