EDP Sciences
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Volume 368, Number 3, March IV 2001
Page(s) 787 - 796
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010057

A&A 368, 787-796 (2001)
DOI: 10.1051/0004-6361:20010057

The Calar Alto Deep Imaging Survey: K-band Galaxy number counts

J.-S. Huang1, 2, D. Thompson3, 2, M. W. Kümmel2, K. Meisenheimer2, C. Wolf2, S. V. W. Beckwith4, 2, R. Fockenbrock2, J. W. Fried2, H. Hippelein2, B. von Kuhlmann2, S. Phleps2, H.-J. Röser2 and E. Thommes2

1  Present address: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
2  Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
3  Present address: California Institute of Technology, MS 320-47, Pasadena, CA 91125, USA
4  Present address: STScI, 3700 San Martin Dr., Baltimore, MD 21218, USA

(Received 17 April 2000 / Accepted 4 January 2001)

We present K-band number counts for the faint galaxies in the Calar Alto Deep Imaging Survey (CADIS). We covered 4 CADIS fields, a total area of $0.2 \rm {deg}^2$, in the broad band filters B, R and K. We detect about 4000 galaxies in the K-band images, with a completeness limit of $K=19.75 \rm {mag}$, and derive the K-band galaxy number counts in the range of $14.25 < K <
19.75 \rm {mag}$. This is the largest medium deep K-band survey to date in this magnitude range. The B- and R-band number counts are also derived, down to completeness limits of $B=24.75 \rm {mag}$ and $R=23.25 \rm {mag}$. The K-selected galaxies in this magnitude range are of particular interest, since some medium deep near-infrared surveys have identified breaks of both the slope of the K-band number counts and the mean B-K color at $K=17\sim18 \rm {mag}$. There is, however, a significant disagreement in the K-band number counts among the existing surveys. Our large near-infrared selected galaxy sample allows us to establish the presence of a clear break in the slope at $K=17.0 \rm {mag}$ from dlog N/dm = 0.64 at brighter magnitudes to dlog N/dm = 0.36 at the fainter end. We construct no-evolution and passive evolution models, and find that the passive evolution model can simultaneously fit the B-, R- and K-band number counts well. The B-K colors show a clear trend to bluer colors for $K > 18 \rm {mag}$. We also find that most of the K=18- $20 \rm {mag}$ galaxies have a B-K color bluer than the prediction of a no-evolution model for an L* Sbc galaxy, implying either significant evolution, even for massive galaxies, or the existence of an extra population of small galaxies.

Key words: cosmology: observations -- galaxies: evolution -- galaxy: formation -- surveys -- infrared: galaxies

Offprint request: J.-S. Huang, jhuang@cfa.harvard.edu

© ESO 2001

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