4. K-CORRECTIONS

Detailed spectral energy distributions, such as those reported here, will always be confined to a small sample of galaxies. The much larger amount of statistical data required for a thorough study of distant galaxies and clusters of galaxies must depend on broad-band photometry. Recently Whitford (1971) and Schild and Oke (1971) have computed K-corrections and B - V and V - R_S colors as a function of the redshift out to z = 0.28, assuming the observed energy distribution for nearby giant elliptical galaxies. Schild and Oke have extended the V - R_S calculation to z = 0.60. The present results for 3C 295 have been matched to the nearby galaxy data and used to extend the energy distribution much farther to the violet. The emission in 3727 is omitted in the combined energy distribution. This new energy distribution has been used to compute K-corrections and B - V and V - R_S colors to large values of z. The results for z 0.20 are given in Table 1; for z < 0.20 the previous results of Schild and Oke (1971) apply.

It is of note that the value of B - V reaches a maximum value at z = 0.24 and then decreases again. Similarly, a maximum value of V - R_S occurs at z = 0.50. Inspection of the normalized (B - V)_c and (V - R_S)_c colors indicates that as long as no evolutionary effects on colors occur - and this appears to be the case out to z = 0.46 - the B - V and V - R_S colors can be used to predict z. The most sensitive indicator is B - V for z < 0.16. If z lies between 0.16 and 0.48, V - R_S will give the redshift. The technique will be most valuable for clusters of galaxies where colors of several galaxies can be measured.