No abstract

Aims. An interesting question of contemporary cosmology concerns the relation between the spatial distribution of galaxies and dark matter, which is thought to be the driving force behind the structure formation in the Universe. In this paper, we measure this relation, parameterised by the linear stochastic bias parameters, for a range of spatial scales using the data of the Garching-Bonn Deep Survey (GaBoDS). Methods. The weak gravitational lensing effect is used to infer matter density fluctuations within the field-of-view of the survey fields. This information is employed for a statistical comparison of the galaxy distribution to the total matter distribution. The result of this comparison is expressed by means of the linear bias factor b, the ratio of density fluctuations, and the correlation factor r between density fluctuations. The total galaxy sample is divided into three sub-samples using R-band magnitudes and the weak lensing analysis is applied separately for each sub-sample. Together with the photometric redshifts from the related COMBO-17 survey we estimate the typical mean redshifts of these samples withz = 0.35, 0.47, 0.61, respectively. Results. Using a flat ΛCDM model with Ω m = 0.3, Ω Λ = 0.7 as fiducial cosmology, we obtain values for the galaxy bias on scales between 1 ≤ θ ap ≤ 20 . At 10 , the median redshifts of the samples correspond roughly to a typical comoving scale of 3, 5, 7 h −1 Mpc with h = 0.7, respectively. We find evidence for a scale-dependence of b. Averaging the measurements of the bias over the range 2 ≤ θ ap ≤ 19 yieldsb = 0.81 ± 0.11, 0.79 ± 0.11, 0.81 ± 0.11 (1σ), respectively. Galaxies are thus less clustered than the total matter on that particular range of scales (anti-biased). As for the correlation factor r we see no scale-dependence within the statistical uncertainties; the average over the same range isr = 0.61 ± 0.16, 0.64 ± 0.18, 0.58 ± 0.19 (1σ), respectively. This implies a possible decorrelation between galaxy and dark matter distribution. An evolution of galaxy bias with redshift is not found, the upper limits are: ∆b 0.2 and ∆r 0.4(1σ).

Aims. In this paper the optical data of the ESO Deep-Public-Survey observed with the Wide Field Imager and reduced with the THELI pipeline are described. Methods. Here we present 63 fully reduced and stacked images. The astrometric and photometric calibrations are discussed and the properties of the images are compared to images released by the ESO Imaging Survey team covering a subset of our data. Results. These images are publicly released to the community. Our main scientific goals with this survey are to study the high-redshift universe by optically pre-selecting high-redshift objects from imaging data and to use VLT instruments for follow-up spectroscopy as well as weak lensing applications.

We present results of a search for bright Lyman break galaxies at 1.5 ≤ z ≤ 2.5 in the GOODS-S field using a NUV-dropout technique in combination with color-selection. We derived a sample of 73 LBG candidates. We compare our selection efficiencies to BM/BX-and BzK methods (techniques solely based on ground-based data sets), and find the NUV data to provide greater efficiency for selecting star-forming galaxies. We estimate LBG candidate ages, masses, star formation rates, and extinction from fitting PEGASE synthesis evolution models. We find about 20% of our LBG candidates are comparable to infrared luminous LBGs or sub-millimeter galaxies which are thought to be precursors of massive elliptical galaxies today. Overall, we can show that although BM/BX and BzK methods do identify star-forming galaxies at z ∼ 2, the sample they provide biases against those star-forming galaxies which are more massive and contain sizeable red stellar populations. A true Lyman break criterion at z ∼ 2 is therefore more directly comparable to the populations found at z ∼ 3, which does contain a red fraction.