Number density evolution of Ks-band-selected high-redshift galaxy Populations in the AKARI north ecliptic pole field

We present the number counts of Ks-band-selected high- redshift galaxy populations such as extremely red objects (EROs), B-, z-, and K- bandYselected galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. These high- redshift galaxy samples are extracted from a multicolor catalog combining optical data from SuprimeCam on the 8.2 m Subaru Telescope with near- infrared data from the Florida Multiobject Imaging Near- IR Grism Observational Spectrometer on the Kitt Peak National Observatory 2.1 m telescope over 540 arcmin2 in the NEP region field. The final catalog contains 308 EROs (Ks < 19: 0; 54% are dusty star- forming EROs, and the rest are passive old EROs), 137 star- forming BzKs, and 38 passive old BzKs (Ks < 19: 0) and 64 DRGs (Ks < 18: 6). We also produce individual component source counts for both the dusty star- forming and passive populations. We compare the observed number counts of the high redshift passively evolving galaxy population with a backward pure luminosity evolution (PLE) model allowing different degrees of number density evolution. We find that the PLE model without density evolution fails to explain the observed counts at faint magnitudes, while the model incorporating negative density evolution is consistent with the observed counts of the passively evolving population. We also compare our observed counts of dusty star- forming EROs with a phenomenological evolutionary model postulating that the nearinfrared EROs can be explained by the source densities of the far- infraredYsubmillimeter populations. Our model predicts that the dusty ERO source counts can be explained assuming a 25% contribution of submillimeter starforming galaxies with the majority of brighter Ks- bandYdetected dusty EROs having luminous (rather than HR 10 type ultraluminous) submillimeter counterparts. We propose that the fainter Ks > 19: 5 population is dominated by the submillijansky submillimeter population. We also predict a turnover in dusty ERO counts around 19 < Ks < 20.