We present a weak shear analysis of the Abell 901/902 supercluster, composed of three rich clusters at z = 0.16. Using a deep R-band image from the 0.5 • × 0.5 • MPG/ESO Wide Field Imager together with supplementary Bband observations, we build up a comprehensive picture of the light and mass distributions in this region. We find that, on average, the light from the early-type galaxies traces the dark matter fairly well, although one cluster is a notable exception to this rule. The clusters themselves exhibit a range of mass-to-light (M/L) ratios, X-ray properties, and galaxy populations. We attempt to model the relation between the total mass and the light from the early-type galaxies with a simple scale-independent linear biasing model. We find M/L B = 130h for the early type galaxies with zero stochasticity, which, if taken at face value, would imply Ω m < 0.1. However, this linear relation breaks down on small scales and on scales equivalent to the average cluster separation (∼1 Mpc), demonstrating that a single M/L ratio is not adequate to fully describe the mass-light relation in the supercluster. Rather, the scatter in M/L ratios observed for the clusters supports a model incorporating non-linear biasing or stochastic processes. Finally, there is a clear detection of filamentary structure connecting two of the clusters, seen in both the galaxy and dark matter distributions, and we discuss the effects of cluster-cluster and cluster-filament interactions as a means to reconcile the disparate descriptions of the supercluster.

We present initial results from a Ðeld survey for extremely red objects [EROs, deÐned here as (R[K@) º 6 mag] covering 154 arcmin2 of sky, from the Ðrst of seven deep, wide-Ðeld K@ images obtained as part of the Calar Alto Deep Imaging Survey (CADIS). The 5 p point source detection limits are K@ \ 20.5 mag and R \ 25.0 mag, while extended-source limits are up to 0.50È0.75 mag brighter. We identify a total of eight bright EROs with K@ ¹ 19.0 mag. Six of these bright EROs are resolved and are likely to be galaxies, while the remaining two are unresolved, with colors consistent with their being low-mass galactic stars. We derive a surface density for the six bright, extragalactic EROs of 0.039^0.016 arcmin~2, which is higher by a factor of 4 than previous values. We estimate that the volume density of bright EROs to be as high as that of nearby Seyfert galaxies.

Context. Many current and future surveys aim to detect the highest redshift (z > ∼ 7) sources through their Lyman-α (Lyα) emission, using the narrow-band imaging method. However, to date the surveys have only yielded non-detections and upper limits as no survey has reached the necessary combination of depth and area to detect these very young star forming galaxies. Aims. We aim to calculate model luminosity functions and mock surveys of Lyα emitters at z > ∼ 7 based on a variety of approaches calibrated and tested on observational data at lower redshifts. Methods. We calculate model luminosity functions at different redshifts based on three different approaches: a semi-analytical model based on CDM, a simple phenomenological model, and an extrapolation of observed Schechter functions at lower redshifts. The results of the first two models are compared with observations made at redshifts z ∼ 5.7 and z ∼ 6.5, and they are then extrapolated to higher redshift.Results. We present model luminosity functions for redshifts between z = 7−12.5 and give specific number predictions for future planned or possible narrow-band surveys for Lyα emitters. We also investigate what constraints future observations will be able to place on the Lyα luminosity function at very high redshift. Conclusions. It should be possible to observe z = 7−10 Lyα emitters with present or near-future instruments if enough observing time is allocated. In particular, large area surveys such as ELVIS (Emission Line galaxies with VISTA Survey) will be useful in collecting a large sample. However, to get a large enough sample to constrain well the z ≥ 10 Lyα luminosity function, instruments further in the future, such as an ELT, will be necessary.

Abstract. We use a multi-color classification method introduced by Wolf et al. (2001) to reliably identify stars, galaxies and quasars in the up to 16-dimensional color space provided by the filter set of the Calar Alto Deep Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained this way have been used for dedicated studies which are published in separate papers. The classification is good enough to detect quasars rather completely and efficiently without confirmative spectroscopy. The multi-color redshifts are accurate enough for most statistical applications, e.g. evolutionary studies of the galaxy luminosity function. Also, the separation between stars and galaxies reaches deeper than with morphological criteria, so that studies of the stellar population can be extended to fainter levels. We characterize the dataset presently available on the CADIS 1 h-, 9 h-and 16 h-fields. Using Monte-Carlo simulations we model the classification performance expected for CADIS. We present a summary of the classification results on the CADIS database and discuss unclassified objects. More than 99% of the whole catalog sample at R < 22 (more than 95% at R < 23) are successfully classified matching the expectations derived from the simulations. A small number of peculiar objects challenging the classification is discussed in detail. Spectroscopic observations are used to check the reliability of the multi-color classification (6 mistakes among 151 objects with R < 24). From these, we also determine the accuracy of the multi-color redshifts which are rather good for galaxies (σz ≈ 0.03) and useful for quasars. We find that the classification performance derived from the simulations compares well with results from the real survey. Finally, we locate areas for potential improvement of the classification.

Abstract. 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 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 mag, and derive the K-band galaxy number counts in the range of 14.25 < K < 19.75 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 mag and R = 23.25 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 ∼ 18 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 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 mag. We also find that most of the K = 18-20 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.