Numerous Old Starburst Galaxies in the Local Universe
  Old starburst galaxies are deficient in O stars, and hence do not exhibit strong line emission in the optical regime. However, there remain many B stars, which are expected to heat dust grains and generate strong continuum emission in the far-infrared. The IRAS data for a statistically complete sample of nearby galaxies reveal for the first time that such objects are as numerous as 30-40% of the local galaxy population. 
H. Mouri and Y. Taniguchi