GaBoDS: The Garching‐Bonn Deep Survey

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).

The structure and evolution of a forming galaxy cluster atz= 1.62

“…The Balmer break is tightly bracketed by the FORS [SIII]+65 and Y filters, whilst the 4000Å break is sampled by the Y , NB1.06 and J filters (see Fig 1). The images were reduced using the publicly available THELI software (Erben et al 2005;Schirmer 2013). Flux calibration was achieved by linearly interpolating the photometry of the H13 catalogue, and this catalogue was again used as the basis for the astrometric calibration.…”

HALOGAS: Extraplanar gas in NGC 3198

“…NGC 3198 was observed in the r -band on February 4, 2010, and the total on-source time amount was 3600 s. A co-added image was obtained using the THELI 1 imaging reduction pipeline (Schirmer et al 2003;Erben et al 2005). After the overscan-and bias correction, the images were flat-fielded, super-flat-fielded and defringed.…”

A normal abundance of faint satellites in the fossil group NGC 6482

“…The knowledge of the absolute gain value for the B-band data is not necessary because absolute Schlegel et al (1998) photometric calibration was achieved with the standard star exposures, themselves corrected with the same relative gain as the science data. The THELI image reduction pipeline (Erben et al 2005) then was used for the remaining steps of data preprocessing. The astrometric calibration from the THELI reductions was based on cross-correlation with the PPMXL catalog of point sources using the scamp software.…”