The relative abundances of ellipticals and starbursts among the extremely red galaxies

We present J-band observations of a complete sample of 57 red galaxies selected to have K' < 20 and R - K' > 5.3. We use a prescription based on the R - K and J - K colours, to separate the two dominant populations, old ellipticals and dusty starbursts. We find that both populations are present in the current sample and have similar abundances, and discuss the uncertainties in this result. Galactic stars comprise about 9 per cent of the objects. The starburst galaxies of the present sample are found to give a contribution to the cosmic star formation density similar to the Lyman-break galaxies.