Subaru Observations for the K-Band Luminosity Distribution of Galaxies in Clusters near to 3C 324 at z ∼ 1.2

We investigate the K-band luminosity distribution of galaxies in the region of clusters at z ∼ 1.2 near to the radio galaxy 3C 324. The imaging data were obtained during the commissioning period of the Subaru telescope. There is a significant excess of the surface number density of the galaxies with K = 17–20 mag in the region within ∼ 40″ from 3C 324. At this bright end, the measured luminosity distribution shows a drop, which can be represented by the exponential cut off of the Schechter-function formula; the best-fitted value of the characteristic magnitude, K^*, is ∼ 18.4±0.8. This measurement follows the evolutionary trend of the K^* of the rich clusters observed at an intermediate redshift, which is consistent with passive evolution models with a formation redshift zf ≳ 2. At K ≳ 20 mag, however, the excess of the galaxy surface density in the region of the clusters decreases abruptly, which may imply that the luminosity function of the cluster galaxies has a negative slope at the faint end. This may imply strong luminosity segregation between the inner and outer parts of the clusters, or some deficit of faint galaxies in the cluster central region of the cluster.