A&A 370, 384-397 (2001)
DOI: 10.1051/0004-6361:20010218

A wide field survey at the Northern Ecliptic Pole

II. Number counts and galaxy colours in B_j, R, and K

M. W. Kümmel^{1, 2} and S. J. Wagner<sup>2

1</sup>  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²  Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, 69117 Heidelberg, Germany

(Received 22 May 2000 / Accepted 2 February 2001)

Abstract
We present a medium deep survey carried out in the three filters B_j, 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 17.5 mag in B_j, 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 B_jRK-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 B_j 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 B_j-R and R-K down to B_j=24.0 and K=18.0 mag, 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 R-K despite flawless fits to the colour distributions in the optical (B_j-R). The B_jRK data collected over a large area provides the opportunity to select rare objects like candidates for high-redshift galaxies and extremely red objects (EROs, R-K> 5.0) 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 K< 16.5 mag, 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

Offprint request: M. W. Kümmel, kuemmel@mpia-hd.mpg.de

SIMBAD Objects

© ESO 2001

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.