II. Number counts and galaxy colours in Bj, R, and K
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
2 Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, 69117 Heidelberg, Germany
Corresponding author: M. W. Kümmel, email@example.com
Accepted: 2 February 2001
We present a medium deep survey carried out in the three filters Bj, R and K. The survey covers homogeneously the central square degree around the Northern Ecliptic Pole (NEP) down to a completeness limit (95% ) of 24.25, 23.0 and in Bj, R and K, respectively. While the near infrared data have been presented in the first paper of this series, here we concentrate on the optical data and the results based on the combined BjRK-data. The unique combination of area and depth in our survey allows to perform a variety of investigations based on homogeneous material covering more than ten magnitudes in apparent brightness. We analyze the number counts for point-like and extended sources in Bj and R to determine the slopes in and to test for possible breaks therein. While we can confirm the slopes found in previous works with a higher statistical significance, the largest uncertainty remaining for the amplitudes is galactic extinction. We determine the colour distributions of galaxies in Bj-R and down to Bj=24.0 and , respectively. The distributions in both colours are modeled using galaxy spectral evolution synthesis. We demonstrate that the standard models of galaxy evolution are unable to reproduce the steady reddening trend in despite flawless fits to the colour distributions in the optical (Bj-R). The BjRK data collected over a large area provides the opportunity to select rare objects like candidates for high-redshift galaxies and extremely red objects (EROs, ) and to determine their surface density. Our EROs are selected at an intermediate magnitude range and contain contribution from both galactic as well as extragalactic sources. At , where a morphological classification is possible, the stellar component dominates the sample.
Key words: surveys / stars: statistics / galaxies: evolution / galaxies: photometry / galaxies: statistics / infrared: galaxies
Based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, operated by the Max-Planck-Institut für Astronomie, Heidelberg, jointly with the Spanish National Commission for Astronomy.
© ESO, 2001