The ESO K'-band Galaxy Survey - Galaxy Counts

We present K'-band galaxy counts in the magnitude range $13 < K' < 20$, obtained from two independent surveys near the South Galactic Pole, covering an area of $\sim 40 arcmin^2$ and $\sim 170 arcmin^2$, including $\sim 200$ and $\sim 1000$ objects respectively up to a magnitude limit $K' \sim 20.0$ and $K'\sim 19.0$. At magnitudes $K > 18.5$ we surveyed an area more than 7 times wider that covered by previous K-band surveys. Our counts are quite in good agreement with those in the literature at magnitudes brighter than $K \sim 17$, while are systematically lower at fainter magnitudes. We confirm a change in the slope of the $dlogN/dm$ relation at $K' \sim 17$ from 0.57 to 0.35, but do not find the bump shown by other K-band surveys in the magnitude range $16 < K < 20$. Furthermore 10% of the galaxies brighter than $K' \sim 18$ have $B-K'<3$. We suggest that these blue objects represent a population of sub-$L^*$ nearby evolving galaxies.