Number Density Evolution of Ks -band Selected High Redshift Galaxy Populations in the AKARI North Ecliptic Pole Field

TL;DR

This study analyzes the number density evolution of high-redshift galaxy populations selected in the Ks-band in the AKARI NEP field, comparing observations with evolutionary models to understand galaxy formation and evolution.

Contribution

It provides new observational counts of high-redshift galaxy populations and tests evolutionary models, highlighting the need for density evolution in passive galaxy counts.

Findings

Pure luminosity evolution models without density evolution fail at faint magnitudes.

Negative density evolution models fit the observed passive galaxy counts.

Dusty ERO counts can be explained by submillimetre galaxy contributions.

Abstract

We present the number counts of Ks-band selected high redshift galaxy populations such as extremely red objects (EROs), B, z & K -band selected galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The final catalogue contains 308 EROs (Ks<19.0 ; 54 percent 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 near-infrared EROs can be explained by the source densities of the far-infrared - submillimetre populations. Our model predicts that the dusty ERO source counts can be explained assuming a 25 percent contribution of submillimetre star-forming galaxies with the majority of brighter Ks -band detected dusty EROs having luminous (rather than HR10 type ultra-luminous) submillimetre counterparts. We propose that the fainter Ks>19.5 population is dominated by the sub-millijansky submillimetre population. We also predict a turnover in in dusty ERO counts around 19<Ks<20.