The galaxy population of Cl 1601+42 at z=0.54

Photometric redshifts are used to determine the rest-frame luminosity function (LF) of both early- and late-type galaxies to M-B similar to -17.6 for the cluster Cl 1601+42 at z = 0.54. The total LF shows a steep faint-end slope alpha similar to -1.4. indicating the existence of a population of numerous dwarf galaxies. Luminous galaxies, with M-B less than or similar to -19.5 are mostly red. early-type galaxies, with a LF best described by a Gaussian. Faint galaxies are predominantly blue, late-type galaxies. well fitted by a Schechter function with alpha similar to -1.7. Compared with clusters at lower redshift, the steepening of the faint end starts at brighter magnitudes for Cl 1601+42, which may indicate a brightening of the present-day dwarf population relative to the giant population with increasing redshift. Early-type galaxies are centrally concentrated, and dominate the core region. implying that the radial gradient of early-type galaxies seen in local clusters is already established at z similar to 0.5. Bright. late-type galaxies are rare, consistent with a decrease in star formation in field galaxies as they are accreted on to the cluster. while faint. blue galaxies are evenly distributed across the cluster, except for a depletion in the core region. The blue fraction is f(B) - 0.15, which is somewhat lower than the Butcher-Oemler average at z similar to 0.5. The value of f(B) is found to increase with limiting magnitude and with radius from the centre.